Cover Image
close this bookHIV and Infant Feeding - Review of HIV Transmission Through Breastfeeding Jointly Issued by UNICEF, UNAIDS and WHO Guidelines - Prevention of Mother-to-Child Transmission (UNAIDS, 1998, 26 p.)
View the document(introduction...)
View the documentExplanation of terms
View the documentIntroduction
Open this folder and view contentsMother-to-child transmission
Open this folder and view contentsEvidence for breast-milk transmission
View the documentFactors associated with the risk of mother-to-child transmission
Open this folder and view contentsAnti-infective properties of breast milk in women with HIV
Open this folder and view contentsStrategies to reduce breast-milk transmission
View the documentSummary and Conclusion
View the documentReferences

(introduction...)

UNAIDS
UNICEF · UNDP · UNFPA
UNESCO · WHO · WORLD BANK


WHO/FRH/NUT/CHD 98.3
UNAIDS 98.5
UNICEF/PD/NUT(J) 98-3
Distr.: General
Original: English

Reprinted with revisions, December 1998
© World Health Organization 1998
® Joint United Nations Programme on HIV/AIDS (UNAIDS) 1998

This document is not a formal publication of the World Health Organization (WHO) and UNAIDS, but all rights are reserved by these agencies. The document may, however, be freely reviewed, abstracted, reproduced and transmitted, in part or in whole, but not for sale nor for use in conjunction with commercial purposes.

For authorization to translate the work in full, and for any use by commercial entities, application and enquiries should be addressed to the Programme of Nutrition, World Health Organization, Geneva, Switzerland, which will be glad to provide the latest information on any changes made to the text, plans for new editions, and the reprints and translations that are already available.

The designations employed and the presentation of the material in this work do not imply the expression of any opinion whatsoever on the part of WHO and UNAIDS concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers and boundaries.

The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by WHO and UNAIDS in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters.

Explanation of terms

AZT (also known as Zidovudine (ZDV)) is an antiretroviral drug which inhibits HIV replication. It is used in the prevention of mother-to-child transmission.

Breast-milk substitute means any food being marketed or otherwise represented as a partial or total replacement for breast milk, whether or not suitable for that purpose.

CD4 cells means main target cells for HIV. CD4 lymphocytes (a type of white blood cells) are key in both humoral and cell-mediated immune responses. Their number decreases during HIV infection.

CD8 cells means lymphocytes which play an important role in fighting infections. Their number may be increased during HIV infection.

Cell-associated virus means HIV which lives inside the cell, measured as HIV-DNA.

Cell-free virus means parts of the virus (virions) not associated with a cell, measured as HIV-RNA.

Cervical ectopy means a turning outward of the edges of the endocervix; it may result from chronic inflammation of the cervix.

Cessation of breastfeeding means stopping breastfeeding.

Chorioamnionitis means inflammation of the fetal membranes, associated with a bacterial or parasitic infection (e.g. malaria).

Colostrum is the thick yellow milk secreted by the breasts during the first few days after delivery, that gradually evolves into mature milk at 3-14 days postpartum. It contains more antibodies and white blood cells than mature breast milk.

Commercial infant formula means a breast-milk substitute formulated industrially in accordance with applicable Codex Alimentarius standards to satisfy the nutritional requirements of infants up to four to six months of age.

Complementary food means any food, whether manufactured or locally prepared, suitable as a complement to breast milk or to infant formula, when either becomes insufficient to satisfy the nutritional requirements of the infant.

DNA, an abbreviation for deoxyribonucleic acid, is the carrier of genetic information found in cell nuclei.

Early breastfeeding means breastfeeding in the first 3 weeks of life.

Early postpartum means the first 3-6 weeks after delivery.

Enterocyte is the cell of the lining of the intestinal wall.

Epithelial means the surface layer of cells covering cutaneous, mucosal and serous surfaces.

Exclusive breastfeeding means giving an infant no other food or drink, not even water, apart from breast milk (including expressed breast milk), with the exception of drops or syrups consisting of vitamins, mineral supplements or medicines.

Glycosaminoglycans means linear polysaccharides composed of repeating disaccharides, usually more than 20 per chain, that attach to a protein core forming a proteoglycan. They are macromolecules that may inhibit the binding of HIV to the CD4 receptor.

Human immunodeficiency virus (HIV) refers to HIV-1 in this document, since cases of mother-to-child transmission of HIV-2 are rare.

Immunoglobulins means any of the five distinct antibodies present in the serum and external secretions of the body (IgA, IgD, IgE, IgG and IgM).

Infant means a child from birth to 12 months of age.

Intestinal lumen means the space within the tubular part of the bowel.

Intrapartum means the period during labour or delivery.

Lactoferrin means an iron-binding protein found in human milk.

Late postnatal transmission means a breastfed child who becomes infected with HIV only after 3-6 months of age. Definitions of late postnatal transmission vary between studies.

Lipase means any fat-splitting enzyme.

Lipid means any one of a widely varying group of fats and fat-like organic substances.

Macrophage means a large "wandering" phagocytic cell that ingests foreign matter, and plays an important role in resisting infection.

Mature breast milk means milk produced from about 14 days postpartum to the cessation of breastfeeding.

Meta-analysis means the statistical method of combining the results of similar, but separate, studies.

M-cells means specialised epithelial cells found on the intestinal mucosa.

Mixed feeding means partial breastfeeding and giving some other milk, often bottles of infant formula.

Mother-to-child transmission (MTCT) means transmission of HIV to a child from an HIV-infected woman during pregnancy, delivery or breastfeeding. The term "vertical transmission" is commonly used interchangeably with MTCT.

Mucosa means mucous membranes.

Neonatal describes the period immediately following birth and continuing through the first month of life.

P24 antigen means a protein part of the virus membrane that can stimulate the production of specific antibodies

PCR means polymerase chain reaction, a laboratory method in which the genetic material (DNA or RNA) of the virus is detected and amplified. It can be both qualitative or quantitative.

Partial breastfeeding means some breastfeeding while giving other forms of food.

Replacement feeding means the process of feeding a child, who is not receiving any breast milk, with a diet that provides all the nutrients the child needs. During the first six months this should be with a suitable breast-milk substitute – commercial infant formula, or home-prepared formula with micronutrient supplements. After six months this should preferably be with a suitable breast-milk substitute, and complementary foods made from appropriately prepared and nutrient-enriched family foods that are given three times a day. If breast-milk substitutes are not available, appropriately prepared family foods should be further enriched and given five times a day.

RNA means ribonucleic acid, a substance found in the nucleus of all living cells and in many viruses. It is an intermediate of DNA and the medium by which genetic instructions from the nucleus are transmitted to the rest of the cell.

Supernatant means the upper layer of material, liquid or lighter solid, that remains after the precipitation of a solid part of a mixture.

Synctium-forming virus means a virus that has the ability to form a network, thus involving cells that are not strictly infected.

Tropism means a predilection for a specific tissue.

Viral culture means growth of virus on artificial media under ideal conditions for growth.

Wet-nursing means the breastfeeding of an infant by someone other than the infant's mother.

Introduction

In the past three decades, strategies to reduce child mortality and to promote family health have resulted in considerable improvements in child health (World Development Report, 1993). Promotion of breastfeeding has played an important role since breastfeeding contributes to reduced mortality by providing optimum nutrition, by protecting against common childhood infections, and by its child-spacing effects (American Academy of Pediatrics, 1997; Golding et al., 1997; Goldman, 1993; De Soyza et al., 1991; Akr1990; Monteiro et al., 1990; Thapa et al., 1989; Habicht et al.,1988; Victora et al., 1987).

However, the emergence of HIV threatens to reverse gains in child health, since children are at risk of acquiring HIV infection through transmission from an HIV-infected mother. It is recognized that breastfeeding by an HIV-infected mother increases the risk of HIV transmission to her infant.

Since the beginning of the HIV pandemic, approximately three million children under 15 years of age worldwide have been infected with HIV and current estimates suggest that 600 000 children are newly infected annually (UNAIDS/WHO, 1998). The majority of these children live in sub-Saharan Africa, where between 25-40% of HIV-infected children die before their fifth birthday, and HIV is already contributing to increased childhood mortality (UNAIDS/WHO, 1998; Ryder et al., 1994; Nesheim et al., 1994). Although HIV transmission through breastfeeding is only partially responsible for this increase, HIV and infant feeding is an important public health issue, particularly in regions where HIV prevalence is high, and infectious diseases and malnutrition are the leading causes of childhood death. Countries need to develop sound policies regarding the prevention of HIV transmission through breastfeeding while continuing to protect, promote and support breastfeeding for infants of HIV-negative women and women of unknown serostatus.

This document reviews current scientific knowledge about breast-milk transmission of HIV, and serves as the foundation for two complementary documents:

HIV and infant feeding: Guidelines for decision-makers1
HIV and infant feeding: A guide for health care managers and supervisors2

1 Guidelines for decision-makers, 1998, 36 pages [E]; WHO/FRH/NUT/CHD 98.1
2 A Guide for Health Care Managers and Supervisors, 1998, 36 pages [E]; WHO/FRH/NUT/CHD 98.2

(introduction...)

Mother-to-child transmission (MTCT) of HIV, which can occur during pregnancy, delivery or breastfeeding, is responsible for more than 90% of HIV infection in children worldwide (UNAIDS/WHO, 1998). The present review focuses on HIV-1. Both HIV type 1 (HIV-1) and HIV type 2 (HIV-2) can be transmitted from mother to child, but HIV-2 is transmitted much less frequently, as it is less pathogenic than HIV-1 (Adjorlolo-Johnson et al., 1994; Andreasson et al., 1993; Morgan et al., 1990).

The remaining 10% of paediatric infections are attributed to transfusion with contaminated blood and blood products, use of contaminated medical equipment, other practices that cut or pierce the skin, or sexual contact (MAP, 1998; UNAIDS/WHO, 1998; Tovo et al., 1988).

HIV infection in women

Most children acquire the virus through transmission from an HIV-infected mother, therefore, the incidence of paediatric HIV reflects that of HIV infection in women of childbearing age. In areas of high seroprevalence, a significant number of children are at risk.

Mother-to-child transmission (MTCT) of HIV focuses attention on women, but the use of the term MTCT is not to imply blame, whether or not a woman is aware of her own infection status. A woman can acquire HIV through unprotected sex with an infected partner, by receiving contaminated blood, or through exposure to unsterile instruments or medical procedures. HIV is often introduced into the family through the woman's sexual partner, often the father of her child.

The prevalence of HIV varies considerably from region to region. Women and children in sub-Saharan Africa are disproportionately affected, with eight in every 10 HIV-infected women worldwide, and nine in every 10 newly infected children living in this region (MAP, 1998; UNAIDS/WHO, 1998). In West and Central Africa, HIV prevalence in pregnant women currently reaches 10-15% in some urban areas and 1-5% in others. Prevalences in East Africa are higher at 15-25% in urban areas and 5-10% in rural areas, while in Southern Africa antenatal seroprevalences of 20-30%, and in some places even as high as 40%, have been reported (MAP, 1998; UNAIDS/WHO, 1998). In the Caribbean, Central America and South America, HIV-1 seroprevalence rates currently range from 0.1% - 5.0%. Asia is experiencing a rapidly growing epidemic with seroprevalence rates in big cities of Cambodia, India and Thailand currently ranging from 1-5% (UNAIDS/WHO, 1998).

Rates of mother-to-child transmission

Estimates of the rate of mother-to-child transmission of HIV in cohorts of women who have not received any preventive treatment (such as antiretrovirals) range from 15-25% in industrialized countries to 25-45% in developing countries (Msellati et al., 1995). The highest rates of MTCT have been found in women in Africa (Kind et al., 1998; Maguire et al., 1997; Ometto et al., 1995; Lallemant, Le Coeur et al., 1994; Roques et al., 1993; European Collaborative Study, 1992; Blanche et al., 1989).

Differences in study methods, the composition of the populations studied, and the prevalence of co-factors of transmission may explain some of these differences. However, it is likely that much of the increased rate of transmission seen in women in sub-Saharan Africa is associated with breastfeeding,1 where many women breastfeed for about 2 years (The Working Group on Mother-to-Child Transmission, 1995; Ryder and Behets, 1994; Dabis et al., 1993).

1 Many women who breastfeed do not breastfeed exclusively. Other fluids (juices, milks, teas) and foods may also be given to the infant. In many studies looking at HIV transmission and breastfeeding no differentiation is made between women who "exclusively" or "partially" breastfeed. In this document, unless otherwise stated, "breastfeeding women" will often include both women who "exclusively" or "partially" breastfeed.

In an attempt to quantify the relative contribution of intrauterine and intrapartum transmission of HIV in non-breastfed infants, a working definition of timing has been proposed (Bryson et al., 1992).

In utero infection. In this, a child is classified as having been infected during pregnancy (in utero) if HIV-1 genome is detected within 48 hours of delivery by polymerase chain-reaction test (DNA-PCR) or viral culture.

Intrapartum infection. Acquisition of infection is assumed to have occurred during delivery (intrapartum) if these diagnostic tests were negative in a sample taken during the first 48 hours after delivery, but became positive in subsequent samples taken within 7-90 days of delivery.

Following this classification, a French study estimated that of the infants infected with HIV, 35% of the non-breastfed infants studied were infected before birth and 65% were infected late in pregnancy or during delivery (Rouzioux et al., 1995). A recent review indicated that in women who did not breastfeed their infants, about one-third of MTCT infection was acquired during the intrauterine period. In women who did breastfeed their infants, less than a quarter of all MTCT was acquired during the intrauterine period (Newell, 1998).

Table 1. Percentage HIV infection acquired by different routes *


Partially breastfed/breastfed infants

Non-breastfed infants

During intrauterine period

20%

33%

During delivery

45-50%

67%

Postpartum, by breastfeeding

30-35%

0

*These rates are observed in the absence of interventions to reduce MTCT

(introduction...)

Breast-milk transmission of HIV has been well documented. The first reports indicating the possibility of HIV-1 transmission through breast milk were in breastfed infants of women who were infected postnatally through blood transfusion or through heterosexual exposure (Palasanthiran et al., 1993; Van de Perre et al., 1991; Stiehm and Vink, 1991; Hira et al., 1990; Colebunders et al., 1988; Lepage et al., 1987; Ziegler et al., 1985;). There were also reports of infants, with no other known exposure to HIV, who were infected through wet-nursing and through pooled breast milk (Nduati et al., 1994; Colebunders et al., 1988;).

Generally, higher rates of mother-to-child transmission of HIV are observed where most infants are breastfed rather than where fewer infants are breastfed. However, other reasons for variations in transmission rates, such as maternal nutritional status, stage of HIV disease and possible differences in transmission of HIV subtypes cannot be excluded. Additional evidence is provided by results from prospective studies which indicate that among infants born to HIV-infected mothers, those who are breastfed are more likely to be infected than those who are formula-fed, even allowing for other factors known to be associated with mother-to-child transmission of HIV (European Collaborative Study, 1992; Ryder, 1991; Blanche et al., 1989; Tovo et al., 1988; Tess et al., 1998a).

Mechanisms of breast-milk transmission

Although HIV has been detected in breast milk, (Nduati, 1995; Ruff, 1994; Van de Perre et al., 1993) mechanisms of breast-milk transmission are not yet fully understood. The respective roles of cell-free and cell-associated virus in breast-milk transmission are not known, nor is the association between plasma and milk virus levels understood. The portal of entry for the virus via the infant mucosa also merits further investigation.

Animal models have been used to explore potential mechanisms of transmission. It is possible to infect neonatal rhesus monkeys with simian immunodeficiency virus (Baba et al., 1994) and kittens with feline immunodeficiency virus (Sellon et al., 1994) by applying cell-free virus on the mucosa. This suggests that cell-free HIV in breast milk could infect cells of the intestinal mucosa. M-cells, which are specialized epithelial cells found in the Peyer's patches of the intestinal mucosa, may be a mechanism allowing infectious agents such as HIV to cross the intact mucosa. M-cells engulf and transport the pathogen and present it to macrophages that indent the serosal surface of the M-cell (Featherstone, 1997). Results from in vitro studies on rabbit M cells suggest that HIV-1 particles could use M cells to cross the intestinal barrier (Amerongen et al., 1991). A recent in vitro study indicated that HIV-infected cells themselves may also play an important role by stimulating ordinary enterocytes to engulf HIV particles presented by HIV-infected cells in the intestinal lumen (Bomsel, 1997). Moreover, HIV RNA has been detected in the oropharyngeal and gastric aspirates of a substantial proportion of infants born to HIV-infected mothers (Nielsen et al., 1996, Ait-Khaled et al., 1998).

Quantifying the risk of breast-milk transmission

Early studies investigating the frequency of breast-milk transmission and associated factors were limited by small numbers as well as by the predominance of one method of infant feeding in any one cohort (European Collaborative Study, 1992; Ryder, 1991; Blanche et al., 1989; Tovo et al., 1988).

In 1992, a meta-analysis was carried out using data from four studies reporting on 42 recently infected women and six studies reporting on 1772 women with established infection. The majority of the women had breastfed for 2-4 weeks, and 106 women had breastfed for longer than six months. The estimated additional risk of transmission from breast milk, above that occurring during pregnancy and delivery, among women with established HIV infection, was approximately 15% (95% Confidence Interval 7-22%) (Dunn et al., 1992). However, 15% may be an under-estimation among women who breastfeed for longer periods of time.

The risk of transmission through breast milk among women with recent infection (HIV infection acquired in the postpartum period) was nearly twice as high (29% (95% CI 16-42%)).

Insufficient information is available to estimate the exact association between duration of breastfeeding and the risk of transmission. However, there is strong evidence for a gradual and continued increase in transmission risk as long as the child is breastfed (Taha et al., 1998, Leroy et al., 1998).

Timing of HIV transmission during breastfeeding

Transmission of HIV through breast milk can take place at any point during lactation. The persistence of maternal antibodies and the presence of a "window period" during which infection is undetectable using currently available technology, make it impossible to determine whether an infant has been infected during delivery (intrapartum) or through breastfeeding in the period following birth. Therefore, when seropositive women breastfeed their infants, it is not possible to differentiate between HIV transmission attributable to delivery and that resulting from breastfeeding from birth. (Newell, 1998; Bobat et al., 1997; Mandelbrot et al., 1996; Bertolli et al., 1996; Simonon et al., 1994; Datta et al., 1994).

Later postnatal transmission through breastfeeding can be determined using currently available diagnostic tools. Studies of infants found to be negative by PCR testing at 2-6 months of age, but who subsequently showed evidence of infection, have provided estimates of the risk of late postnatal transmission (after 3-6 months of age) ranging from 4-12% (Ekpini et al., 1997; Karlsson et al., 1997; Bertolli et al., 1996; Simonon et al., 1994).

Table 2. Studies of the risk of late postnatal transmissions

Study

Time of negative PCR

Median length of breastfeeding

Risk of HIV infection through late postnatal breastfeeding

Number of infants in study

Leroy et al., 1998(meta-analysis)

2.5-15.7 months

15 months

9.2%

429

Taha et al., 1998

7 weeks

Not available

9.6%

621






Ekipini et al., 1997

3-6 months

20 months

12%

45






Bertolli et al., 1996

3-5 months

12 months

4%

189






Simonon et al., 1994

3 months

19 months

4.9%

180

Colostrum and mature milk

Cell-free and cell-associated HIV-1 have been detected in both colostrum and mature breast milk of women with established HIV infection. In a study in Haiti, HIV DNA (cell-associated virus) was detected in 70% of 47 colostrum samples and about 50% of breast-milk samples obtained at 6 (n=30) and 12 (n=15) months postpartum (Ruff et al., 1994). HIV DNA was detected in 47% of 129 samples of breast milk collected 15 days after delivery, and in 20% of 96 samples collected six months after delivery (Van de Perre et al., 1993). Both studies suggest a higher level of cell associated HIV in early milk compared to later, which would reflect the relatively high level of cells in colostrum compared to mature milk.

Somewhat differently, in a study in Kenya (Nduati et al., 1995) a higher proportion of samples of milk collected between seven days and six months had HIV DNA (65% of 108 breast milk samples) than did colostrum (51% of 77 samples) (p=0. 05). Among positive samples, the proportion of infected cells ranged from less than 1 in 10 000 cells to 1 in 3. High concentrations of HIV-infected cells were more common during the period 8-90 days after delivery than in samples taken either earlier or later. A second study quantified HIV-1 RNA (measuring cell-free virus) from breast-milk supernatants collected from the same group of women at the same times (Lewis et al., 1998). The range of viral concentration in the breast-milk supernatants was very wide and, although the difference was not statistically significant, viral load tended to be higher in milk collected more than 8 days after delivery than in milk samples taken earlier (p=0.10).

The potential effect of various factors makes it difficult to draw any conclusions about the relative risk of transmission through colostrum and mature breast milk. First, colostrum and mature breast milk contain different types of cells and different levels of immune modulating components (e.g. vitamin A, immunoglobulins and lactoferrin). Second, the total volume of colostrum ingested by the infant is much smaller than that of mature breast milk. Third, the infant's immune system is less well developed during the first few days of lactation than in later lactation, while younger infants have an increased blood concentration of maternal antibodies. In the study by Tess et al. (1998b), vertical transmission was not associated with a history of colostrum intake in 148 breastfed children.

Factors associated with the risk of mother-to-child transmission

The overall risk of mother-to-child transmission is increased by a range of factors related to HIV disease, the mother, and the infant (for a comprehensive review of these factors see Newell et al., 1997). Some of these factors may also affect the risk of transmission through breast milk. Maternal risk factors include indicators of disease progression, such as high viral load, low CD4 count, and viral characteristics. The observation that the risk of transmission through breastfeeding is higher if the mother is infected postnatally (Dunn et al., 1992) suggests that the higher viral load associated with recent infection may also increase the risk of breastfeeding transmission. However, it is not clear whether viral load in blood and in breast milk are correlated. Viral load in the breast milk of postnatally infected women is an area that requires further study. Low CD4 counts have been associated with detection of HIV DNA in breast milk. A Kenyan study (Nduati et al., 1995) found a strong correlation between maternal immunosuppression (low CD4 counts) and the prevalence and concentration of breast milk HIV-1 DNA. However, knowledge of the role of maternal immunosuppression and advanced HIV disease in breast-milk transmission remains limited.

In a Malawi study of 338 women with HIV, 196 (58%) of whom were deficient in vitamin A, HIV transmission was significantly associated with vitamin A status, independent of maternal CD4 status (Semba et al., 1994). Vitamin A deficiency may increase the risk of mother-to-child HIV transmission by impairing T and B cell function, resulting in increased maternal viral load and reduced antibody concentrations. Alternatively, vitamin A deficiency could be a marker of advanced HIV disease, which may be the cause of the higher observed mother-to-child transmission rate. In a study of 72 women with CD4 counts of less than 400/ml in Nairobi (Nduati et al., 1995), vitamin A deficiency was associated with a linear increase in the prevalence of HIV-1 DNA in breast-milk cells. All six women with vitamin-A levels < 20 J_GO_KDG detectable HIV-1 DNA in their breast milk, compared to only three of eight women with vitamin-A levels at or above 40 J_GO_ Although the association between vitamin A and HIV in breast milk has been documented, no studies have been published concerning the role of vitamin A deficiency in breast-milk transmission. Vitamin A deficiency in HIV-infected women has been reported to be associated with fissured nipples (Nduati et al., 1997), which may facilitate transmission of HIV through breastfeeding. Poor breastfeeding techniques, especially poor attachment of the infant to the breast, may result in fissured nipples and hence HIV transmission may be prevented through breastfeeding counselling, and skilled help with positioning and attachment (Tess et al., 1998b; Van de Perre, 1992; Ekpini et al., 1997).

Table 3 Risk factors associated with increased overall risk of mother-to-child transmission

Strong evidence
Maternal
High viral load
Viral characteristics
Advanced disease
Immune deficiency
HIV infection acquired during
pregnancy or breastfeeding period
Obstetric
Vaginal delivery
(compared with caesarean)
Prolonged rupture of membranes
Infant
Prematurity
Breastfeeding

Limited evidence
Vitamin A deficiency
Anaemia
Sexually transmitted disease
Chorioamnionitis
Frequent unprotected sexual intercourse*
Multiple sex partners*
Smoking
Injecting drug use
Invasive procedures
Episiotomy
Lesions of skin and/or
mucous membranes (oral thrush)

*Probably due to acquisition of further virus or minor trauma

See: Review Newell et al., 1997; and Kind et al., 1998; Mandelbrot et al., 1998; Read et al., 1998; Simonds et al., 1998; Bulterys et al. 1997, Burns et al.,1997; Coll et al., 1997; Ekpini et al.1997; Greenberg et al., 1997; Kuhn et al., 1997; Maguire et al., 1997; Matheson et al., 1997; Mayaux et al., 1997; Pitt et al., 1997; Shearer et al., 1997; Thea et al., 1997; Zollner et al., 1997; Dickover et al., 1996; Guay et al., 1996; Landesman et al., 1996; Lapointe et al., 1996; Lutz-Friedrich et al., 1996; Mandelbrot et al., 1996; Rodriguez et al., 1996; Shaffer et al., 1996; Wabire-Mangen et al., 1996; Harmsen et al., 1995; Matheson et al., 1995; Mayaux et al., 1995; Ometto et al., 1995; Temmerman et al., 1995; Borkowsky et al., 1994; Boyer et al., 1994; Burns et al., 1994; Dunn et al., 1994; Kliks et al., 1994; Lallemant et al., 1994; Nduati et al., 1994; Semba et al., 1994; Thomas et al., 1994; Clerici et al., 1993; Galli et al., 1993; Jackson et al., 1993; Lepage et al., 1993; Nair et al., 1993; Roques et al., 1993; Scarlatti et al., 1993; Scarlatti, Hodara et al., 1993; St Louis et al., 1993; Van de Perre et al., 1993; Villari et al., 1993; Dunn et al., 1992; European Collaborative Study, 1992; Goedert et al., 1991; Hutto et al., 1991; Lindgren et al., 1991; Monforte et al., 1991; Hira et al., 1990; Van de Perre et al., 1991; Tovo et al., 1988.

HIV has been recovered from vaginal and cervical secretions of pregnant women (Henin et al., 1993; John et al., 1997; Loussert-Ajaka et al., 1997) and from gastric secretions of infants born to HIV-seropositive women (Ait-Khaled et al., 1997; Nielsen et al., 1996). Delivery factors that increase contact between the infant and HIV-infected maternal body fluids (cervico-vaginal secretions and blood) may therefore be the mechanism for increased risk of transmission (Read et al., 1998; European Collaborative Study, 1994). Vitamin A deficiency may also be a co-factor for increased risk associated with delivery, through impaired integrity of epithelial surfaces (Bridbord and Willoughby, 1994) and increased vaginal viral shedding (John et al., 1997, Mostad et al., 1997).

Neonatal skin and mucous membranes are ineffective barriers against infective organisms. Direct invasion of the skin and oral and gastric mucosa by HIV may play a role in transmission from mother to child, including through breast milk. Traumatic or inflammatory disruption of the skin or mucous membranes may further increase the risk of transmission (Ekpini et al., 1997; Clerici et al., 1993; European Collaborative Study, 1992; Hutto et al., 1991; Goedert et al., 1989). Disruption of the epithelial integrity of the mucous membranes of the intestine or mouth, caused by nutritional factors or infection, may increase the risk of HIV transmission through breast milk.

Factors resulting in disruption of the integrity of infants' mucous membranes, such as oral thrush, may be associated with an increased risk of breast-milk transmission (Ekpini et al., 1997; Njenga et al., 1997; European Collaborative Study, 1992).

Feeding with cow's milk, allergic reactions to complementary foods, and infectious illness can all result in intestinal damage. Because damage to the epithelial integrity of the intestine may facilitate entry of HIV, mixed feeding might be more risky for HIV transmission than exclusive breastfeeding. Infants could thus be doubly disadvantaged by being at risk of HIV transmission through simultaneous exposure to HIV through breastfeeding, and the risks related to replacement feeding. Only three studies have compared the rate of transmission in exclusively breastfed, partially breastfed and formula-fed infants (Tess et al., 1998b; Bobat et al., 1997; Ryder et al., 1991;). Although the highest transmission rate was found in exclusively breastfed infants, the lowest rate in formula-fed infants, and intermediate rates in the mixed-feeding groups, the number of exclusively formula-fed or breastfed infants in these studies was small and the differences in rates of transmission were not statistically significant.

General infections

One of the most important benefits of breast milk is its ability to protect against common childhood infections such as diarrhoea, pneumonia, neonatal sepsis and acute otitis media (Golding, 1998; Duncan et al.,1993; Goldman, 1993; Ashraf et al., 1991; Huffman et al., 1990; Lucas A., 1990; Habicht et al., 1986 & 1988; Victora et al., 1987; Hanson et al., 1985). It has been assumed, but not proven, that the breast milk of HIV-infected women also protects infants against these infections.

In a study in Kinshasa of 19 infected children, development of clinical AIDS was not associated with two particular types of infant feeding practice (Ryder et al., 1991). However, morbidity was significantly higher in 237 non-HIV-infected children (of both infected and uninfected mothers) who were not exclusively breastfed, compared with 81 uninfected infants who were exclusively breastfed during the first six months of life (Ryder et al., 1991). In Durban, South Africa, exclusively breastfed infected children had a slower rate of progression to AIDS than those on mixed feeds (Bobat et al., 1997).

Two recent studies from South Africa compared partially breastfed and exclusively formula-fed HIV-infected infants (Bobat et al., 1997; Gray et al., 1996). In these studies, both groups had similar frequencies of failure to thrive, diarrhoea, and pneumonia. Uninfected infants of HIV-positive mothers also had a comparable frequency of these conditions, whether they were partially breastfed or exclusively formula-fed. However, these results should be interpreted with great caution since the failure to detect a difference in health outcomes between breastfed and formula-fed infants may reflect factors specific to these studies. These include: short duration of exclusive breastfeeding and the inclusion of infants that had stopped breastfeeding in the breastfeeding group; a relatively safe environment (water, electricity, sanitation etc.) that minimized the risks of formula feeding; and a relatively literate, urban study population with access to continual health care, as part of a research study design. It is unlikely that these findings would be replicated in studies from other settings in sub-Saharan Africa without additional support being given to women who choose not to breastfeed.

HIV infection

Breast milk contains maternal antibodies. All basic forms of immunoglobulins IgG, IgM, IgA, IgD, and IgE are present in breast milk. The most abundant is usually secretory IgA (Lawrence, 1994). The role of HIV-specific antibodies in breast milk in inhibiting HIV transmission through breastfeeding has been investigated. Breast milk in women with established HIV infection has been found to have HIV-specific IgG, with its wide spectrum of activity against HIV proteins, comparable to HIV-specific IgG in serum. The spectrum of activity of serum IgA against HIV has been found to be similar to that of serum IgG, but the spectrum of activity of HIV-specific secretory IgA (sIgA) in breast milk is directed against only a limited number of viral proteins (env protein, gp 160, core proteins).

In a study of breast-milk samples from 215 HIV-infected women in Rwanda (Van de Perre et al., 1993), the most frequently identified HIV-specific antibody in breast milk was IgG (in >95% of samples), the next was IgM (in 41-78% of samples) and the least frequent was IgA (in 23-41% of samples). Lack of persistence of HIV-specific IgM in breast milk collected at 18 months was associated with a high risk of transmission of HIV. Of 20 children receiving breast milk with detectable HIV DNA in samples collected at day 15, but without detectable IgM in later samples, 47% were infected with HIV. In those with detectable DNA in breast milk samples at day 15, and with IgM in later samples only 30% became infected. This suggests that IgM may protect against breast-milk transmission of HIV. The rate of transmission was 18% in infants of mothers whose breast-milk sample at day 15 had undetectable HIV DNA, regardless of IgM levels (Van de Perre et al., 1993).

Other components of breast milk are protective against viral infections. Human lactoferrin has been shown in vitro to have an inhibitory activity against HIV (Harmsen et al., 1995), and lipid-dependent antiviral activity directed at HIV and other enveloped viruses and bacteria has also been described (Orloff et al., 1993; Isaacs and Thormar, 1990). An additional factor that has also been identified in breast milk, possibly a sulphated protein, glycoprotein mucin or glycosaminoglycan, appears to inhibit the binding of HIV to CD4 receptors (Newburg et al., 1992).

Primary prevention

The best way to prevent HIV infection of children through mother-to-child transmission, including transmission through breast milk, is to prevent HIV infection of young girls and women of childbearing age. In sub-Saharan Africa, Asia and the Caribbean the main mode of HIV transmission is heterosexual contact. In industrialized countries, although most women with HIV have a history of injecting drug use (IDU), or sexual partners with a history of IDU or bi-sexuality, heterosexual transmission is becoming an increasingly important route of infection (Wortley and Fleming, 1997; Gabiano et al., 1992; Holmes, 1991).

The risk of HIV infection in women is increased by such factors as immaturity of the genital tract, cervical ectopy, sexually transmitted diseases, and poor nutritional status (Mostad and Kreiss, 1996; Leroy et al., 1994; Plummer et al., 1994;). Cultural, social and economic factors also contribute to HIV transmission by increasing the vulnerability of girls and women (Ankrah et al., 1994; UNDP, 1994).

Strategies to prevent all mother-to-child transmission of HIV, including through breast-milk, should be linked to primary prevention programmes that provide education about safer sex, condoms, and diagnosis and treatment of sexually transmitted diseases, and that ensure the safety of medical procedures. HIV prevention should be emphasized for women who test seronegative in pregnancy because of the particularly high risk of MTCT if mothers are infected with HIV during pregnancy and breastfeeding.

Replacement feeding

For an HIV-infected woman to eliminate completely the risk of HIV transmission through breastfeeding she needs to feed her infant from birth with suitable replacements for breast milk (such as commercial infant formula or home-prepared formula made from modified animal milks). The range of replacement feeding options is described in HIV and infant feeding: A guide for health managers and supervisors. Currently there is little information on the safety and feasibility of using breast-milk substitutes in developing countries.

Several investigators have attempted to use mathematical models to offer guidance to policy-makers in different settings for weighing the relative risks and benefits of breastfeeding and other infant feeding methods in view of the HIV epidemic (Kuhn and Stein, 1997; Hancock et al., 1996; Nagelkerke et al., 1995; Nicoll et al., 1995; Del Fante et al., 1993; Hu et al., 1992; Heyman, 1990). These models are limited by the available data regarding the risks associated with various methods of infant feeding and their inability to consider all the factors that influence decision-making about infant feeding. In particular, although there is much evidence of the benefits of breastfeeding in reducing morbidity and mortality in infants whose mothers are not infected with HIV, currently there is little information regarding the effect of replacement feeding on infant morbidity and mortality for infants whose mothers are HIV-infected.

Where adequate replacement feeding is not possible, mothers may choose among three other strategies to reduce the risk of breast-milk transmission:

· Exclusive breastfeeding followed by early cessation of breastfeeding. Early cessation of breastfeeding may reduce exposure and hence the risk of breast milk transmission, while not eliminating the risk entirely, as the infant remains exposed for the first few months.

· Heat treatment of expressed breast milk

· Wet-nursing by a tested HIV-negative women

Early cessation of breastfeeding

Early cessation of breastfeeding reduces the risk of HIV transmission by limiting the length of time that an infant is exposed to HIV through breast milk. Women who are not able to provide adequate and hygienic replacement feeding to their infants from birth may consider this option in order to reduce the cumulative risk of longer breastfeeding duration (Leroy et al., 1998; Epkini et al., 1997; Van de Perre, 1997). It is not yet possible to specify the optimum time for cessation of breastfeeding.

Treatment of breast milk

In vitro studies have demonstrated that heat treatment of breast milk to which a known quantity of HIV had been added, using the Holder pasteurization method (at 62.5oC for 30 minutes), reduces the infectious titre of cell-free and cell-associated virus by more than five logs and six logs, respectively (Orloff et al., 1993).

As discussed earlier, breast milk contains substances that inhibit infectious agents (Goldman, 1993). Several studies have reported that HIV is inactivated when milk is left to stand at room temperature for half an hour (Orloff et al., 1993; Newburg et al., 1992; Isaacs and Thormar, 1990). In the first two of these studies, the inhibitory effects of breast milk were attributed to a milk-lipase-activated factor that released fatty acids which were thought to dissolve or disrupt the viral envelope. Newburg et al demonstrated that human milk glycosaminoglycans inhibit binding of HIV glycoprotein gp120 to host cell CD4 receptors. There is a need to evaluate alternatives for treating breast milk, which utilize or enhance the action of naturally occurring anti-HIV factors to prevent breast-milk transmission of HIV.

However, all strategies to modify or treat breast milk to render it non-infectious would involve expressing milk, and some women may find it difficult to sustain this process for long periods of time. This should not prevent the option being offered, and professional support should be provided when women choose it. Expression and heat treatment may also be a temporary solution during periods of increased transmission risk, as in cases of cracked nipples or breast abscess, and for low-birth-weight or sick infants for whom the risk of artificial feeding is greater.

Heat treatment of breast milk is recommended for all milk banks, which should also screen milk donors for HIV.

Wet-nursing by a tested HIV-negative woman

In communities where wet-nursing by a family member is practised this option can be considered. It will be necessary for the wet-nurse to agree to and understand the implications of voluntary HIV counselling and testing (VCT). She would also have to be counselled about HIV and be able to avoid becoming infected during breastfeeding.

Antiretroviral therapy

The use of AZT (zidovudine) during the second and third trimester in pregnant women and in infants during the first six weeks of life, in the absence of breastfeeding, can reduce mother-to-child transmission of HIV by two-thirds (Connor et al., 1994). A "short course" regimen of AZT (after 36 weeks gestation and without the neonatal component), combined with formula feeding, has recently been shown in Thailand to reduce mother-to-child HIV transmission by half (Centers for Disease Control, 1998). The latter approach may be more feasible where women present late for prenatal care, or where health service resources are limited. Further reductions in mother-to-child HIV transmission may be possible with the use of a combination of antiretroviral drugs (Bryson, 1996), which are currently being evaluated in clinical trials in both breastfeeding and non-breastfeeding populations (Fowler, 1997).

The effectiveness of AZT in reducing mother-to-child transmission has been demonstrated only in non-breastfed infants. It is currently not known to what extent infants who have escaped infection during pregnancy and delivery, following prophylactic therapy in their mothers with AZT, are at risk of becoming infected subsequently through breastfeeding. However, it is likely that antiretroviral therapy around the time of delivery will not be as effective if the infant is then exposed through breastfeeding. Since many HIV-infected mothers may face obstacles to replacement feeding - for example stigma, affordability, risk to the infant of other infections and malnutrition - the effectiveness of antiretroviral treatment of breastfeeding mothers/or breastfed infants, with and without a postnatal treatment component, is an important research question. Several trials are under way, in populations where breastfeeding is the norm, to evaluate various AZT regimens, combination therapy using two antiretrovirals (AZT with 3TC), and Nevirapine (Fowler, 1997). Results of these and other trials will be available by mid-1999. It is important for this information to be available before policies are adopted which introduce antiretroviral therapy to reduce the risk of mother-to-child transmission in situations where infant feeding choices are limited.

Summary and Conclusion

Current scientific evidence provides the basis for the following statements and suggests areas where additional research is required.

Mother-to-child transmission of HIV

· The overall risk of mother-to-child transmission of HIV is about 15-25% among seropositive women who do not breastfeed (in the absence of interventions to reduce the likelihood of transmission), and between 25-45% among women who breastfeed.

HIV can be transmitted through breast milk

· The virus has been detected in components of breast milk.

· HIV infection has been found in infants of mothers who became infected with HIV during the breastfeeding period.

· Infants of HIV-negative mothers have been infected through exposure to HIV in unpasteurized breast milk from unscreened donors and HIV-infected wet-nurses.

· Infants diagnosed as HIV-negative at three months of age or later have been infected subsequently, with breastfeeding being the only risk factor.

Breastfeeding can be an important mode of mother-to-child transmission of HIV

· Where the mother has established HIV infection, the overall additional risk of HIV transmission during breastfeeding is at least 15%.

· In populations where breastfeeding is the main method of infant feeding, approximately one third of paediatric HIV is due to breast-milk transmission.

The mechanisms of breast-milk transmission are not yet fully understood

· The respective roles of cell-free and cell-associated HIV in breast-milk transmission are not known, nor is the association between plasma and milk virus levels understood.

· The portal of entry for the virus via infant mucosa requires further investigation.

Certain factors may increase the risk of HIV transmission through breast milk

· When a mother has been recently infected with HIV, the risk of transmission through breastfeeding may be twice as high as that of a women whose infection is already established (29% compared with 15%). This is probably due to high viral load occurring with recent infection. However, it is not clear whether a high serum viral load is correlated with a high viral load in breast milk. Further research is required.

· Increased risk of mother-to-child transmission is associated with markers of advanced HIV infection and maternal immunosuppression, including plasma viral load, clinical symptoms, and low CD4 and high CD8 cell counts. However, current knowledge about the role of maternal immunosuppression and advanced HIV disease in breast-milk transmission is limited and requires further investigation.

· Vitamin A deficiency is associated with an increased risk of overall mother-to-child transmission and with HIV in breast milk, but no studies have confirmed the role of vitamin A deficiency in increasing the risk of transmission through breastfeeding. Vitamin A supplementation has not been proved to be effective in reducing MTCT.

· Disruption of the epithelial integrity of the mucous membranes of the infant mouth or intestine (caused by nutritional or infectious factors such as mixed feeding and oral thrush), and nipple fissures may play a role in increasing the risk of transmission through breastfeeding. Research in this area continues.

· The effect on HIV transmission due to breastfeeding of giving AZT during pregnancy and delivery is not known, nor is the effect of postnatal treatment of breastfed infants with ARVs. Research is being carried out and results will be available in 1999.

Transmission can take place at any point during breastfeeding

· The risk of breast-milk transmission of HIV appears to be cumulative. The longer the duration of breastfeeding, the greater the additional risk of HIV transmission through breast milk.

· Because it is not known whether the risk of transmission differs at different times during lactation, the degree of efficacy resulting from early cessation of breastfeeding cannot be predicted.

· HIV has been detected in colostrum and mature breast milk; however, based on current evidence, it is not possible to establish the relative risks of transmission through colostrum and breast milk.

· Currently available diagnostic tools are inadequate for estimating risk associated with breastfeeding in the first few months of life. The risk of late postnatal transmission through breastfeeding is estimated to be 4-12%. This may possibly account for about half of transmission through breastfeeding.

The anti-infective properties of breast milk in the context of HIV

· HIV-positive women who breastfeed infants who are already infected with HIV may provide some protection against common childhood infections. Further research is required.

· Anti-infective substances in the breast milk of HIV-infected women, including immunoglobulins, lactoferin, and mucins, may target HIV, but further studies are needed to investigate the correlation between risk of transmission and the presence or absence of these substances.

The safety of different methods of infant feeding

· There is very little information on the safety and feasibility of infant-feeding alternatives for seropositive mothers and these aspects need to be studied (including commercial infant formula, homemade infant formula, heat-treated expressed breast milk, and wet-nursing). It is also important to identify approaches to treating expressed breast milk to eliminate the risk of transmission while preserving the milk's nutritional content.

· It is important to determine the efficacy of antiretroviral therapy given to the mother or the child during the breastfeeding period.

· Little is known about the effect of different feeding methods, including mixed feeding, on the course of HIV infection and other health outcomes in HIV-infected children.

Finally, research is needed on the effect of breastfeeding on the nutritional and immune status of the mother. The benefits of breastfeeding may be different for women infected with HIV.

References

Adjorlolo-Johnson G, De Cock KM, Ekpini E, et al. Prospective comparison of mother-to-child transmission of HIV-1 and HIV-2 in Abidjan, Ivory Coast. JAMA 1994;272:462-466.

Ait-Khaled M, Lyall EGH, Stainsby C, Taylor GP, et al. Intrapartum mucosal exposure to human immunodeficiency virus type 1 of infants born to HIV-1-infected mothers correlates with maternal plasma virus burden. Journal of Infectious Diseases 1998;177:1097-1100

Akr, ed. Infant feeding: the physiological basis. Bulletin of the World Health Organization, 1990; 67 (Supplement).

American Academy of Pediatrics Policy Statement. Breastfeeding and the Use of Human Milk. Pediatrics. 1997; 100 (6): 1035-1039.

Amerongen HM, Weltzin R, Farnet CM, Michetti P, Haseltine WA, Neutra MR. Transepithelial transport of HIV-1 by intestinal M cells: a mechanism for transmission of AIDS. J Acquir Immune Defic Synd 1991;4:760-765

Andreasson PA, Dias F, Naucler A, Andersson S, Biberfeld G. A prospective study of vertical transmission of HIV-2 in Bissau, Guinea-Bissau. AIDS 1993;7:989-993.

Ankrah ME, Mhloyi MM, Manguyu F, Nduati RW. Women and children and AIDS. In: Essex M, Mboup S, Kanki PJ, Kalengayi MR. AIDS in Africa. Raven Press, Ltd. , New York 1994.

Ashraf RN, Jalil F, Zaman S, Karlberg J, et al. Breastfeeding and protection against neonatal sepsis in a high risk population. Archives of Diseases in Childhood 1991;66:488-490.

Baba TW, Kock J, Mittler M, et al. Mucosal infection of neonatal rhesus monkeys with cell-free SIV. AIDS Research and Human Retroviruses 1994;10:351-357.

Bertolli J, St. Louis, Simonds RJ, et al. Estimating the timing of mother-to-child transmission of human immunodeficiency virus in a breastfeeding population in Kinshasa, Zaire. Journal of Infectious Diseases 1996;174:722-726.

Blanche S, Rouzioux C, Moscatao M-LG, et al. A prospective study of infants born to women seropositive for human immunodeficiency virus type 1. N Engl J Med 1989;320:1643-1648.

Bobat R, Moodley D, Coutsoudis, Coovadia H. Breastfeeding by HIV-1 infected women and outcome in their infants: a cohort study from Durban, South Africa. AIDS 1997;11:1627-1633.

Bomsel M. Transcytosis of infectious human immunodeficiency virus across a tight human epithelial cell line barrier. Nat Med 1997; 3:42-47

Borkowsky W, Krasinski K, Yunzhen C, et al. Correlation of perinatal transmission of human immunodeficiency virus type 1 with maternal viraemia and lymphocyte phenotypes. Journal of Pediatrics 1994;125:345-51.

Boyer PJ, Dillon M, Navaie M, et al. Factors predictive of maternal fetal transmission of HIV-1: preliminary analysis of AZT given during pregnancy and/or delivery. JAMA 1994; 271:1925-1930.

Bridbord K, Willoughby A. Vitamin A and mother-to-child transmission. Lancet 1994; 343:1585-1586.

Bryson YJ, Luzuriaga K, Wara DW. Proposed definitions for in utero versus intrapartum transmission of HIV-1. N Engl J Med 1992;327:1246-1247.

Bryson YJ. Perinatal HIV-1 transmission: recent advances and therapeutic interventions. AIDS 1996;10 (Supplement):S33-S42.

Bulterys M, Landesman S, Burns DN, Rubinstein A and Goedert JJ. Sexual behaviour and injection drug use during pregnancy and vertical transmission of HIV-1. J of Acquir Immune Defic Syndr Human Retrovir 1997;15: 76-82.

Burns DN, Landesman S, Muenz LR, et al. Cigarette smoking, premature rupture of membranes, and vertical transmission of HIV-1 among women with low CD4+ levels. J Acquir Immune Defic Syndr 1994;7:718-726.

Burns DN, Landesman S, Wright DJ, et al. Influence of other maternal variables on the relationship between maternal viral load and mother-to-infant transmission of human immunodeficiency virus type 1. Journal of Infectious Disease, 1997;175:1206-1210.

Centers for Disease Control. Administration of zidovudine during late pregnancy and delivery to prevent perinatal HIV transmission, Thailand, 1996-1998. MMWR 1998;7(8):151-154.

Clerici M, Sison AV, Berzofsky JA, et al. Cellular immune responses associated with mother- to-child transmission of HIV. AIDS 1993;7:1427-1433.

Colebunders R, Kapita B, Nekwei W, et al. Breastfeeding and transmission of HIV. Lancet 1988;2:1487.

Coll O, Hernandez M, Boucher CA, et al. Vertical HIV-1 transmission correlates with a high maternal viral load at delivery. J Acquir Immune Defic Syndr Human Retrovirol 1997;14:26-30.

Connor EM, Sperling RS, Gelber R, et al. Reduction of maternal-infant transmission of human immunodeficiency virus type 1 with zidovudine treatment. N Engl J Med 1994;331:1174-1179.

Dabis F, Msellati P, Dunn D, et al. Estimating the rate of mother-to-child transmission of HIV. Report of a workshop on methodological issues, February 1992, Ghent, Belgium. AIDS 1993;7:1139-1148.

Datta P, Embree JE, Kreiss JK, et al. Mother-to-child transmission of human immunodeficiency virus type 1: report from the Nairobi study. Journal of Infectious Diseases 1994;170:1134-1140.

Del Fante P, Jenniskens F, Lush L, et al. HIV, breastfeeding and under-five mortality: modelling the impact of policy decisions for or against breastfeeding. Journal of Tropical Medicine and Hygiene 1993;96:203-211.

De Soyza I, Rea M, Martines J, Why promote breastfeeding in diarrhoeal disease control programmes? Health Policy and Planning. 1991; 6 (4): 371-379.

Dickover RE, Garratty EM, Herman SA, et al. Identification of levels of maternal HIV-1 RNA associated with risk of perinatal transmission: effects of maternal zidovudine on viral load. JAMA 1996;275:599-605.

Duncan B, Ey J, Holberg CJ, et al Exclusive breastfeeding for at least 4 months protects against otitis media. Pediatrics. 1993; 91:867-872.

Dunn DT, Newell ML, Ades AE, Peckham C. Risk of human immunodeficiency virus type 1 transmission through breastfeeding. Lancet 1992;340:585-588.

Dunn DT, Newell ML, Mayaux MJ, Kind C, Hutto C, Goedert JJ, Andiman W, and Perinatal AIDS Collaborative Transmission Studies. Mode of Delivery and Vertical Transmission of HIV-1: A Review of Prospective Studies. J Acquir Immune Def Syndr 1994;7:1064-1066

Ekpini E, Wiktor SZ, Satten GA, et al. Late postnatal transmission of HIV-1 in Abidjan, Cote d'Ivoire. Lancet 1997;349:1054-1059.

European Collaborative Study. Risk factors for mother-to-child transmission of HIV-1. Lancet 1992;339:1007-1012.

European Collaborative Study. Caesarean section and risk of transmission of HIV-1 infection. Lancet 1994;343:1464-1467

Featherstone C. M cells: portals to the mucosal immune system. Lancet 1997;350:1230.

Fleming SC, Kapembwa MS, MacDonald TT, Griffin GC. Direct in vitro infection of human intestine with HIV-1. AIDS 1992;6:1099-1104.

Fowler MG. Update on international trials to prevent HIV transmission from mothers to infants. Conference on Global Strategies for the Prevention of HIV Transmission from Mothers to Infants. Edited by Martin N and Amman AJ, September 1997, Washington,DC; 177-180.

Gabiano C, Tovo P-A, de Martino M, et al. Mother-to-child transmission of human immunodeficiency virus type 1: Risk of infection and correlates of transmission. Paediatrics 1992;90:369-374.

Galli L, Tovo P-A, Martino M, et al. Impact of infection status in the father on the rate of HIV-1 transmission from and infected mother to her child. Paediatric AIDS and HIV Infection: Fetus to Adolescent 1993;4:425-428.

Goedert JJ, Duliege AM, Amos CI, et al. Higher risk of HIV infection for first born twins. Lancet 1991;338:1471-1475.

Goedert JJ, Mendez H, Drummond JE, et al. Mother-to-infant transmission of human immunodeficiency virus type 1: association with prematurity or low anti-gp120. Lancet, 1989; i:1351-1355.

Golding J, Emmett PM, Rogers IS, Breastfeeding and infant mortality Early Human Development . 1997; 49 Suppl. S143-S155. .

Goldman A. The immune system of human milk: antimicrobial, antiinflammatory and immunomodulating properties. Pediatr Infect Dis J 1993;12:664-671.

Gray G, McIntyre JA, Lyons SF. The effect of breastfeeding on vertical transmission of HIV-1 in Soweto, South Africa. XI International Conference on AIDS. Vancouver, July 1996 Abstract ThC415.

Greenberg BL, Semba RD, Vink P et al. Vitamin A deficiency and maternal-infant transmission of HIV in two metropolitan areas in the United States. AIDS, 1997;11:325-332

Guay LA, Hom DL, Mmiro F, et al. Detection of human immunodeficiency virus type 1 DNA and p24 antigen in breast milk of HIV-1 infected Ugandan women and vertical transmission. Paediatrics 1996;98:438-444.

Habicht JP, DaVanzo J, Butz W. Does breastfeeding save lives or are apparent benefits due to biases? American Journal of Epidemiology 1986;123:279-289.

Habicht J-P, DaVanzo J, Butz WP, Mother's Milk and Sewage: Their Interactive Effects on Infant Mortality. Pediatrics. 1988; 81: 456-61.

Hancock J, Nalo DS, Aoko M, Mutemi R, Clark H, Forsythe S. The macroeconomic impact of HIV/AIDS. In: AIDS in Kenya: Socioeconomic impact and policy implications. Family Health

International/AIDSCAP, 1996.

Hanson LA, Hofvander Y, Lindquist B, Zetterstrom R. Breastfeeding as a protection against gastroenteritis and other infections. Acta Paediatr Scand 1985;74:641-642.

Harmsen MC, Swart PJ, de Bethune MP. Antiviral effects of plasma and milk proteins: Lactoferrin shows potent activity against both human immunodeficiency virus and human cytomegalovirus replication in vitro. Journal of Infectious Disease 1995;172:380-388.

Henin Y, Mandelbrot L, Henrion R, Pradinaud R, Coulaud JP, Montagnier L. Virus excretion in the cervicovaginal secretions of pregnant and nonpregnant HIV-infected women. J Acquir Immune Defic Synd 1993;6:72-75

Heyman SJ. Modelling the impact of breastfeeding by HIV-infected women on child survival. American Journal of Public Health 1990;80:1305-1309

Hira SK, Mangrola UG, Mwale C, et al. Apparent vertical transmission of human immunodeficiency virus type 1 by breastfeeding in Zambia. Journal of Pediatrics 1990; 117: 421-424.

Holmes KK. The changing epidemiology of HIV transmission. Hospital Practice 1991; November 15:153-177.

Hu DJ, Heyward WL, Byers RH, et al. HIV infection and breastfeeding: policy implications through a decision analysis model. AIDS 1992;6:1505-1513.

Huffman SL, Combest C. Role of breastfeeding in the prevention and treatment of diarrhoea. Journal of Diarrhoeal Diseases Research 1990;8(3):68-81.

Hutto C, Wade PP, Shenghan L, et al. A hospital-based prospective study of perinatal infection with human immunodeficiency virus type 1. Journal of Pediatrics 1991;118:347-53.

Isaacs CE, Thormar H. Human milk lipids inactivate enveloped viruses. In: Atkinson SA, Hanson LA, Chandra RK. Breast feeding, Nutrition Infections and Infant Growth in Developed and Emerging Countries. ARTS Biomedical publishers and Distributors, St John, Newfoundland, Canada, 1990.

Jackson JB, Kataaha P, Hom DL, et al. B-2 microglobulin, HIV-1 p24 antibody and acid dissociated HIV-1 p24 antigen levels; predictive markers for vertical transmission of HIV-1 in pregnant Ugandan women. AIDS 1993;7:1475-1479.

John GC, Nduati RW, Mbori-Ngacha D, et al. Genital shedding of human immunodeficiency virus type 1 DNA during pregnancy: Association with immunosupression, abnormal cervical and vaginal discharge and severe vitamin A deficiency. Journal of Infectious Disease 1997;175:57-62.

Karlsson K, Massawe A, Urassa E et al. Late postnatal transmission of human immunodeficiency virus type 1 infection from mothers to infants in Dar es Salaam, Tanzania. Pediatr Infect Dis J 1997;16:963-967

Kind C, Rudin C, Siegrist CA, et al. Prevention of vertical HIV transmission: additive protective effect of elective caesarean section and zidovudine prophylaxis. AIDS 1998;12:205-210

Kliks SC, Wara DW, Landers DV, Levy JA. Features of HIV-1 that could influence maternal-child transmission. JAMA 1994;272:467-474.

Kuhn L, Abrams EJ, Matheson PB, et al. Timing of maternal-infant transmission: associations between intrapartum factors and early polymerase chain reaction results. AIDS 1997;11:429-435.

Kuhn L, Stein Z. Infant survival, HIV infection and feeding alternatives in less developed countries. American Journal of Public Health 1997;87:926-931.

Lallemant M, Le Coeur S, Samba L, et al. Mother-to-child transmission of HIV-1 in Congo central Africa. AIDS 1994;8:1451-1456.

Lallemant M, Baillou A, Le Coeur S. Maternal antibody response at delivery and perinatal transmission of human immunodeficiency virus type 1 in African women. Lancet 1994;343:1001-1005.

Landesman SH, Kalish LA, Burns DN, et al. Obstetrical factors and the transmission of human immunodeficiency virus type 1 from mother to child. N Engl J Med 1996;334:1617-1623.

Lapointe N, Samson J, Bazet A, Boucher M, Fauvel M, Tran T, et al. Mother-to-child transmission associated with duration of the second stage of labour. XI International Conference on AIDS. Vancouver, July 1996 Abstract C340.

Lawrence R. Breastfeeding: a guide for the medical profession, 4th edition. St. Louis: Mosby, 1994.

Lepage P, Van de Perre P, Carael M, et al. Postnatal transmission of HIV from mother to child. Lancet 1987;ii:400.

Lepage P, Van de Perre, Msellati P, et al. Mother-to-child transmission of human immunodeficiency virus type (HIV-1) and its determinants: a cohort study from Kigali, Rwanda. American Journal of Epidemiology 1993;137:589-599.

Leroy V, Newell ML, Dabis F. International multicentre pooled analysis of late postnatal mother-to-child transmission of HIV infection. Lancet 1998;352:597-600.

Leroy V, Van de Perre P, Lepage P, et al. Seroincidence of HIV-1 infection in African women of reproductive age: a prospective cohort study in Kigali, Rwanda, 1988-1992. AIDS 1994;8:983-936.

Lewis P, Nduati R, Kreiss JK, John GC, et al. Cell-free human immunodeficiency virus type 1 in breast milk. Journal of Infectious Disease 1998;177:7-11.

Lindgren S, Anzen B, Bohlin AB, Lidman K. HIV and child-bearing: clinical outcome and aspects of mother-to-child transmission. AIDS 1991;5:1111-1116.

Loussert-Ajaka I, Mandelbrot L, Delmas MC, et al. HIV-1 detection in cervicovaginal secretions during pregnancy. AIDS 1997;11:1575-1581.

Lucas A, Cole TJ, Breastmilk and neonatal necrotising enterocolitis. Lancet. 1990; 336: 1519-1523.

Lutz-Friedrich R, Grubert TA, Dathe O, et al. QC-PCR quantitation of HIV-1 plasma RNA level during pregnancy: a new prognostic marker for vertical transmission. XI International Conference on AIDS. Vancouver, July 1996, Abstract TuC 2578.

Maguire A, Sanchez E, Fortuny C, et al. Potential risk factors for vertical HIV-1 transmission in Catalonia, Spain: the protective role of caesarean section. AIDS 1997;11:1852-7.

Mandelbrot L, Brossard Y, Aubin JT, et al. Testing for in utero human immunodeficiency virus infection with fetal blood sampling. Am J Obstet Gynecol 1996;175:489-493.

Mandelbrot L, Mayaux MJ, Bongain A, et al. Obstetric factors and mother-to-child transmission of HIV type 1: the French perinatal cohorts. Am J Obstet Gynecol 1996;175:661-667.

Mandelbrot L, Le Chenadec J, Berrebi A, et al. Perinatal HIV-1 transmission: interaction between ziduvodine prophylaxis and mode of delivery in the French perinatal cohort. JAMA 1998;280:55-60.

MAP. Monitoring the AIDS epidemic (MAP) network. The status and trends of the HIV/AIDS/STD epidemics in the world. Provisional report, June 1998.

Matheson PB, Weedon J, Cappelli M, et al. Comparison of methods of estimating the mother- to-child transmission rate of human immunodeficiency virus type 1 (HIV-1). American Journal of Epidemiology 1995;142:714-718.

Matheson PB, Thomas PA, Abrams EJ et al. Heterosexual behaviour during pregnancy and perinatal transmission of HIV-1. AIDS, 1997; 10:1249-1256

Mayaux MJ, Blanche S, Rouzioux C, et al. Maternal factors associated with perinatal HIV-1 transmission: the French cohort study: 7 years of follow-up observation. The French Pediatric HIV Infection Study Group. J Acquir Immune Defic Syndr Human Retrovirol 1995; 8:188-194.

Mayaux MJ, Dussaix E, Isopet J et al. Maternal virus load during pregnancy and mother-to-child transmission of human immunodeficiency virus type 1: the French perinatal cohort study. Journal of Infectious Disease 1997;175:172-175.

Monforte AA, Ravizza M, Muggiasca ML, et al. Maternal predictors of HIV transmission. European Journal of Obstetrics and Gynaecology and Reproductive Biology 1991;42:131-136.

Monteiro CA., Can infant mortality be reduced by promoting breastfeeding? Evidence from Sao Paulo City. Health Policy and Planning 1990; 5: 23-29.

Morgan G, Wilkins HA, Pepin J, Ousman J, Brewster D, Whittle H, et al. AIDS following mother-to-child transmission of HIV-2. AIDS 1990;4:879-882.

Mostad SB, Overbaugh J, DeVange DM, et al. Hormonal contraception, vitamin A deficiency, and other risk factors for shedding of HIV-1 infected cells from the cervix and vagina. Lancet 1997;350:922-27.

Mostad SB, Kreiss JK. Shedding of HIV-1 in the genital tract. AIDS 1996;10:1305-1315.

Msellati P., Newell M-L., Dabis F., Rates of mother-to-child transmission of HIV-1 in Africa, America and Europe: Results from 13 perinatal studies Journal of Acquired Immune Deficiency Syndromes 1995;8:506-510.

Nagelkerke NJO, Moses S, Embree JE, et al. The duration of breastfeeding of HIV-1 infected mothers in developing countries: balancing benefits and risks. AIDS 1995;8:176-181.

Nair P, Alger L, Hines S, et al. Maternal and neonatal characteristics associated with HIV infection in infants of seropositive women. Journal of Acquired Immune Deficiency Syndromes 1993;6:298-302.

Nduati R, John G, Kreiss J. Postnatal transmission of HIV-1 through pooled breast milk. Lancet 1994;344:1432.

Nduati R, John G, Richardson B, et al. Human immunodeficiency virus type-1 infected cells in breast milk: Association with immunosupression and vitamin A deficiency. Journal of Infectious Disease 1995;172:1461-1468.

Nduati R, John GC, Mbori-Ngacha DA, et al. Breast disease among lactating HIV-1 infected women. Xth ICASA. Abidjan, 1997.

Nesheim SR, Lindsay M, Sawyer MK, et al. A prospective population-based study of HIV perinatal transmission. AIDS 1994;8:1293-1298.

Newburg DS, Viscidi RP, Ruff A, Yolken RH. A human milk factor inhibits binding of human immunodeficiency virus to the CD4 receptor. Paediatric Research 1992;31:22-28.

Newell ML. Mechanisms and timing of mother-to-child transmission of HIV-1. AIDS 1998;12:831-837

Newell ML, Gray G, Bryson YJ. Prevention of mother-to-child transmission of HIV-1 infection. AIDS 1997;11 (suppl A): S165-172

Njenga S, Ombree JE, Ndinya-Achola, et al. Risk factors for postnatal mother-to-child transmission of HIV in Nairobi. Conference on Global Strategies for Prevention of HIV Transmission from Mothers to Infants, September 1997, Washington DC.

Nicoll A, Newell M-L, Van Praag E, Van de Perre P, Peckham C. Infant feeding policy and practice in the presence of HIV-1 infection. AIDS 1995;9:107-119.

Nielsen K, Boyer P, Dillon M, et al. Presence of human immunodeficiency virus type 1 and HIV-1-specific antibodies in cervicovaginal secretions of infected mothers and in the gastric aspirates of their infants. Journal of Infectious Diseases 1996;173:1001-1004.

Ometto L, Zanotto C, Maccabruni A, et. al. Viral phenotype and host-cell susceptibility to HIV-1 infection as risk factors for mother-to-child transmission. AIDS 1995;:427-434.

Orloff SL, Wallingford JC, McDougal JS. Inactivation of human immunodeficiency virus type 1 in human milk: effects of intrinsic factors in human milk and of pasteurization. Journal of Human Lactation 1993;9:13-17.

Palasanthiran P, Ziegler JB, Stewart GJ, et al. Breastfeeding during primary maternal immunodeficiency virus infection and risk of transmission from mother to infant. Journal of Infectious Disease 1993;167:441-444.

Pitt J, Brambilla D, Reichelderfer P, et al. Maternal immunologic and virologic risk factors for infant human immunodeficiency virus type 1 infection: findings from the women and infants transmission study. Journal of Infectious Disease 1997;175:57-75.

Plummer FA, Tyndall MW, Ndinya-Acholla J, Moses S. Sexual transmission of HIV and the role of sexually transmitted diseases. In: Essex M, Mboup S, Kanki PJ, Kalengayi MR. AIDS in Africa. New York: Raven Press, Ltd. , New York, 1994.

Read J. Mode of delivery and vertical transmission of HIV-1: a meta-analysis from fifteen prospective cohort studies (The International Perinatal HIV Group). XII International Conference on AIDS. Geneva, July 1998 Abstract 23603.

Rodriguez E, Mofenson L, Chang BH, et al. Association of maternal drug use during pregnancy with maternal HIV culture positivity and perinatal HIV transmission. AIDS 1996; 10: 273-282.

Roques P, Marce D, Courpotin C, et al. Correlation between HIV provirus burden and in utero transmission. AIDS 1993;7 (Supplement):S39-S43.

Rouzioux C, Costalgliola D, Burgand M, et al. Estimated timing of mother-to-child human immunodeficiency virus type 1 (HIV-1) transmission by use of a Markov model. Am J Epidemiol 1995;142:1330-1337

Ruff A, Coberly J, Halsey N, et al, Prevalence of HIV-1 DNA and P24 antigen in breast milk and correlation with maternal factors. Journal of Acquired Immune Deficiency Syndrome 1994;7:68-72.

Ryder RW , Nsuami M, Nsa W, et al. Mortality in HIV-1 seropositive women, their spouses, and their newly born children during 36 months of follow-up in Kinshasa, Zaire. AIDS 1994;8:667-672.

Ryder RW, Behets F. Reasons for wide variation in reported rates of mother-to-child transmission of HIV-1. AIDS 1994;8:1495-1497.

Ryder RW, Manzila T, Baende E, et al. Evidence from Zaire that breastfeeding by HIV seropositive mothers is not a major route for perinatal HIV-1 transmission but does decrease morbidity. AIDS 1991; 5:709-714.

Scarlatti G, Leitner T, Halapi E, et al. Comparison of variable region 3 sequences of human immunodeficiency virus type 1 from infected children with the RNA and DNA sequences of the viral population of their mothers. Proc Natl Acad Sci 1993;90:1721-1725.

Scarlatti G, Hodara V, Rossi P, et al. Transmission of human immunodeficiency virus type I (HIV-1) from mother to child correlates with viral phenotype. Virology 1993;197:624-629.

Sellon RK, Jordan HL, Kennedy-Stokskopf SK, Tompkins MB, Tompkins WAF. Feline immunodeficiency virus can be experimentally transmitted via milk during acute maternal infection. Virology 1994;8:3380-3385.

Semba RD, Miotti PG, Chiphangwi JD, et al. Maternal vitamin A deficiency and mother-to- child transmission of HIV-1. Lancet 1994;343:1593-1597.

Shaffer N, Bhiraleus P, Chinayon P, et al. High viral load predicts perinatal HIV-1 subtype E transmission, Bangkok, Thailand. XI International Conference on AIDS. Vancouver, July 1996 Abstract TuC 343.

Shearer WT, Quinn TC, LaRussa P, et al. Viral load and disease progression in infants infected with human immunodeficiency virus type 1. N Engl J Med 1997;336:1337-1342.

Simonds RJ, Steketee R, Nesheim S, et al. Impact of ziduvodine use on risk and risk factors for perinatal transmission of HIV: Perinatal AIDS Collaborative Transmission Studies. AIDS 1998;12:301-308.

Simonon A, Lepage P, Karita E, et al. An assessment of the timing of mother-to-child transmission of human immunodeficiency virus type 1 by means of polymerase chain reaction. Journal of Acquired Immune Deficiency Syndromes 1994;7:952-957.

St Louis M, Munkolenkole K, Brown C, et al. Risk for perinatal HIV-1 transmission according to maternal immunologic, virologic and placental factors. JAMA1993;269:2853-2859.

Stiehm R, Vink P. Transmission of human immunodeficiency virus infection by breastfeeding. Journal of Pediatrics 1991;118:410-12.

Taha T, Miotti P, Kumwenda N, et al. HIV infection due to breastfeeding in a cohort of babies not infected at enrolment. XII International Conference on AIDS. Geneva, July 1998 Abstract 23270.

Temmerman M, Nyong'o AO, Bwayo J, et al. Risk factors for mother-to-child transmission of human immunodeficiency virus 1 infection. Am J Obstet Gynecol 1995;172:700-705.

Thapa S, Short RV, Pott M. Breastfeeding, birth spacing and their effects on child survival. Nature 1989;335:679-682

The Working Group on Mother-to-Child Transmission of HIV. Rates of mother-to-child transmission of HIV-1 in Africa, America and Europe: Results from 13 perinatal studies. J Acquir Immune Defic Syndr Human Retrovirol 1995;8:506-510.

Thea DM, Steketee RW, Pliner V, et al. The effect of maternal viral load on the risk of perinatal transmission of HIV-1. AIDS 1997;11:437-444.

Tess BH, Rodrigues LC, Newell ML, et al. Breastfeeding, genetic, obstetric and other risk factors associated with mother-to-child transmission of HIV-1 in Sao Paulo State, Brazil. AIDS 1998a;12:513-520.

Tess BH, Rodrigues CL, Newell ML, et al. Infant feeding and risk of mother-to-child transmission of HIV-1 in Sao Paulo State, Brazil. J Acquir Immun Defic Synd 1998b;19:189-194

Thomas PA, Weedon J, Kraskinski K, et al. Maternal predictors of perinatal HIV transmission. Pediatric Infectious Disease Journal 1994;13:489-495.

Tovo PA, De Martino M, Caramia G, et al. Epidemiology, clinical features, and prognostic factors of paediatric HIV infection. Lancet 1988; ii:1043 -1046.

UNAIDS. Report on the Global HIV/AIDS epidemic. Geneva: UNAIDS, 1998.

UNDP. Young women: silence, susceptibility and the HIV epidemic. (Editorial) Paediatric AIDS and HIV infection: fetus to adolescent 1994;5:1-9.

Van de Perre P, Simonon A, Msellati P, et al. Postnatal transmission of human immunodeficiency virus type 1 from mother to infant. A prospective cohort study in Kigali, Rwanda. N Engl J Med 1991;325:593-598.

Van de Perre P, Simonon A, Hitimana D, et al. Infective and anti-infective properties of breastmilk from HIV-1-infected women. Lancet 1993;341:914-918.

Van de Perre P, Hitimana DG, Simonan A, et al. Postnatal transmission of HIV-1 associated with breast abscess. Lancet 1992;339:1490-1491

Van de Perre P, Meda N, Cartoux M, Leroy V, Dabis F. Late postnatal transmission of HIV-1 and early weaning. Lancet 1997;350(9072):221.

Victora CG, Vaughan JP, Lombardi C, Fuchs SM, Gigante LP, Smith PG, Nobre LC, Teixeira AMB, Moreira LB, Barros, FC. Evidence for protection by breastfeeding against infant deaths from infectious diseases in Brazil. The Lancet 1987 (ii): 319-322.

Villari P, Spino C, Chalmers TC, et al. Caesarian section to reduce perinatal transmission of human immunodeficiency virus. On-line J Curr Clin Trials 1993;2:July 8 Document no. 4.

Wabire-Mangen F, Gray RH, Mmiro FA, et al. Placental risk factors for the vertical transmission of HIV-1 in Uganda. XI International Conference on AIDS. Vancouver, July 1996 Abstract TuC341.

World Development Report: Investing in health. World Development Report, Oxford University Press. 1993.

Wortley PM, Fleming PL. AIDS in women in the United States, recent trends. JAMA 1997;278:911-916.

Ziegler JB, Johnson RO, Cooper D, Gold J. Postnatal transmission of AIDS-associated retrovirus from mother to infant. Lancet 1985;i:896-898.

Zollner B, Feucht H-H, Helling-Giese G, et al. Threshold of HIV-1 copy numbers for vertical transmission. AIDS 1997;11:542-3.