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close this book Opportunities for Control of Dracunculiasis (1982)
close this folder Overview of Dracunculiasis
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Overview of Dracunculiasis

Dracunculiasis is a parasitic infection caused by a long, stringlike, female worm--the nematode Dracunculus medinensis. Its larval form infects an intermediate crustacean host (Cyclops, a water flea) that commonly infests shallow ponds or step wells used as sources of human drinking water. Known to cause human suffering since ancient times, the infection was referred to by physicians as early as the Graeco-Roman era and by Arab physicians in medieval times. Common names include guinea worm and Medina worm. The worm was classified by Linnaeus in the eighteenth century. Fedchenko, a Russian naturalist, described the life cycle in 1869--the first time an invertebrate (arthropod) intermediate host was described for any parasitic disease of man.

Dracunculiasis belongs to a group of water-based diseases that includes malaria, onchocerciasis, and schistosomiasis. All of these diseases depend in some way on water as the natural habitat of an intermediate host. Unlike the others, however, dracunculiasis is transmitted only through drinking contaminated water and does not have any alternate pathways for infection. Thus, it is the only water-based disease that can be entirely prevented by protecting supplies of drinking water.

Dracunculiasis still represents a serious health risk for several millions of rural villagers in parts of Africa, the Middle East, and India. It affects only the rural poor who lack safe sources of drinking water for their households and places of work (agricultural plots). These people also often suffer from other parasites, trachoma, infant diarrheas, severe respiratory infections, and malnutrition, all of which are mayor health problems associated with poverty.

Unlike most communicable diseases in developing countries, the greatest morbidity from dracunculiasis occurs in adults. This may be the reason it has received less attention than those illnesses resulting in high morbidity and mortality in children. Because peak case rates often coincide with such agricultural activities as clearing land, planting, and harvesting, the disease is a mayor cause of agricultural work loss in many areas. Infected individuals are often crippled or disabled for many weeks each year from painful ulcers produced by the worms' emergence and complications resulting from secondary bacterial infections.

Public health authorities in endemic countries may be unaware of the annual incidence of dracunculiasis, because most patients do not attend clinics and therefore are not reported. The true burden of illness is seldom recognized, since almost no deaths occur as a result of the parasitic infection. However, reported numbers of cases and special epidemiologic studies have yielded rough estimates of the number of people at risk for acquiring dracunculiasis that range from 10-48 million throughout the world.

Etiology And Life Cycle

Guinea worms enter the human body when water containing cyclops infected with the third-stage D. medinensis larvae is swallowed. Cyclops are killed by gastric juices in the stomach, and the larvae are released. The larvae migrate quickly to the duodenal wall and proceed to the abdominal and thoracic cavities where they begin maturing in connective tissue. Male and female worms mate about 3 months after ingestion. The male worms die at 6 months of age and then become encysted, calcified, or are absorbed. The adult female worm, which measures about 70 cm long by 2 mm, lives in the connective tissues. At about 8 months female worms usually move down to the lower limbs, where the uterus containing first-stage larvae develops to fill nearly the entire adult worm.

Approximately 1 year after initial host infection, the worm is ready to emerge and to emit larvae. It migrates to the subcutaneous tissues and secretes a toxic substance that produces a painful blister. Infected people frequently try to relieve the burning sensation by immersing the affected part in water. Contact with water causes the worm's uterus to rupture and stimulates the worm to expel larvae into the water. The process is repeated intermittently over several weeks (see Figure 1).

Each female worm releases about a million microscopic first-stage larvae into the water. The larvae remain active for about 5days in pond water or step wells, where they may be ingested by cyclops exceeding a certain minimum size. When water temperature is above 21°C, the larvae inside a cyclops undergo second-stage molting and develop into the infective third stage in about 14 days. First-stage larvae swallowed directly by humans do not undergo further development and are probably killed immediately by gastric Juices. Dracunculus larvae do not reach the third stage unless they enter cyclops.

Cyclops containing third-stage larvae tend to sink to the bottom of a pond or step well, where they are more likely to be scooped up during the dry season, when water levels are low. People drawing drinking water from stagnant surface-water sources during the height of the transmission season are exposed to higher rates of infected cyclops (approximately 5 in 100 cyclops may be infected).


Figure 1: Life cycle of Dracunculus medinensis (Source: Centers for Disease Control 1981)

Although Dracunculus species are known to infect animals, the role of animal reservoir hosts in the transmission of D. medinensis to humans has not been clearly established. For example, raccoons and other wild carnivores in North America often harbor a parasite named D. insignis, which is not easily distinguished from D. medinensis. D. medinensis has also been used experimentally to infect monkeys and dogs. Even though there is no evidence to suggest that dracunculiasis is a zoonotic infection, and while the possibility of reintroduction of the parasite into unprotected human drinking water sources by possible reservoir hosts is very remote, it should not be entirely discounted.

Clinical Symptoms And Treatment

Infected people exhibit no signs or symptoms until the female worm matures and is ready to emerge. The first manifestation of dracunculiasis is localized swelling at the spot where the mature worm will emerge. In over 90 percent of cases, it emerges somewhere on the legs or feet, although worms may emerge from any part of the body. Intense burning or itching accompanies the swelling, which develops into a blister within l or 2 days. This blister ruptures several days later and becomes a superficial ulcer. Infected people often immerse the lesion in water in an effort to relieve discomfort. The worm's uterus expels larvae when the affected part is exposed to water, a process that may continue for several days to 3 weeks. Occasionally worms die before reaching the skin's surface and are absorbed, form aseptic abscesses, or become calcified, leaving cordlike masses.

Generalized nonspecific symptoms may accompany the appearance of Dracunculus at the skin, but they are usually not severe. Such symptoms may include diarrhea, vomiting, skin rashes, or asthma.

The tissues near the blister become swollen, red, and very tender, probably as part of a largely allergic reaction. There is usually a secondary infection, which commonly spreads from the initial skin lesion to deeper tissues and may be accompanied by severe or fatal septicemia. Infected ankle and knee joints can become contracted, leading to permanent crippling. Even in cases uncomplicated by secondary infection of the ulcer, the affected person may find it very difficult to walk and thus must give up his usual labors. On average, about 4-6 weeks elapse before an uncomplicated infection heals completely.

Less frequent are other severe conditions or death resulting from Dracunculus infection. These conditions include septic arthritis, tetanus, gangrene, pulmonary scarring, and ophthalmic disease.

A person may be infected by several guinea worms at the same time. Although each infection lasts a year, no effective immunity develops, and people at risk may be repeatedly infected year after year.

Because of its unusual manifestation, guinea worm disease is easily diagnosed once the worm is ready to emerge. Diagnostic tests to detect the presence of Dracunculus at earlier stages have not been developed for routine use. However, laboratory investigators have reported positive fluorescent antibody tests 6 months or more before emergence of the worm (Belcher 1981). Another nonspecific aid to diagnosis may be eosinophilia of 10-15 percent. In general, however, very little biomedical research on dracunculiasis has been carried out, thus making interpretation of findings reported in the literature quite difficult.

No drugs have proved effective in killing the adult worm prior to emergence, although some have shown experimental promise in reducing inflammation and facilitating extraction of the worm. Niridazole, metronidazole, thiabendazole, levamisole, bitoscanate, and mebendazole have been tested in humans within the last 7 years. Of these compounds, only thiabendazole is given as a short (2-day) course of treatment, which would make patient compliance more likely. One study reported that mebendazole (7-day course) resulted in significant symptomatic improvement. The action of niridazole appears to be largely one of reducing inflammation. For the most part, however, these drugs are expensive and may not be available locally. Large-scale controlled clinical trials have not been conducted, and the results of the smaller studies are difficult to interpret because of different patient selection methods, wide variation in criteria of efficacy, lack of control groups, and high drop-out rates.

The majority of infected people neither seek nor receive medical care from qualified physicians or nurses. Patients often consult healers or resort to the traditional technique of extracting the worm by rolling it a few centimeters each day around a stick or gauze (Figure 2). Infection often results if the worm breaks. Some physicians prescribe chemotherapy and make multiple incisions under local anesthesia to extract the emerging worm. Antibiotics may be given to treat secondary bacterial infections, and tetanus prophylaxis is strongly advocated.

Epidemiology

Adults between the ages of about 16 and 45 years are usually most heavily infected, although a considerable proportion of children over 5 years of age may also be affected. Young children and very old people are much less likely to acquire the disease, possibly because they do not drink as much from contaminated shallow ponds and wells near agricultural fields (Figure 3).

Because of its life cycle and the year-long incubation period, the transmission and clinical manifestations of dracunculiasis are highly seasonal. Transmission occurs only under certain climatic conditions and varies according to the local rainfall pattern. In very dry areas such as the Sahel of West Africa, transmission generally is limited to the few months during the rainy season when surface sources of drinking water become available and are used, with consequent infections becoming clinically apparent during the same period a year later. In other areas such as southern Nigeria, where rainfall is much more substantial and prolonged, the disease is most evident and is transmitted during the dry season, when surface water sources are much more scarce and contain higher concentrations of cyclops (Figure 4). Severe droughts have been known to interrupt transmission for periods sufficient to cause the disease to decline or even disappear naturally. In areas where step wells and open cisterns are used, transmission periods tend to be longer due to the persistence of cyclops in larger numbers. Because of variable transmission seasonality, local case data is important in planning control activities.


Figure 3: Age distribution of people affected by dracunculiasis (Source: Belcher et al. 1975)

Geographically, dracunculiasis occurs only in the Old World, mainly India and West Africa (Figure 5). In India the disease is limited to six states in the western part of the country; about half of the cases are reported from Rajasthan State (Figure 6). Transmission in Tamil Nadu State appears to have been interrupted recently by long-standing control measures (World Health Organization 1983). India is the only country that has actively searched for cases of dracunculiasis, and the numbers of cases reported from India are the most complete and reliable data available on the incidence of the disease (Table 1). The reported surveillance data from other countries give only an approximate indication of the most highly affected areas.

In West Africa, where probably less than 10 percent of cases are reported, the zone of highest endemicity includes Ivory Coast, Ghana, Togo, Benin, Nigeria, Mali, Niger, and Upper Volta. Questionnaire surveys are under way or have recently been conducted in Ghana, Nigeria, and Benin. Preliminary indications are that Oyo, Ondo, and Anambra may be the moat severely affected of the 16 endemic states in Nigeria, while Cross River, Rivers, and Lagos states are apparently free from the disease. According to another preliminary report, an estimated 600,000 people are affected by dracunculiasis in Benin. Niamey, Niger, appears to include the only significant urban focus of the disease (over 3,000 cases reported in 1979). Migration of infected Moshi tribesmen and women to the forest zone in Ivory Coast is thought to have spread the disease in the latter area. The most highly affected areas of Upper Volta are Banfora, Dori, Koudougou, Ouagadougou, Oushigouya, Yako, and Tenkodogo. In Ivory Coast, most cases were reported from Bouake, Boufile, Dimbokro, Tiassale, Bondoukou, and Seguela. Tsevie, Notse, and Bassari appear to be the most highly affected administrative areas in Togo.

Provision of safe water supplies by drilling wells in the rural health sector of Dimbokro, Ivory Coast, is said to have recently reduced the prevalence of dracunculiasis there from 30 percent to approximately 1 percent. A similar reduction is reported from an area of Bendel State in Nigeria. In Mali it is reported that dracunculiasis disappeared from the village of Guirel (in northern Nara) after a drought dried up the local pond for 2 consecutive years.


Figure 4: The impact of dracunculiasis on a community in southern Nigeria. Transmission is greatest during the dry season when surface water sources are scarce and contain higher concentrations of cyclops (Source: Kale 1977)

Although the disease is known to be endemic in southern Sudan, that country is the only mayor affected area where no recent surveillance information is yet available. With the probable exception of southern Sudan, the infection appears to be limited to small parts of only a few countries in East Africa and the Middle East. In Pakistan in 1969, dracunculiasis reportedly was limited to two areas involving five districts in the north-central and extreme southeast regions of the country. In 1983 Iran informed the World Health Organization that there had been no dracunculiasis in the country for the past 5 years, despite continued surveillance.


Figure 5: Areas in which dracunculiasis is reported or probably exists (Source: World Health Organization 1982)

Although the disease is easily diagnosed, and thus recognition of the problem is relatively simple, surveillance of dracunculiasis, paradoxically, is exceptionally poor. The lack of ongoing case information is due in part to the remote rural nature of affected populations, their limited attendance at government clinics, and the low government priority accorded to dracunculiasis. This situation could continue since the absence of a specific curative or preventive drug or vaccine removes a treatment incentive for villagers to visit health centers where their infection might be diagnosed and officially reported. In most endemic zones, less than 5 percent of cases are reported. Millions of cases are thought to occur annually worldwide, but systematic epidemiologic surveillance is needed to produce a reliable estimate of the annual global incidence.


Figure 6: Dracunculiasis endemicity in India (June 1982). About half of the cases are reported from Rajahstan State. (Source: World Health Report 1983)

TABLE 1 Reported Cases of Dracunculiasis in India (up to June 1982)

State

Number of Cases

Rajasthan

14,905

Karnataka

4,211

Maharashtra

3,776*

Madhya Pradesh

3,542*

Andhra Pradesh

3,049

Gujarat

423

Tamil Nadu

0

Goa

n.a.

Total

29,906

 

Social And Economic Effects

Dracunculiasis primarily affects families of subsistence farmers, with peak transmission often coinciding with heavy demands for agricultural labor. Because the worm's incubation period is approximately 1 year, farmers and their families tend to suffer the greatest number of cases during the same season each year.

Data from village studies in West Africa and India show dracunculiasis attack rates ranging from 10-40 percent or more in a single season. Some families are affected more heavily than others, with virtually all the victims incapacitated at the same time, each with one or more emerging worms. Approximately 40 percent of dracunculiasis victims are completely disabled for periods lasting 1-3 months. Villages affected by the disease experience significant losses in agricultural productivity. Families with high rates of infection may suffer during the remainder of the year from lost agricultural earnings, inadequate food supplies for home consumption, and many missed days of school. Responsibilities for working in the fields may have to be given to other members of the family, often to the detriment of adequate child care. The psychological stress of worms emerging from the leg, chest, or even genitals can also be considerable.

The adverse impact of this disease on school attendance was recently documented in Anambra State of Nigeria. In a 1979 study, Nwosu and colleagues (1982) found that the mean percentage of absenteeism attributed to dracunculiasis in 13 schools increased from an average of 13.2 + 4.6 percent to a peak of 60 percent at the height of the guinea worm season. Two schools were virtually closed for 2 weeks (Figure 7).

Unlike many other infectious diseases in developing countries that carry high mortality rates, the impact of dracunculiasis on public health is a function of length of disability, severity of illness, village attack rates, and its seasonality (Belcher et al. 1975, Kale 1977). These indicators can be related to days of work lost among the most productive age groups within the population, along with nutritional or income deficits suffered by affected families.


Figure 7: Impact of dracunculiasis on school attendance in Anambra State, Nigeria (Source: Nwosu et al. 1982) Courtesy of Liverpool School of Tropical Medicine

Control Measures

Dracunculiasis transmission is considered to be "water-based," that is, dependent on direct contact with water. The cycle of transmission requires that (1) infected individuals immerse the mature emerging worm in water used for drinking, (2) suitable cyclops species are present in that water source under optimal conditions, and (3) someone drinks water containing cyclops infected with mature Dracunculus larvae. Any break in this chain of events will interrupt transmission of dracunculiasis.

Effective personal protective or prophylactic measures that may be used include boiling the drinking water or straining 'it through a cloth to remove cyclops. The utility of these measures for a large-scale attack on the problem is somewhat diminished by their dependence on intensive educational efforts and by their inconvenience or cost (e.g., farmers quenching thirst in fields, firewood needed for boiling water). Health education, including community organization, might also be employed to encourage residents of affected villages to prevent people suffering from the disease from entering, and thereby contaminating, sources of drinking water.

Effective control measures include the periodic chemical treatment of water used for drinking in affected villages to kill cyclops. Temephos (Abate) is the insecticide most commonly used for this purpose. At concentrations of 1 part per million in stagnant surface sources of drinking water, temephos kills cyclops; is harmless to vegetation and fish; is tasteless, colorless, and odorless in drinking water; and has a wide margin of safety for ingestion by humans. Moreover, the compound has been used extensively in West Africa to control the blackfly vector of onchocerciasis.

Thus far, however, the most effective means of preventing dracunculiasis has been to provide safe water supplies. Such protected water sources prevent contamination of the drinking water by larvae from infected people, thereby breaking the chain of transmission. Provision of safe water via piped sources and protected bore and tube wells, along with the destruction or conversion of contaminated step wells, successfully eliminated dracunculiasis from large areas in the southern part of the Soviet Union in the 1920s and 1930s. In Nigeria, construction of piped water for a town of 30,000 people in the 1960s reduced the incidence of dracunculiasis from over 60 percent to zero within 2 years. In several other instances, dracunculiasis has been eliminated or drastically reduced as a side benefit of efforts to bring safe drinking water to rural populations who happen to suffer from the disease.

The current International Drinking Water Supply and Sanitation Decade offers a unique opportunity for an attack on dracunculiasis. In the context of the Decade, the provision of safe drinking water is intended for all by 1990. Hence, there is no need to justify providing safe drinking water solely as a means of eliminating dracunculiasis, only to encourage endemic countries to consider this disease when assigning relative priorities to areas where elimination of the disease would occur in addition to other benefits. Indeed, the number of villages in which dracunculiasis is endemic is estimated to be less than 10 percent of all villages targeted to receive safe drinking water during the Decade.