|Young Women: Silence, Suspectibility and the HIV Epidemic (UNDP, 10 p.)|
The extent of the early and easy infection of young women,
exhibited in the figures above, indicates a particular susceptibility to
infection in this group. This susceptibility cannot be adequately explained by
the cultural, social or economic conditions under which young women have
intercourse, nor by the presence of infections and lesions, frequency of
intercourse or nutritional status. The possibility of physiological
vulnerability as a contributory factor must be explored
Is the intact female genital tract in young women less efficient as a barrier to virus penetration than that of older women and if so why?
A young woman's genital tract is not mature at the time she begins to menstruate. The mucous membrane changes from being a thin single layer of cells to a thick multi-layer wall. This transition is often not completed until late teens or early twenties. It is conceivable therefore that the intact but immature genital tract surface in a young women is less efficient as a barrier to HIV than the mature genital tract of older women. In post-menopausal women, the mucous membrane becomes thinner and so it is also possible that the genital tract wall, even when intact, is less efficient as a barrier.
Is mucous production in young women less proficient than in older women?
Mucus in the female genital tract has four relevant roles. It acts as a physical barrier, separating semen and other material from the vaginal and cervical walls. It is a lubricant, protecting the surface of the vagina from abrasion during intercourse. It flushes the cervix and vagina in the same way that mucus flushes the respiratory tract, removing foreign material. It has an immune function,22 that is, mucus contains cells of a separate immune system whose function is to activate the immune responses of the cells in the vaginal and cervical surfaces.
If mucous production in young women, and post-menopausal women, is less proficient than in older pre-menopausal women so too will these protective roles be less effective. There will be less of a barrier to viral penetration. It will provide less assistance in minimizing irritation and tearing of the genital membranes and so facilitate viral entry.23
It is known that the hormonal fluctuations of the menstrual cycle influence the production of vaginal and cervical secretions24. Secretion is most prolific at mid-menstrual cycle and so, at other times of the cycle of young women whose mucous secretion is not fully developed, may be inadequate. This could also be true of young women whose menstrual cycle is irregular.
Does the presence of cervical ectopy in young sexually-active women make them more prone to HIV infection?
The cervix has been postulated as the most likely site of HIV infection in women25. Any erosion of the cervix or damage to it would increase the likelihood of virus entry. An association between HIV infection and the incidence of cervical ectopy has been reported20,26 but the causal relationships need to be clarified26. In particular it urgently needs to be determined whether the presence of cervical ectopy disposes women to HIV infection. There is already considerable evidence that disproportionately more young sexually active women contract human papilloma virus and herpes simplex virus infections and that human papilloma virus infection of the cervix is a major cause of the cellular changes which lead to cervical ectopy and to cervical cancer. Furthermore, it has been known since at least 1950 that the incidence of cervical cancer is higher in young women who began sexual activity or were married before the age of 1727.
Do the hormonal and physiological changes at menopause increase the vulnerability of older women to infection?
There is some case evidence that the efficacy of transmission in post-menopausal women is higher than in pre-menopausal women28. However, epidemiological evidence is lacking since the female population most usually tested (commercial sex workers and pregnant women) do not include them. It could be anticipated that post-menopausal infected women would usually die without diagnosis or treatment.
The biology of women's genital tract is poorly understood. We know more about the increased protection from HIV infection offered by intact genital mucosae in monkeys29. The above analysis, however, does show the urgency of developing an international commitment to providing answers to these questions.