Sunday, May 31, 2009

Schistosomiasis treatment to prevent HIV?

A study published in PLoS Neglected Tropical Diseases and mentioned in the New York Times has gathered together evidence indicating that treatment for schistosomiasis, a parasitic blood trematode (worm) infection, may be a good way to prevent HIV.

The vast majority (over 90%) of the schistosomiasis disease burden is in Africa. Apart from any association with HIV, it is a damaging disease—it can lead to severe disability by causing anemia and chronic inflammation. S. haematobium, one of the three main species of the parasite infecting humans, is responsible for about 2/3 of cases in Africa and causes urinary tract infections that can lead to bladder cancer.

Now, multiple studies indicate that s. haematobium also causes Female Genital schistosomiasis (FGS). This happens when parasite eggs are deposited in a woman’s genital tract, causing lesions that look similar to an STI. They are associated with “contact bleeding” (during sex or a pelvic exam).

STI lesions facilitate HIV transmission by providing more unprotected surfaces for the virus to enter, and researchers hypothesize that FGS lesions work in exactly the same way.

It appears that only one actual study has been done so far to test this hypothesis, among rural Zimbabwean women. It found that women with FGS had a 3-fold higher risk of having HIV relative to women without FGS. However, the study was cross-sectional, making causation less clear. The authors of the Zimbabwean study called for a prospective study confirming their results.

Although no other studies have confirmed the FGS-HIV association, they have contributed to the evidence in its favor. Another Zimbabwean study, for example, reported that women who received early treatment for schistosomiasis had fewer lesions that would presumably contribute to HIV transmission.

The authors of the PLoS article, although they concede that more research must be done, also argue that the evidence we have mandates immediate implementation of treatment programs—particularly because Praziquantel, the treatment for schistosomiasis, is incredibly cheap and effective. They argue that it would be a comparatively minimal addition to PEPFAR’s budget, and could significantly prevent HIV transmission in the approximately 19 million girls at risk for developing FGS in sub-saharan Africa in the coming decade.

Older women who already have FGS lesions may not benefit very much from Praziquantel (it doesn’t usually reverse existing lesions). Therefore, The authors believe that Praziquantel should be administered early, ideally among school-age girls in areas where HIV and schisto overlap, such as Malawi, Moxambique, and Tanzania, and Zimbabwe.

Anne

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