Genital schistosomiasis increases HIV risk for Zimbabwean women

Genital lesions caused by the waterborne parasite schistoma haemotobium increased the risk of acquiring HIV infection threefold in women living in rural Zimbabwe, according to findings from a study conducted by Norwegian and Zimbawean researchers published in the February 28^th edition of the journal AIDS.

The schistoma parasite can be acquired by bathing in water infested with the parasite, or by drinking this water. Schistosomiasis infection is predominantly a rural problem in Africa and Asia. Although the infection is known to cause genital tract lesions, no study had previously assessed whether schistosomiasis increases the risk of HIV infection in a similar way to genital lesions caused by sexually transmitted infections such as herpes.

Norwegian and Zimbabwean researchers carried out a cross-sectional study in rural north-western Zimbabwe, recruiting 527 women through a local clinic in Mupfure.

Forty-six per cent were found to have genital schistosomiasis at baseline, 29% were HIV-positive and 65% were positive for HSV-2 antibodies. HIV infection was more common in women with schistosomiasis lesions (41% vs 26%, p=0.008). Multivariate analysis showed that women with S.haematobium infection in the genitals were almost three times more likely to be HIV-positive (odds ratio 2.9, p=0.03).

Seven out of 224 women who were HIV-negative at baseline subsequently acquired HIV during one year of follow-up, an incidence of 3.1% ( six of seven had received praziquantel treatment for schistosomiasis at baseline and all had evidence of S. haematobium infection at baseline). However there was no significant difference in S. haematobium infection at baseline between the seroconverters and those who remained HIV-negative.

The authors suggest that genital schistosomiasis increases the risk of HIV infection because it causes genital lesions and `sandy patches` (areas that bleed easily) in the female genitals. S. haematobium also induces higher expression of the CCR5 receptor on the surface of T-cells, increasing the risk that those cells will become infected by HIV, and the parasite attracts immune system cells vulnerable to HIV infection into the surrounding tissue.

They say that prospective studies are needed to confirm whether genital S. haemotobium infection indeed poses a risk factor for HIV transmission, and in addition, the effect of female genital schistosomiasis as a risk factor for HIV transmission to men needs to be explored.