Schistosomiasis

Schistosomiasis (also known as bilharzia) is a widespread parasitic infection in sub-Saharan Africa and other tropical countries that can be acquired by bathing in water infested with the parasite, or by drinking the water. Around 500 to 600 million people are at risk worldwide, in 74 countries, of whom 20 million are severely ill, another 120 million have some symptoms and another 60 million or more are infected. Its economic impact is second only to malaria.

A cross-sectional study in rural Zimbabwe¹ found that women with schistoma haematobium infection in the genitals were almost three times more likely to be HIV-positive. This is thought to be because schistosomiasis causes genital lesions and 'sandy patches' (areas that bleed easily) in the female genitals, therefore increasing the risk of HIV infection in a similar way to genital lesions caused by sexually transmitted infections.

Schistosomiasis 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.