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Parasitic Worm Infection Can Increase Susceptibility to HIV, Study Finds

July 24, 2008

People infected with parasitic worms that cause schistosomiasis might be more susceptible to HIV and more likely to transmit the virus, according to a study published Tuesday in PLoS Neglected Tropical Diseases, Reuters reports. According to Reuters, the findings might help explain why HIV particularly has affected regions like sub-Saharan Africa.

Schistosomiasis -- which affects 200 million people worldwide but is seen primarily in developing countries -- is caused by flatworms that live in snail-infested freshwater such as lakes and rivers. When people wade, swim or bathe in contaminated water, the worms bore through the skin and enter the blood -- which can cause anemia, diarrhea, internal bleeding, organ damage and death -- Reuters reports.

For the study, Ruth Ruprecht of Harvard Medical School and colleagues conducted experiments on rhesus monkeys, some of which were infected with the Schistosoma mansoni parasitic worm and some that were free of the parasite and healthy. The researchers then exposed the monkeys to a hybrid virus that was genetically engineered to combine elements of HIV and simian immunodeficiency virus, or SIV. The study found that the monkeys with the parasite needed much lower amounts of the virus -- about 17 times lower -- to cause infection, compared with the parasite-free monkeys. Having the worms made the monkeys more susceptible to infection, Ruprecht said, adding that once infected, the monkeys with worms had far higher concentrations of the virus in their blood, making them more likely to transmit the virus. Study co-author Evan Secor of CDC said that the parasitic worm infection might hinder the immune system's ability to fight HIV and make it easier for HIV to enter white blood cells.

"The presence of the worm is like adding fuel to the fire -- it creates more fertile ground for the virus to take hold," Ruprecht said. Secor noted that the findings likely apply to people as well and might confirm theories that parasitic worm infections -- some of which are common in sub-Saharan Africa with unsanitary water supplies -- make people more vulnerable to HIV. "Sub-Saharan Africa has only like 10% of the world's population but almost two-thirds of the world's HIV/AIDS," Secor said. He added, "So there's an apparent disproportionate amount of HIV/AIDS there, and it's very severe. So the hypothesis is that one of the things that may contribute to the more intense nature of HIV/AIDS in sub-Saharan Africa is the presence of these parasitic worms." Ruprecht said the findings emphasize the need for public health measures to control parasitic worm infections in regions where HIV infection is common. According to Reuters, a drug called praziquantel is available to treat schistosomiasis (Dunham, Reuters, 7/22).

Online The study is available online.

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