Controlling Schistosomiasis May Prevent the Spread of HIV

Strategies to prevent HIV transmission during sexual activity include consistent use of condoms and, in some cases, pre-exposure prophylaxis (PrEP). Now, a new study sheds light on another potential method of prevention: treatment for schistosomiasis.

This potentially fatal infection, caused by a parasitic worm, affects 200 million people worldwide, 90% of whom live in Africa. The parasitic worms are contracted via contaminated fresh water and travel through the skin into the body and can be excreted in urine and feces. Infection also appears to be associated with increased HIV activity.

A team of investigators at the Rollins School of Public Health at Emory University in Atlanta conducted an analysis of data from HIV-discordant heterosexual couples in Lusaka, the capital of Zambia. The couples, who had been tracked from 1994 to 2012, were part of a Zambian study designed to determine whether the level of schistosome antibodies, HIV transmission rates, and death rates were connected. The Emory team retrospectively tested blood and serum samples taken at baseline from the 2145 participants to see how many had anti-schistosome antibodies and how that related to other outcomes later on.

The Emory investigators discovered that 59% of the study participants tested positive for anti-schistosome antibodies when they first enrolled. And, the team learned, schistosomiasis created a heightened environment in which HIV can flourish.

“Our findings indicate that schistosome infection may be associated with both HIV acquisition and transmission in adults living in the Zambian capital,” Kristin M. Wall, PhD, assistant professor in the department of epidemiology at Rollins, and the study’s lead author, told Contagion®.

Digging deeper, the investigators found that there were notable gender differences when it came to study participants with and without HIV. Women who were HIV-positive and who had anti-schistosome antibodies were more likely than HIV-positive men with anti-schistosome antibodies to be at an advanced stage of HIV. Women with anti-schistosome antibodies who were HIV-negative were at increased risk of acquiring HIV, and those with anti-schistosome antibodies who were HIV-positive were more likely to progress to death than their male counterparts with the disease.

Why does this parasitic infection make HIV transmission and acquisition more likely? One possibility is a heightened viral load, according to investigators. Men with HIV may shed schistosome eggs in their semen and have more HIV-associated white blood cells in their systems. And women with HIV may have inflammatory lesions in their genitals that make it easier for the virus to be passed to partners.

One of the most significant findings of this study was the unexpected prevalence of schistosomiasis in an urban locale such as Lusaka. The disease previously had been considered a scourge affecting mainly residents living in the less populous countryside, but likely the “increased migration of individuals from rural to urban areas” has brought about a shift, said Dr. Wall.

“Though often thought of as a disease affecting rural children, our study highlights that prevention and treatment of schistosome infections may be important to reduce both schistosome morbidity as well as new cases of HIV in urban adults,” Dr. Wall explained.

Praziquantel, an anti-parasitic medication, should be made available as soon as possible for people found to have schistosomiasis, the team asserts, and routine testing for parasites should be a standard part of any evaluation for HIV.

“Praziquantel treatment for schistosomiasis is safe, including in pregnant women, has no reported widespread drug resistance, has only moderate side-effects [sic], and can be dispensed via community-wide mass administration,” they wrote in their report. “Additionally, praziquantel may attenuate HIV replication by decreasing systemic inflammation and slow HIV disease progression.”