Testing and treatment programmes for HIV and schistosomiasis (also known as snail fever or bilharzia) could be profitably combined in settings with a high prevalence of both infections, results of a study published in PLOS Neglected Tropical Diseases suggest.
Retrospective research involving over 1000 HIV-serodiscordant couples in Lusaka, Zambia, showed that infection with schistosomiasis was associated with an increased risk of HIV transmission from HIV-positive to HIV-negative partners, an increased risk of HIV acquisition among women, and an increased risk of death for HIV-positive women.
The authors note that schistosome infections can be safely, effectively and cheaply treated with the anti-worm medication praziquantel. “Schistosomiasis prevention and treatment strategies may be a cost-effective way to reduce not only the symptoms associated with the infection, but also new cases of HIV and death among HIV+ persons,” they suggest.
Schistosomiasis is an infection caused by a parasitic worm that lives in fresh water. People become infected when the larvae – released by freshwater snails – penetrate the skin during contact with infested water. An estimated 200 million people have schistosomiasis worldwide and 90% of these infections are in sub-Saharan Africa.
Common types of the infection in sub-Saharan Africa are Schistosoma haematobium and Schistosoma mansoni, which cause urogenital and intestinal schistosomiasis, respectively. Most infections occur in childhood, and prevalence is generally higher in rural than urban settings.
The infection can cause a localised immune response and genital lesions. It may therefore increase the risk of HIV transmission and acquisition.
To see if this is the case, investigators designed a retrospective study involving HIV-serodiscordant couples recruited in Lusaka between 1994 and 2012.
At baseline, participants were tested for schistosome-specific antibodies (which may reflect either active or previous infection). The association between schistosome antibody status and HIV transmission, acquisition and mortality risk was then examined.
The 1046 male and 1099 female participants were followed for an average of 800 days. A fifth of men and 12% of women died during follow-up. Antiretroviral therapy was started by 10% of men and 8% of women.
The majority of participants – 59% – tested positive for schistosomiasis antibodies at baseline. This was an unexpectedly high prevalence in an urban, adult population.
Schistosomiasis antibody levels were generally higher in men than women. In HIV-positive men, the presence of schistosomiasis antibodies was associated with a higher HIV viral load (p = 0.025). In HIV-positive women, it was associated with symptoms of genital conditions (p < 0.001), genital ulcers (p < 0.001) and more advanced HIV disease (p = 0.001).
Infection with schistosomiasis as baseline significantly increased the risk of HIV transmission. In HIV-positive women, the risk of onward transmission was increased by 80% (aHR = 1.8; p = 0.002) and in HIV-positive men by 40% (aHR = 1.4; p = 0.042). A possible explanation is increased viral load and, in women, inflammatory genital lesions.
Among HIV-negative women the risk of HIV acquisition differed according to schistosomiasis type. S. haematobium, which causes genitals ulcers, significantly increased the risk (aHR = 1.4; p = 0.034), but no significant association was present for S. masoni (which affects the intestines).
Baseline schistosomiasis was significantly associated with mortality in HIV-positive women, even after controlling for confounders that included HIV viral load (aHR = 1.97; 95% CI, 1.19-3.25, p = 0.008). No such association was detected in HIV-positive men.
The researchers say their findings show the importance of schistosomiasis treatment and prevention, which should be integrated into HIV programmes. As well as reducing schistosomiasis-related illness, it could help prevent HIV transmission and mortality.
“Praziquantel treatment for schistosomiasis is safe, including in pregnant women, has no reported widespread drug resistance, has only moderate side-effects, and can be dispensed via community-wide mass administration,” they write. “Additionally, praziquantel may attenuate HIV replication by decreasing systemic inflammation and slow HIV disease progression.”
By Michael Carter
Wall KM et al. Schistosomiasis is associated with incident HIV transmission and death in Zambia. PLOS Negl Trop Dis, 12(2): e0006902, https://doi.org/10.1371/journal.pntd.0006902.