Insufficiency of annual praziquantel treatment to control Schistosoma mansoni infections in adult women: A longitudinal cohort study in rural Tanzania.

Background Current World Health Organization (WHO) guidelines recommend annual mass drug administration using praziquantel in areas with high schistosome endemicity. Yet little is known about incidence and reinfection rates after treatment in women with frequent exposure to schistosomes. We sought to quantify response to anti-schistosome treatment and incident S. mansoni infections in a cohort of rural women living in a schistosome-endemic area of northwest Tanzania. Methods and principal findings We enrolled women with and without S. mansoni infection into a 12-month longitudinal cohort. Every 3 months, women were tested for schistosome infection using microscopic examinations for ova on filtered urine, Kato Katz slides, and serum Circulating Anodic Antigen (CAA). Those with schistosome infection received treatment with praziquantel 40 mg/kg according to the standard of care. We studied 35 women who were S. mansoni positive by stool microscopy and 46 women without schistosome infection who returned for at least one follow-up. Of the women who were initially infected, 14 (40%) were schistosome-positive at a follow-up visit. Four women developed incident infections, for a cumulative incidence of 8.7% and incidence rate of 0.99 per 100 person-months throughout the year among initially uninfected women. Only 3 women were egg-positive at any follow-up. Women with persistent, recurrent, or incident infection during the study period were significantly younger (p = 0.032) and had fewer children than women who remained uninfected or those who cleared the infection and did not experience recurrence (p = 0.003). Having fewer children remained significant after controlling for age (p = 0.023). There was no difference in initial intensity of infection by CAA or stool egg count, HIV status, or socioeconomic status. Although most water contact behaviors were comparable between the two groups, women with recurrent or incident schistosome infections were significantly more likely to have recently swum in the lake (p = 0.023). Conclusions Our data suggests that annual praziquantel treatment reduces intensity of schistosome infections but is insufficient in providing stable parasite eradication in over a third of women in endemic communities. Furthermore, microscopy lacks adequate sensitivity to evaluate efficacy of treatment in this population. Our work demonstrates that further investigation into treatment efficacy and reinfection rates is warranted and suggests that increased frequency of praziquantel treatment is needed to improve cure rates in high-risk populations. Author summary Schistosomiasis is a parasitic infection transmitted through contaminated water that primarily affects the gastrointestinal and urogenital tracts. Previous studies in Tanzania have shown that adult women infected with schistosomes also have a higher risk of contracting HIV. Although it is recommended that people living in areas where they are exposed to schistosomes be treated with praziquantel once a year, the rate of new infections or reinfection after treatment in adult women is not known. We followed a group of schistosome-infected women and an uninfected control group for 12 months. They were tested for schistosomes every 3 months, and treated with praziquantel if they were infected. Over 40% of the women tested positive for schistosome infection at some point during the follow-up period, and the majority of them were from the group that was infected at the beginning of the study. These women may not have fully cleared the infection after one treatment, or they may be more susceptible to reinfection due to variations in their immune systems. Further studies are recommended to investigate whether a higher frequency of treatment is needed to control schistosome infection in adult women, especially given that reducing schistosome infection may help to reduce HIV risk in populations similar to ours.