High reinfection rate after preventive chemotherapy for fishborne zoonotic trematodes in Vietnam

Abstract

Background: The World Health Organization aims for complete morbidity control of fishborne zoonotic trematodes (FZT) in endemic areas by 2020. The main intervention tool for achieving this goal is regular use of preventive chemotherapy by offering praziquantel to those at risk in endemic areas. The purpose of this study was to investigate the effectiveness of preventive chemotherapy to control FZT in an endemic area in Northern Vietnam.

Methodology and principle findings: We followed a cohort of 396 people who fulfilled the criteria for receiving preventive chemotherapy. Stool samples were examined by Kato-Katz technique for the presence of trematode eggs before, and two, 16, 29 and 60 weeks after preventive chemotherapy. The prevalence of trematode eggs in stool was 40.2% before, 2.3% two weeks after and increased to a cumulative prevalence of 29.8% sixty weeks after preventive chemotherapy.

Conclusions: The effectiveness of preventive chemotherapy as a main component in control of FZT is not well documented in most endemic areas. We found a high reinfection rate within the first year after preventive chemotherapy. Since these trematodes are zoonoses, preventive chemotherapy may not have sufficient impact alone on the transmission to have a lasting effect on the prevalence. Animal reservoirs and farm management practices must be targeted to achieve sustainable control of fishborne zoonotic trematode infections, hence control programs should consider a One Health approach.

Figure 1. Study design and cumulative absolute numbers for prevalence of fishborne zoonotic trematode eggs before preventive chemotherapy treatment and two, 16, 29 and 60 weeks after preventive chemotherapy.

*Did not receive treatment in time to be included in the study. **Did not deliver any stool samples after treatment and were excluded from further analysis. *** Missing stool samples after preventive chemotherapy were handled with imputation, i.e. a missing stool sample was regarded as negative if the previous test in the timeline was negative.

Figure 2. Prevalence of fishborne zoonotic trematode eggs in a cohort of 396 people before preventive chemotherapy, and cumulative prevalence two, 16, 29 and 60 weeks after preventive chemotherapy.

Dark grey: Both communes combined. Medium grey: Nghia Hong commune (n = 186). White: Hai Hoa commune (n = 210). Error bars are 95% confidence intervals.

Figure 3. Cumulative reinfection rate two, 16, 29 and 60 weeks after treatment (preventive chemotherapy).

The group with negative sample before treatment to the left and the group with positive sample before treatment to the right. Dark grey bars are cumulative positive samples. Light grey bars are negative samples. Missing stool samples after treatment were handled with imputation, i.e. a missing stool sample was regarded as negative if the previous test in the timeline was negative.