Characteristics of persistent hotspots of Schistosoma mansoni in western Côte d'Ivoire.

BACKGROUND: Preventive chemotherapy with praziquantel is the cornerstone of schistosomiasis control. However, in some social-ecological settings, the prevalence and/or intensity of Schistosoma infection does not lower meaningfully despite multiple rounds of preventive chemotherapy, a phenomenon termed persistent hotspot (PHS). We assessed the characteristics of PHS in a Schistosoma mansoni-endemic area of Côte d'Ivoire. METHODS: In October 2016, a cross-sectional survey was conducted in 14 schools in the western part of Côte d'Ivoire, one year after multiple rounds of preventive chemotherapy. In each school, 50 children aged 9-12 years provided two stool samples and one urine sample. Stool samples were subjected to triplicate Kato-Katz thick smears for S. mansoni diagnosis. Urine samples were examined by a filtration method for S. haematobium eggs. PHS was defined as failure to achieve a reduction in the prevalence of S. mansoni infection of at least 35% and/or a reduction of infection intensity of at least 50%. Six schools underwent more detailed investigations, including a questionnaire survey for demographic characteristics and a malacological survey. RESULTS: In the six schools subjected to detailed investigations, the overall prevalence of S. mansoni and S. haematobium was 9.5% and 2.6%, respectively. Four schools were classified as PHS. The S. mansoni prevalence in the four PHS was 10.9% compared to 6.6% in the remaining two schools. The S. mansoni infection intensity, expressed as arithmetic mean eggs per gram of stool (EPG) among infected children, was 123.8 EPG in PHS and 18.7 EPG in the other two schools. Children bathing in open freshwater bodies were at higher odds of S. mansoni infection (odds ratio: 4.5, 95% confidence interval: 1.6-12.6). A total of 76 human-water contact sites (53 in PHS and 23 in the other schools) were examined and 688 snails were collected, including potential intermediate host snails of Schistosoma (Biomphalaria pfeifferi, Bulinus forskalii, Bu. globosus and Bu. truncatus). CONCLUSION: Children in PHS schools bathed more frequently in open freshwater bodies, and hence, they are more exposed to Schistosoma transmission. Our findings call for an integrated control approach, complementing preventive chemotherapy with other interventions, particularly in PHS settings.

Risk factors for Schistosoma mansoni and hookworm in urban farming communities in western Côte d'Ivoire.

OBJECTIVES: To identify risk factors for Schistosoma mansoni and hookworm infections in urban farming communities, and to investigate small-scale spatial patterns of infection prevalence. METHODS: A cross-sectional survey was carried out in 113 farming households (586 individuals) and 21 non-farming households (130 individuals) from six agricultural zones in the town of Man, western Côte d'Ivoire. Heads of households were interviewed on common agricultural activities, land and water use, education attainment, socioeconomic status and sanitation facilities. Household members provided stool specimens that were processed by the Kato-Katz technique and a formol-ether concentration method and diagnosed for S. mansoni, hookworms and other soil-transmitted helminths and intestinal protozoa. Bayesian statistics were employed for spatial analyses. RESULTS: The prevalences of S. mansoni and hookworm in farming households were 51.4% and 24.7%, respectively. Risk factors for a S. mansoni infection comprised living in close proximity to the Kô River, water contact with irrigation wells and ponds and low education attainment. Living in zones of smallholder irrigated rice plots or large rice perimeters, using water from domestic wells, and low socioeconomic status were risk factors for a hookworm infection. We found significant spatial heterogeneity between agricultural zones, with the highest infection prevalences of S. mansoni and hookworm in the zone where there was a large rice perimeter. CONCLUSIONS: In this urban setting, both S. mansoni and hookworm infections were related to specific agricultural activities. Health education and active participation of urban farmers for the control of schistosomiasis and soil-transmitted helminthiasis is recommended.