Prevalence of Schistosoma japonicum infection among animals in fifty villages of Samar Province, the Philippines

In the Philippines, there is a need to understand the contribution of different domestic and wild animals in transmitting Schistosoma japonicum infection to humans better. The current study describes variation in animal S. japonicum prevalence across 50 endemic villages of Samar Province, the Philippines. A total of 50 villages were selected, 25 with predominantly rain-fed farms and 25 with some irrigation system. At least 35 cats, dogs, pigs, and water buffaloes each were randomly selected and 30 rat traps were set in each village. Fecal samples were collected for up to three consecutive days for each species. The Danish Bilharziasis Laboratory method (DBL method) was used to determine S. japonicum infection status. A hierarchical logistic regression model with clustering by village and with adjustment for measurement error of the DBL method was used to estimate the prevalence of infection per village and species. Stool samples were collected from 23.4% (1189), 28.6% (1274), 36.3% (1899), and 49.4% (873) of the censused dogs, cats, pigs, and water buffaloes, respectively, and from 663 rats. The adjusted prevalence of S. japonicum infection varied greatly across villages ranging from 1.6% (95% Bayesian Credible Interval: 0.1%-10.2%) to 86.3% (65.9%-97.8%) for dogs, from 0.1% (0%-2.1%) to 21.7% (4.7%-51.2%) for cats, from 0.01% (0.0%%-1.0%) to 18.4% (7.1%-34.7%) for pigs, from less than 0.1% (0.0%-1.2%) to 72.5% (46.0%-97.4%) for water buffaloes, and from 0.7% (0.0%-9.0%) to 95.4% (77.2%-99.9%) for rats. This is the most comprehensive study of animal S. japonicum infection conducted to date. Our results show that, unlike what has been reported in China, very few water buffaloes were infected whereas rats and dogs show high prevalence proportions of infection. This, combined with significant village-to-village variation in prevalence of S. japonicum infection, suggest possible different transmission dynamics of the infection in the Province of Samar in the Philippines and China.