New endemic foci of schistosomiasis infections in the Philippines

Abstract

Schistosomiasis affects 28 provinces in the Philippines found along the southeastern part where there is continuous rainfall throughout the year. In 2002 and 2005 respectively, two new endemic foci were reported in the northernmost (Gonzaga, Cagayan) and central (Calatrava, Negros Occidental) parts of the country. This study conducted in March 2008-March 2009 confirmed the presence of the disease by determining its prevalence using four diagnostic tests - Kato-Katz, circumoval precipitin test (COPT), ELISA and ultrasonography. Oncomelania hupensis quadrasi was identified through snail surveys conducted in possible snail habitats in the seven new endemic villages. Animal surveys through stool examination confirmed the presence of schistosomiasis infection in animals in Gonzaga but not in Calatrava. Compared to Calatrava, Gonzaga demonstrated markedly higher prevalence of schistosomiasis using all four diagnostic methods. Proximity of snail habitats to human habitation including higher snail density and snail infection rate could be responsible for the high prevalence. Snail sites were more widespread in Gonzaga whereas those in Calatrava were confined only in areas not frequented by the general population except by farmers. GIS maps showing spatial distribution of snails in Gonzaga and Calatrava indicated differences in elevation among the snail sites. It is hypothesized that the snail intermediate host has been in these sites for sometime but discovered only lately. Migration of people from endemic provinces into Gonzaga and Calatrava brought in cases and in the presence of snail intermediate hosts, emergence of disease was just a matter of time.

Keywords: Calatrava; Gonzaga; New endemic foci; Oncomelania quadrasi; Schistosomiasis.