Infection rate of Schistosoma japonicum in the snail Oncomelania hupensis quadrasi in endemic villages in the Philippines: Need for snail surveillance technique

@#Schistosomiasis japonica is one of seven NTDs endemic in the Philippines that continues to threaten public health in the country. The causative agent, the blood fluke Schistosoma japonicum, uses an amphibious snail Oncomelania hupensis quadrasi which can harbor larval stages that multiply asexually, eventually producing the infective cercariae which are shed into the water. Contamination of freshwater bodies inhabited by the snail intermediate host occurs through release of human and animal feces containing S. japonicum eggs. Miracidia hatching from these eggs subsequently infect the snails that inhabit these water bodies. The degree of fecal contamination can vary across snail sites and influences snail infection rates in these sites. In this study, conventional malacological surveys using intensive manual search for snails were conducted from 2015 to 2016 in seven selected endemic provinces, namely Leyte and Bohol in the Visayas and Surigao del Norte, Agusan del Sur, Bukidnon, Lanao del Norte and Compostela Valley in Mindanao. A total of 6,279 O. hupensis quadrasi snails were collected from 38 snail sites. The municipality of Trento in Agusan del Sur recorded the highest number of snail sites (7) that yielded O. hupensis quadrasi snails while only one snail site was found positive for O. hupensis quadrasi snails in Kapatagan in Lanao del Norte and Talibon in Bohol. Alegria in Surigao del Norte yielded the highest number of snail sites (5) that were found to harbor snails positive for S. japonicum infection. The snail infection rates in this municipality ranged from 0.43% to 14.71%. None of the snails collected from Talibon in Bohol was infected. Bohol is the only province among the 28 schistosomiasis-endemic provinces which has reached near elimination status. Snail infection rates were found to vary considerably across snail sites, which could be due to the degree of fecal contamination of the snail sites and their connectivity to water that can serve as contamination source.

Human antibody isotype responses to Schistosoma japonicum egg antigen.

Schistosoma japonicum-infected subjects from Hubei province of China were investigated to determine the class and subclass of the antibody response to soluble egg antigen (SEA), using an enzyme-linked immunosorbent assay. The subjects were 50 acute and 55 chronic cases. In acute cases, the mean OD values for IgA, IgE and IgG3 were very high, while the positive ratios of IgA and IgE were only 78% and 74%, respectively. The positive ratios of IgG, IgM, IgG1, IgG3 and IgG4 were all above 90%. In chronic cases, the mean OD values for IgG, IgG3 and IgG4 were very high, and the positivity rates of IgG, IgG1, IgG3 and IgG4 were all above 90%. Comparing the two study groups, the mean OD values of IgM, IgA, IgE were higher in acute cases than those of chronic cases (p < 0.0001), while the mean OD values of IgG, IgG4 were higher in chronic cases than in acute cases (p < 0.05). The mean OD values of IgG3 in both groups were high and those of IgG2 in both groups were low.