Metagenesis of intermediate host to Schistosoma japonicum Oncomelania snail in mountainous areas / 中华流行病学杂志

ABSTRACT

Objective To anderstand the metagenesis of Oncomelania snails in the mountainous regions so as to control the spread of snails and the epidemics of schistosomiasis.Methods Observation spot was established at a typical snail habitat close to Puge county,Sichuan province from February 2008 to July 2009.Random sampling was applied to determine the place of each frame during the observation.All the snails in each frame were collected and numbers counted in the laboratory,with the number of mating pairs in each frame also observed.Snails being collected were measured for the body indices and the dissection was carried out to identify gender composition.survival status and the number of live snails in each frame counted.Line graphs of the body indices.mating pairs in each observed months,bar graphs of the snail density,proportions of gender together with the maturity of the snails in each month were drawn.Results The number of live snail existed the whole year and its density fluctuated.All the three kinds of body indices showed the same time trend and a dynamic circulation.The young snail existed all year around and arose constantly in proportion from May,becoming the dominant snailin October to replace the adult snails.The young and adult snails also showed a dynamic alternative.The gender composition showed no significant difference during each month.The number of the mating pairs was more on April.May and June annually,when were the snail's main multiplying stage.Conclusion In mountain area.the young snails existed through all the year while adult snails appeared to be dominantin each month except for October.Oncomelania snail showed a circular process of metagenesis which started in May and finished in October.The snail population presented a dynamic equilibrium.It was concluded that ecological studies on Oncomelania snail were extremely relevant,either to optimally apply the existing control measures or to develop alternative measures for snail control,ecologically or biologically.