Seasonal change of Lymnaeid snails intermediate host of Fasciola gigantica in North and Central Vietnam

Objective: The present study was undertaken to investigate the population dynamics of the intermediate hosts of Fasciola gigantica and the levels of infection in the snails. This would allow identifying the most important transmission periods and suggesting optimal snail control for the area.
Methods: Lymnaeid snails were monthly collected by hand picking in Ha Noi (Northern Vietnam) during the period from March 2010 to December 2011 and in Binh Dinh province (Central Vietnam) during the period May and September 2012. Collected snails from different sites were identified based on morphology and the partial 16S rDNA sequence and ITS-2 sequence. Snails were examined for the presence of Fasciola larval by the crushing method and confirmation by multiplex PCR analyses with PCR primer for Fasciola gigantica cathepsin L in parallel with the snail rDNA species specific primer.
Result: The density of Lymnaeid populations underwent great changes in relation to the geographical locations and seasons. In Central Vietnam, the Lymnaeid populations reached the peak in the dry/rainy season (May) and decreased sharply in rainy/dry season (September). In contrast, in Hanoi, it reached the peaks in 2 periods (February to April and August to November) of rice cultivation or early stage of growing of rice, and greatly deceased when the rice becomes fully developed. Transmission of fascioliasis in Ha Noi were high when rice cultivation is performed, while the permanent transmission can takes place through the year in Binh Dinh with peak transmission during the dry season.