Hemocyte subpopulation changes in Bithynia snails infected with Opisthorchis viverrini in Thailand.

Abstract

The Bithynia snails of B. funiculata, B. siamensis siamensis and B. siamensis goniomphalos, are first intermediate hosts of Opisthorchis viverrini. The success of parasitic infection in snails is related to the host species and efficiency of their internal defense system. Parasitic infections in snails exhibited significant variations in the number of hemocytes in hemolymph. This study investigated hemocyte counts in Bithynia snails for various durations of O. viverrini infection. The three species/subspecies snails were infected with O. viverrini and hemocytes were counted at post-exposed periods of 2, 4, 6, 12, 24, 48, 96 h, and 1, 4 and 8 wk to evaluate the hemocyte response to the infection. Three major hemocyte morphotypes, namely, agranulocytes, semigranulocytes and granulocytes, were observed. After infection, the differential hemocyte morphotype counts in all species/subspecies significantly increased in granulocytes at 2 h (p < 0.05) and decreased in semigranulocytes and agranulocytes at 2 to 4 h (p < 0.05). The total hemocyte counts were significant increased at 2 h after exposure in B. s. siamensis and B. funiculata (p < 0.05). Additionally, the number of hemocytes was reduced after exposure at 4, 6 and 12 h in B. s. goniomphalos and at 12, 24 and 48 h in B. funiculata (p < 0.05). From 96 h to 8 wk, the number of hemocytes was reestablished in the hemolymph, indicating that defensive cells in the host species have different mechanisms for their susceptibility or resistance to parasitic infections. Further studies on molecular functions will be done.