Histopathological observations on the digestive gland ofLymnaea auricularia infected with larval trematodes
Histological observations were made on the digestive gland of infected and uninfected freshwater snails,Lymnaea auricularia, and the varying degree of histopathogenesis of echinostome cercaria,Cercaria itoi, as well as strigeoid metacercaria,Tetracotyle lymnaei, along withCercaria itoi (double infection) in the digestive gland have been observed. Basically 3 types of lesions, L1, L2 and L3 were found and were associated with the types and size of trematode larvae as well as with the degree of parasitemia. In the early stage of larval development or in mild infection, type I lesions (L1) were commonly observed in which degenerative changes were confined to individual digestive gland tubules, and neighbouring tubules mostly remained healthy or unaffected. The type II lesions (L2) were associated with severe infection and were less common than L1 lesions and large areas of parasitised digestive gland tubules were revealed to be necrotic. Type III lesions (L3) were also associated with severe infection in which digestive gland tubules appeared as rudimentary tubules located between trematode rediae. In the present study, in addition to a description of the different types of lesions, the various alterations of cellular structures of the digestive gland ofLymnaea auricularia due to single or double infections (Cercaria itoi + Tetracotyle lymnaei) are also discussed.