Histological and histochemical observations on the digestive gland ofMelanoides tuberculatus (Gastropoda) infected with certain larval trematodes and focus on their mode of nutrition

Abstract

Histological and histochemical observations were made on infected and uninfected digestive glands of snails, Melanoides tuberculatus. Infected gland either with sporocysts of Cercaria diqlandulata (Xiphidio) or with rediae of Cercaria martini (Monostome) revealed basically two types of histopathological abnormalities (damages), mechanical (lesion 1) and physiological (lesion 2). Depletion of carbohydrates, lipids and proteins as well as increased activities of phosphatases, lipase, non-specific esterase and glucose-6-phosphatase were also reflected by infected digestive gland. Alterations either histological or histochemical in infected glands are associated with the type and size of trematode larvae and degree of parasitemea and these were greater in glands infected with rediae than in sporocysts, Besides pathogenesis, the present study also focusses on the mode of nutrition in certain trematode larvae.

Histopathological effects of larval trematodes on the digestive gland of freshwater snail species, Vivipara bengalensis and Lymnaea acuminata

“…The physiological changes as autolysis and/or necrosis are possibly the result of the release of proteolytic enzymes from the ruptured digestive cells/or enzymatic secretion and metabolites from trematode larvae. This lends support from previous reports of certain snail species (Choubisa 1988(Choubisa , 2008b. Starvation autolysis was due to squeezing of digestive tubules at different loci and consequently no food was able to pass into the tubules.…”

“…Therefore, there is a possibility of intracellular digestion. Hence, atrophy of digestive tubules was generally found in heavy infection, especially in double infection as has been observed in earlier studies (Mohandas 1974;Choubisa 1988). Another possible reason for reduction in size of epithelial cells and increasing of inter and intra-tubular spaces of glands is reduction in the amount of stored nutrients and energy due to increasing demands of the developing host gonads as well as developing or multiplying parthenitae (Bertman 1980).…”

“…The next day, larval digeneans were recovered from infected snails and identified as earlier reported (Choubisa 2008a). The infected and uninfected digestive gland (hepatopancreas) of these snail species were processed for histology as described in previous reports (Choubisa 1988). The stained sections were observed using Olympus Ch20i TR microscope equipped with Olympus E 450 digital camera.…”

“…Another possible reason for reduction in size of epithelial cells and increasing of inter and intra-tubular spaces of glands is reduction in the amount of stored nutrients and energy due to increasing demands of the developing host gonads as well as developing or multiplying parthenitae (Bertman 1980). It has been discussed in earlier studies (Mohandas 1977;Choubisa 1988) that redial stages cause more mechanical and physiological damage as compared to sporocysts because of their mouth and locomotory organs while their pharyngeal glands and gut contribute for the physiological damages. It has also been observed that rediae engulf the host's digestive cells and utilize the hydrolases (Choubisa 1988(Choubisa , 2008b for their extra cellular digestion.…”

“…It has been discussed in earlier studies (Mohandas 1977;Choubisa 1988) that redial stages cause more mechanical and physiological damage as compared to sporocysts because of their mouth and locomotory organs while their pharyngeal glands and gut contribute for the physiological damages. It has also been observed that rediae engulf the host's digestive cells and utilize the hydrolases (Choubisa 1988(Choubisa , 2008b for their extra cellular digestion. Thus it can be conjectured that redial stages are more destructive for the host tissues in the present cases.…”