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Abstract
The present study deals with studies on parasites infection in some Egyptian amphibians. The majority of individuals caught from the breeding aggregation of the two species of Anura (Rana bedriagae and Bufo regularis).
The helminth fauna consisted of one species of Nematoda, one species of Trematoda and one species of Cestoda. It was found that R. bedriagae (42%) were infected with one species of Nematoda, Falcaustra catesbeianae while B. regularis (99%) were infected with one species of Nematoda Cosmocercoides variabilis (single infection) and (63%) were infected with one species of Nematoda Cosmocercoides variabilis and one species of Cestoda Ophiotaenia magna (double infection). Moreover, only (3%) of B. regularis were infected with one species of Nematoda Cosmocercoides variabilis and one species of Trematoda Cephalogonimus americanus (double infection). These helminthes were found mainly in the small and large intestine.
In both R. bedriagae and B. regularis, their snout-vent (SV) lengths did not differ significantly between sexes and mode of parasitic infection. The composition of blood leucocytes of anuran amphibian investigated in the present study showed a parasite-specific variations. It was found that the high percentages of eosinophils were dominated in infected R. bedriagae, while low percentages were recorded in non-infected individuals. Also, low percentages of neutrophils were recorded in infected R. bedriagae. In B. regularis, high percentages of monocytes and neutrophils were dominated in non-infected toads as compared to single-or double-infected animals. Moreover, high percentages of lymphocytes and eosinophils were recorded in infected samples.
There was a significant negative correlation found between the number of parasites and ileum length in R. bedriagae. Also, a significant positive correlation was found between the number of parasites and large intestine length of frogs. In case of B. regularis there was a low positive correlation between the number of parasites and ileum and large intestine lengths.
The distribution of gut-associated lymphoid-tissues (GALT) in each region of the gastrointestinal tract of the two species variable according to the type of parasites and mode of infection. In R. bedriagae and B. regularis the gut-associated lymphoid nodules were most frequent in the ileum and also common in the duodenum and large intestine, while a few scattered nodules appeared in the stomach of non-infected and infected R. bedriagae, but appeared only in the stomach of single infected B. regularis, while the oesophagus of the two species lacked GALT. Also the number of GALT varied after parasitic infection in the two genera Rana and Bufo. GALT number was very low in stomach, increased in duodenum, reaching a maximum number in ileum and gradually decreased in large intestine.
The histopathological study showed changes in the structure of the gut in parasite-infected animals. The small intestine of the two genera Rana and Bufo infected with nematodes, showed flattened villi with proliferation of epithelial cells and metaplasia of epithelial lining of the intestinal villi to goblet cells with subepithelial leucocytic aggregations. The large intestine of the hosts infected with nematodes, showed hyperplasia of submucosa layer and there is damage in some parts of the intestinal epithelium. Also, showed metaplastic changes of epithelial lining to goblet cells. However, the small intestine of double infected B. regularis showed atrophy of the intestinal villi and the epithelial lining of mucosa was eroded down to the muscular layers with lymphocytic aggregations.
Moreover, the histological architecture of gut-associated lymphoid tissues (GALT) in parasite-infected animals showed a significant variations. In nematode-infected individuals of R. bedriagae and B. regularis numerous number of lymphoid nodules were observed in longitudinal rows or distributed evenly in the duodenum, ileum and large intestine. These lymphoid nodules in double-infected B. regularis were significantly more numerous than single-infected animals. While in non-infected animals, they were decreased in number and size. These nodules were well-vascularized with dense aggregation of lymphocytes beneath the mucosal epithelium.
In this study, it was found that the level of interleukin-2, IL-4, IL-5 and IL-2 was not significantly decreased after parasite infection in the two amphibian species studied. However, IFN-? level was significantly decreased in the both species used after parasitic infection.