Supplementary studies of Pleurogenoides medians (Digenea: Lecithodendriidae) infecting the Marsh frog Rana Ridibunda (Amphibia: Ranidae) in Egypt

Pleurogenoides medians, a digenean lecithodendriid trematode, parasitize numerous aquatic vertebrate species including frogs, freshwater fish, urodeles and anurans. In the present study, a total of 190 out of 300 (63.33%) marsh frogs Rana Ridibunda were found to be infected with this digenean parasite. The highest percentage of infection was recorded in winter reaching 93.33%, and the lowest value was recorded to be 6.66% during summer. Prevalence and intensity of infection were positively correlated with the host size. Host sex showed no effect in this respect. Morphological studies based on light and scanning electron microscopy revealed that the adult worms characterized by small body size measured 1.980–2.430 (2.205 ± 0.1) mm long and 0.870–1.20 (9.87 ± 0.01) mm wide with spines of similar size distributed all over the body surface; oral sucker is sub-terminal and measured 0.180–0.230 (0.203 ± 0.01) mm long and 0.120–0.180 (0.150 ± 0.01) mm wide; ventral sucker is smaller than the oral sucker, post-ovarian located at 1/3 level from the anterior end and measured 0.080–0.102 (0.090 ± 0.001) mm long and 0.100–0140 (0.120 ± 0.001) mm wide; two symmetrical testes were located near the cecal termination on both sides of the ventral sucker, measured 0.153–0.193 (0.176 ± 0.01) mm long and 0.160–0.192 (0.175 ± 0.01) mm wide; pre-acetabular ovary was present and measured 0.130–0.150 (0.140 ± 0.01) mm long and 0.100–0.130 (0.120 ± 0.01) mm wide; vitellaria are extra-caecal and extended from the level of the pharynx to a level slightly beyond the ovary. By comparing the recovered parasite with different species of the same genus from different hosts having different localities, it was found that the present species morphometrically more or less different from the comparable species and the only similar species was P. medians described previously from the common toad Bufo bufo by having all similar characteristic features. In addition, the present study was considered as the first report for the occurrence of this lecithodendriid species infecting the marsh frog in Egypt