Fasciola Gigantica: larval productivity of sheep-derived miracidia in Radix natalensis and Galba truncatula

Experimental infections of Egyptian Radix natalensis and French Galba truncatula with miracidia of Fasciola gigantica of sheep were carried out to determine the larval productivity of this parasite. Rediae and cercariae were thus counted in snails dissected at regular intervals from day 21 to day 49 post-exposure [p.e.] at 24°C, while cercarial shedding was studied in other two groups of snails after day 30 p.e. At day 49, the total number of free rediae and that of cercariae-containing rediae in R. natalensis [shell height, 10.0 mm] were 71.5 and 44, respectively, whereas mean values in G. truncatula [shell height, 5.7 mm] were 57.3 and 33 rediae, respectively. The life span of cercaria-shedding snails, the prepatent period, the patent period, and the total number of cercariae shed showed insignificant differences between both snail species. Compared to the data already obtained with a cattle isolate of parasite, the number of live rediae was significantly greater in G. truncatula and significantly lower in R. natalensis when exposed to sheep-originating miracidia. In cercariae, the differences between cattle- and sheep-derived infections were insignificant, whatever snail species. The results may be explained by the existence of an interpopulation of snail infection with F. gigantica, probably due to variations in frequency of natural encounters between this snail population and the parasite isolate. However, the better production of rediae and cercariae in G. truncatula might be due to the origin of snails used for this study because allopatric snails produced more larvae than sympatric congeners when they are subjected to experimental infections

Up-date of fasciolosis-transmitting snails in Egypt [review and comment]

Several snail species may contribute in transmission of fasciolosis in Egypt. These molluscs show a variable sensibility to natural infections with Fasciola species. Radix natalensis is considered to be the essential intermediate host for F. gigantica based on field and experimental studies. Cercarial production from R. natalensis experimentally infected with F. gigantica is affected by the species of definitive host from which the eggs are obtained, as well as the different laboratory conditions. Another lymnaeid, Galba truncatula, may play a role in transmitting this parasite in Egypt, as it was found naturally infected with F. gigantica. Latter snail species, originated from France, was susceptible to experimental infections with Egyptian miracidia of F. gigantica and it had a cercarial production close to that of local R. natalensis. Two other snails, Pseudosuccinea colurmella and Biomphalaria alexandrina, were naturally found harboring larvae of Fasciola sp. At the level of intermediate hosts of F. gigantica, the conditions are thus favorable in Egypt to transmit fasciolosis which could also be caused by another fasciolid, F. hepatica, as the existance of this fluke was confirmed in Egypt