Fasciola hepatica : the effect of food quality on the development of redial generations in Galba truncatula infected with allopatric miracidia

Abstract

Individual bimiracidial infections of French Galba truncatula with an allopatric (Moroccan) isolate of Fasciola hepatica were carried out under laboratory conditions to count free rediae and intraredial daughter rediae in snails just after their death, and to determine whether feeding the snails on lettuce only or lettuce plus Tetraphyll had an effect on the development of redial generations. Controls consisted of snails infected with sympatric (French) miracidia and reared with lettuce only. In the allopatric group, reared with lettuce only as food, a higher mortality rate of snails in the first 4 weeks of the experiment was noted, and most G. truncatula showed 1-sporocyst infections, with the usual development of redial generations. Compared to the sympatric group, the growth of the first mother redia (R1a redia) in each snail of the allopatric group was significantly slower during the first weeks of infection, whereas a significantly increased formation of intraredial daughter rediae in the other mother rediae (R1b rediae) was noted over the same period. In the allopatric group, reared with cos lettuce and commercial fish food, 1-sporocyst infections (45.5% of snails) and 2-sporocyst infections (53.9%), with the usual development of redial generations, were noted. Compared to the sympatric group, a significantly slower development of the first mother redia during the first weeks of the experiment was noted in the 1-sporocyst infections, whereas the values in the 2-sporocyst infections did not significantly differ from those noted in the sympatric group. Similar results were noted for the production of intraredial daughter rediae in the R1b rediae during the first weeks of the experiment. In all infections derived from the growth of a single sporocyst per snail, the differentiation of numerous daughter rediae inside R1b rediae would be induced by the slow growth of the R1a redia (from which the most important group of R2a rediae originated) during the first weeks of infection and might represent a mechanism to replace free rediae absent from the inside of the snail.

Fasciola hepatica: an unusual case of adaptation to a Moroccan population of Galba truncatula

“…Regulation of redial numbers subsequently occurred, with the lysis of the remaining intraredial daughter rediae. A similar process was also noted by Belfaiza et al (2004) in French snails infected with Moroccan miracidia, which these authors explained by the quality of the diet provided to G. truncatula, as this process was not observed in infected snails raised on lettuce and commercial fish food. However, one may wonder whether such daughter redia production by all mother rediae of the first generation is not a distinctive feature of Moroccan miracidia when they infect allopatric snails.…”

“…The lengths of free rediae and the numbers of their intraredial germinal masses were only determined at days 42 and 49 p.e. Lastly, the number of intraredial daughter rediae (IDR) in the R1a, R1b, and R2a rediae was counted at day 28 p.e., as the greatest daughter redial production was noted at this date (Belfaiza et al 2004). The individual values recorded for each of these five parameters were averaged and standard deviations were calculated, taking into account the state of infection (immature, or mature) and the redial category.…”

“…The eggs of F. hepatica originated from heavily infected cattle slaughtered at the El Jadida abattoir. These were of the same origin (cattle) as those used by Belfaiza et al (2004) in their report. After their collection, the eggs were washed several times with spring water and incubated at 20°C for 20 days in the dark (Ollerenshaw 1971).…”

“…By contrast, in less susceptible snails, larval development is slow, with a few rediae mainly belonging to the first generation, and cercarial production is low (Boray 1969;Vignoles et al 2002). According to Boray (1969Boray ( , 1978, the adaptation of F. hepatica may occur rapidly as a result of several passages of the parasite in successive generations of the snail population, thus inducing a steady increase in the redial burden over time, as reported by Dreyfuss et al (2004) in the populations of Omphiscola glabra from central France since 1996.…”

Seasonal cercarial emergence patterns of Opisthorchis viverrini infecting Bithynia siamensis goniomphalos from Vientiane Province, Lao PDR

“…The feeding of snails accelerates parasite maturity so that at a given time many more mature cercariae are formed in well-fed, larger snails than smaller ones [33,34]. This is in contrast to the finding of Schmidt and Fried [29] who studied cercarial output of E. trivolvis from naturally infected H. trivolvis snails maintained under different laboratory conditions and found that food had no affect on cercarial emergence.…”