Development ofTrichobilharzia ocellata inLymnaea stagnalis and the effects of infection on the reproductive system of the host

Abstract

Juvenile specimens of Lymnaea stagnalis were exposed to 0 or 4 miracidia of Trichobilharzia ocellata. Highly productive infections developed in all infected snails. Qualitative and/or quantitative light microscopic observations were performed at various intervals between day 0 and 83 post exposure (p.e.). Gonadal maturation started between day 4 and 7 p.e. in all snails, but in infected animals gonadal growth was retarded considerably after day 7 and was blocked from day 19 onwards. This resulted in very small gonads (10% of the volumes of those of controls on day 83 p.e.) in infected snails, in which however, gametogenesis was initially normal. Due to the small gonad volume gamete production was highly reduced. From day 33 onwards spermatogenesis appeared to be inhibited and around day 83 oocyte maturation seemed to be impaired. The accessory sex organs (ASO) of infected snails showed a similar reduced growth. The cellular differentiation and production of secretory granules in these small ASO was normal albeit delayed in both the male and female organs. The severe reduction in growth of the gonad and the ASO started in the presence of immature primary sporocysts, the later effects on gametogenesis were simultaneous with the production of massive numbers of cercariae. These results are discussed in view of the available data on the endocrine control or reproduction in L. stagnalis. It is suggested that either the secretion of gonadotrophic hormones or the response of their targets is reduced by humoral effects of the parasites.

Changes in the reproductive biology of Biomphalara glabrata infected with different doses of Echinostoma paraensei miracidia

“…Wilson and Denison (1980), studying this same model, observed a sharp decline in the number of eggs laid by L. truncatula when infected, but at no time was there complete inhibition as reported by Hodasi. However, this divergent result could have been due to the use of different doses of miracidia, because Sluiters et al (1980) and Sluiters (1981) found a negative correlation between the number of eggs laid and the miracidial dose. Besides this, the influence of various environmental factors must be considered, such as food availability, photoperiod and population density (Sandland and Minchella, 2003;Gomot, 1990;Oliveira et al, 2008;Lustrino et al, 2010).…”

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…Global warming is predicted to have a positive effect on trematode intramolluscan stages, because their development is strongly temperature dependent, leading to increased cercarial emission rates. For example, a shorter prepatent period in relation to higher temperatures was demonstrated in experimental infections with T. szidati (141,274). A slight rise in temperature will increase developmental rates and transmission success (number of cercariae available to find the definitive host).…”

Parasitism and invasive species:effects of digenetic trematodes on mussels

“…This may lead to an increase in growth rate and/or gigantism as energy formerly allocated by the host to reproduction is put into somatic growth (e.g. Wright 1971, Wilson & Denison 1980, Sluiters 1981. However, the effect on growth rate may depend on the timing of infection.…”