Selection of a precocious line of the rabbit coccidium Eimeria piriformis and characterization of the life cycle of both the parent strain and the precocious line

Michal Pakandl1 and Alena Jelínková2
1Institute of Parasitology, Academy of Sciences of the Czech Republic, Branišovská 31,
370 05 Ceské Budejovice, Czech Republic
2Faculty of Biology, University of South Bohemia, Ceské Budejovice, Czech Republic
e-mail: pakandl@paru.cas.cz

The principal method used to attenuate coccidian strains is selection for early development of oocysts (precociousness). In rabbit coccidia, the precocious lines (PL) have already been obtained from five species (Eimeria coecicola, E. flavescens, E. intestinalis, E. magna and E. media), but not from E. piriformis. The aim of this work was to select PL of E. piriformis and to characterize endogenous development of both of original strain (OS) and PL. SPF rabbits were inoculated with OS oocysts and the first newly developed oocysts recovered from the intestine were used for the infection of other rabbits. The prepatent period (PP) was shortened after 12 passages from 194 to 170 hours and remained stable after 5 passages without any selection pressure. Histology and transmission electron microscopy were used to characterize the endogenous development and oocyst morphology of PL and OS. PL oocysts exhibited peculiar morphology. Besides refractile bodies (RB) within sporozoites, one huge RB merged with a residual body was present inside each sporocyst. The parasite developed in the proximal colon and in lesser extent in other parts of the large intestine. All stages were seen in the epithelium of crypts. In OS, four asexual generations preceded gamogony and, like in other rabbit coccidia, two types of meronts were observed: meronts of the type A that develop in polynucleate merozoites in which endomerogony takes place, and meronts of the type B that form uninucleate merozoites. The endogenous development of PL was identical with that of OS except the last merogony which was absent. This apparently resulted in earlier appearance of gamogony and shortening of PP. These observations of the life cycle of E. piriformis substantially correct its descriptions made 50-60 years ago, which have not been verified until recently. This work was performed in cooperation with BIOPHARM, Research Institute of Biopharmacy and Veterinary Drugs, Czech Republic.

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