Ultrastructure and Sporogony of Eimeria (syn. Epieimeria) anguillae (Apicomplexa) in the Eel (Anguilla anguilla)

Abstract

ABSTRACT. Ultrastructural studies on Eimeria (syn. Epieimeria) anguillae (Apicomplexa), parasite of the digestive tract of the eel, have shown that the development of this parasite takes place completely within the host cell. Merogony and gamogony are intracellular but in the epicytoplasmic position. Sporogony is also located within the epithelial cells, which agrees with assignment of this coccidian in the family Eimeriidae. However, depending on the intensity of infection and the physiopathological reaction of the host, the gamont may behave in two ways. 1) In massive infections, gamogony stages cause a genuine destruction of intestinal epithelium. Large numbers of gamonts form nodules and parts of the seriously destroyed epithelium peel off and are released into the lumen of the gut and quickly discharged into the outer environment. This discharged epithelium envelops cells containing immature oocysts that then sporulate outside the host. 2) In light infections, the host cells, which are necrotic due to the presence of a zygote, are pushed between the surrounding intact cells towards the base of the epithelium. Closely above its basal lamella, the oocyst then undergoes sporulation. These results show no taxonomically important biological features (e.g. special mode of implantation to the host cell or active movement of the zygote). Because the morphological characteristics of Epieimeria do not differ significantly from Eimeria, we propose to suppress the genus Epieimeria Dyková and Lom, 1981, and relegate its species into the genus Eimeria.