The Ultrastructural Dynamics of Parasite-Host Cell Interactions as demonstrated in Besnoitia besnoiti (Apicomplexa, Protozoa):

Abstract

Besnoitia besnoiti is an obligate intracellular coccidian protozoa of significant economic importance in the regions where it occurs. The parasite exhibits two forms in its intermediate hosts; the rapidly multiplying proliferative forms (merozoites, tachyzoites) and the slowly multiplying or quiescent cyst forms (cystozoites, bradyzoites). Both forms are invasive and possess typical apicomplexan structures; a three-layered pellicle, conoid, polar ring, microtubules and rhoptries. The parasites can be maintained continuously in vitro in a variety of mammalian cell lines and their requirements for growth have been previously established. Evidence of active host cell penetration has been presented in scanning electron microscopic studies. However, such surface observations do not reveal much information on the dynamics of penetration and the manipulation of the host cell by the parasite. To understand the sequential interactions between B. besnoiti and the host cell, transmission electron microscopic examinations were carried out on infected Vero cells fixed at various time intervals following infection with Besnoitia merozoites. This article presents the ultrastructural dynamics of host cell invasion and intracellular survival of Besnoitia besnoiti. Key words: Besnoitia besnoiti, Apicomplexa, ultrastructure, Vero cells, host-cell invasion, parasitophorous vacuole.