The ultrastructure of sporogony in Theileria cervi (Bettencourt et al., 1907) in salivary glands of female Amblyomma americanum (L.) ticks

Abstract

The process of sporogony of Theileria cervi in salivary glands of unfed and feeding Amblyomma americanum females that were infected as nymphs was studied by light and electron microscopy (SEM and TEM). Sporogony was observed only in granular acini type III and in cells classified as complex granular. Infected acini in salivary glands of both unfed and feeding ticks were enlarged. Some stages of parasite development were evident with light microscopy and SEM, but the specific events of sporogony could be documented only with TEM. Nuclear division was evident in unfed adults and continued throughout the developmental process. As the ticks fed, the parasite syncytium became increasingly complex and branches formed that were connected by thin processes. Sporozoites appeared to form by rapid sequential fission of the multinucleate sporont. Initially, sporozoites were oblong in shape and became rounded when mature. Rhoptries and micronemes were located at the hemisphere of the sporozoite that was opposite from the nucleus. Experimentally infected A. americanum transmitted T. cervi to susceptible fawns with a prepatent period of 14 and 20 days. This is the first ultrastructural description of sporogony in T. cervi in tick salivary glands.