Differential development and emission ofTheileria parvasporozoites from the salivary gland ofRhipicephalus appendiculatus

Abstract

SUMMARYThe initiation of feeding of infectedRhipicephalus appendiculatusadults induces the rapid development ofTheileria parvasporoblasts within the salivary gland acini leading to the production of numerous sporozoites which are inoculated into the mammalian host initiating infection. In this study the pattern of development, host cell specificity and emission ofT. parvasporozoites within the salivary glands of heavily infected, 4-day fed adultR. appendiculatusticks was examined. Infected acini were randomly distributed throughout the salivary gland. Sporozoite development within each gland was not synchronized and wide variation in the rate of parasite development, which correlated with the secretory activity of the individual acinus, was observed in all glands examined. Previous studies had shown thatT. parvadeveloped primarily in Type III ‘e’ cells. However, in heavily infected salivary glands sporogony and the emission of mature sporozoites also occurred in ‘c’ cells of Type II acini. Sporozoite emission from infected cells occurred by a process similar to apocrine secretion. The loss of the apical membrane of the infected cell allowed sporozoites free access to the lumen of the acinus and into the collecting ducts of the salivary gland. Sporozoite discharge was gradual since few parasites were found in the acinus valve or in the collecting ducts. Furthermore, the small size of the acinar valve aperature ensures that only small numbers of sporozoites can be released at any one time from an infected acinus.