Theileria Parva: Comparative Infection Rates of Adult and Nymphal Rhipicephalus Appendiculatus

Abstract

The tick Rhipicephalus appendiculatus is the usual vector of Theileria parva, the causative organism of East Coast fever (ECF) of cattle. When immature ticks engorge on parasitaemic cattle, they imbibe red cells containing T. parva piroplasms. The parasite subsequently undergoes a cycle of development in the body of the tick resulting in the production of a stage infective for cattle in the tick's next instar. It is generally accepted that adult ticks, which have engorged as nymphs on infected cattle, are largely responsible for the maintenance of the disease in the field (Theiler, 1905). However, Reichenow (1940) has suggested that if larval and nymphal ticks are fed on animals with the same level of infection, more parasite groups will be present in the salivary glands of the resultant nymphs than in those of the resultant adults. Reichenow also suggested that a group of nymphs, unlike a group of adult ticks, will begin to feed synchronously when applied to a host, and that the maturation of the parasite can be completed after 72 h feeding instead of 108 h as in adult female ticks.