Infective Theileria annulata in the tick without a blood meal stimulus

Abstract

THE agent of bovine tropical theileriosis, Theileria annulata, occurs in southern Europe, North Africa and most of Asia. The disease causes high mortality and reduced yield of meat and milk in the survivors. In enzootic areas theileriosis prevents the introduction of improved stock which are in most cases very susceptible. The work described here is part of a programme for improving the effectiveness of the vaccines now used for partial control of the disease. Theileriosis is transmitted in nature mainly by adult ticks that acquire their infection in the preimaginal stages. Adults become infective after feeding for a minimum of 2 d either on the susceptible bovine host or on a non-susceptible mammal like the rabbit¹. As parasites can already be seen in the salivary glands of unfed adult ticks that are not infective^2,3, it has been assumed that a blood meal provides the biological stimulus for the development of infectivity. In attempting to determine the factors other than feeding, that might stimulate the production of infective stage(s) of T. annulata, I have found that a temperature of 37 °C and a relative humidity (RH) of 95% is in itself sufficient to stimulate the production of infective parasite forms in infected adult Hyalomma excavatum ticks without the need for a blood meal.