Abstract:
Theileriosis is a tick-transmitted protozoal disease caused by several Theileria species. The most virulent species affecting cattle are T. parva and T. annulata. Theileria parva is responsible for causing East Coast Fever (ECF), Corridor Disease and January Disease. Theileria parva is endemic in certain areas of South Africa, Zambia, Zimbabwe and elsewhere. In South Africa these areas are controlled, include mostly game reserves containing infected African buffaloes and are in declared Corridor disease infected districts. African buffaloes are natural reservoirs of the T. parva parasite and if suitable tick species (Rhipicephalus appendiculatus and R. zambeziensis) are present, cattle may become infected. Currently, T. parva is diagnosed by conducting an array of tests including Giemsa-stained blood and lymph node smears, indirect immunofluorescent antibody (IFA) test, standard PCR and PCR/DNA-probe test. Recent progress in the diagnosis of T. parva has involved the development of a Reverse-Line Blot (RLB) technique and a real-time PCR for detecting T. parva. Over the last decade, several outbreaks of T. parva have occurred in cattle in the province of KwaZulu- Natal. Between 2002 and 2004, Mr A. Green, a Red Brangus stud farmer in the Ladysmith district, lost a total of 42 cattle to T. parva infection. An investigation into the epidemiology of T. parva in KwaZulu-Natal was structured in three parts: (i) a survey of Red Brangus on Mr Green‟s farm in order to gain insight into the current prevalence of theileriosis and other tick-borne diseases in the herd; (ii) transmission experiments from T. parva-infected cattle on Mr Green‟s farm to susceptible cattle to demonstrate vector transmission as well as replicate the disease process and pathology; (iii) tick transmission experiments from persistently T. parva positive-testing buffalo and persistently T. parva negative-testing buffalo, to susceptible bovines to demonstrate suitability of tick transmission methods and compare pathology and clinical signs seen on the farm and in the tick transmission experiments. The survey demonstrated that several factors may interact in determining the number of infected animals, the period that they remain infective to ticks as well as the susceptibility of the rest of the herd to T. parva. Sampled bovines did not show clinical signs of T. parva-associated disease and with test results indicated that the number of subclinical carriers may be high. Attempts to transmit T. parva from infected cattle on Mr Green‟s farm to susceptible cattle were not successful. Transmission from an infected buffalo to a susceptible bovine was successful and transmission of T. parva from a negative-testing buffalo to a susceptible bovine could not be demonstrated. These experiments give some confidence that the tick-transmission methods and diagnostic tests used were reliable. It remains important to consider African buffalo as a possible source of T. parva infection in a cattle herd even when a direct link cannot be established.
