Variation in Susceptibility to Tsetse-Borne Trypanosomiasis Among Three Bos indicus Cattle Breeds in Different Tsetse Endemic Localities in Kenya

Tsetse-transmitted Afican bovine trypanosomiasis is a major disease limiting livestock production in large areas of Africa. The current methods of disease control are aimed at vector (tsetse) control or the use of drugs to treat or prevention of infection. Tsetse control operations are expensive to implement and maintain, while there are few drugs currently available. In addition, the parasites frequently develop resistance to the drugs following prolonged use. Currently the utilization of cattle breeds that possess a degree of resistance to the disease has been viewed as an additional tool for the control of trypanosomiasis. This approach has been studied extensively in West African cattle but there has been little attention in East African livestock. This thesis was therefore designed to investigate the variation in susceptibility among three breeds of Bos indicus cattle breeds, the Maasai Zebu, Orma Boran and Galana Boran kept under varying levels of tsetse challenge in different parts of Kenya. The first chapter reviews the disease epidemiology and current control methods with emphasis on genetic resistance. Chapter 2 summarizes the previous epidemiological work on breed variation carried out at the Kenya Trypanosomiasis Research Institute (KETRI) which led to this investigation. In Chapter 3, the study areas are described together with the livestock production systems and the constraints to production. In addition, a brief review of the history of Bos indicus cattle in East Africa with emphasis on the breeds studied and the epidemiological data collected is given. The field experiments are reported in Chapter 4. Section 4.1 presents the work carried out between September 1989 and September 1990 in high and low tsetse challenge areas at the Nguruman escarpment. South Western Kenya, involving Maasai Zebu cattle from Nguruman, Orma Boran and Galana Boran cattle transferred from the Galana Ranch on the Kenya coast. In the high challenge area, it was observed that, both the Maasai Zebu and Orma Boran were less susceptible to trypanosome infections as judged by the disease incidence, degree of anaemia, drug requirements and the body weight gains. In the low challenge area, where the tsetse fly population was controlled using odour-baited traps, only the Maasai Zebu and Orma Boran were compared. The results indicated that, there were no significant differences in the disease incidence, degree of anaemia and the growth rates between the two breeds. The cattle that survived from the high tsetse challenge area at Nguruman were transferred to the Galana Ranch, where they were compared with new groups of Maasai Zebu and Orma and Galana Boran with no previous exposure, for a period of nine months from May 1991 to February 1992. The Maasai Zebu cattle were purchased from farmers at the Nguruman escarpment and transferred to the Galana Ranch, while the Orma and Galana Boran cattle were purchased locally at the Galana Ranch. The results, presented in section 4.2, showed no significant differences in susceptibility among the cattle with previous exposure. On the other hand, among the cattle with no previous exposure, the Maasai Zebu and Orma Boran were significantly less susceptible to trypanosomiasis than the Galana Boran as indicated by the disease incidence, degree of anaemia, drug treatments and the growth rates. This study has therefore indicated that the Maasai Zebu and Orma Boran possess a superior resistance to trypanosomiasis than the Galana Boran and that, the resistance is not restricted to one locality. They also suggest that previous exposure does influence the susceptibility. The last aspect of this study (Chapter 5) involved the comparison of the parasitological (darkground/phase contrast buffy coat technique and mouse inoculation) and immunological techniques (antigen and antibody enzyme-linked immunoassays) for the diagnosis of trypanosome infections in cattle exposed to natural tsetse challenge. It was observed that for complete epidemiological information, a combination of more than one technique preferably the darkground phase/buffy coat contrast and the antigen ELISA would be ideal. Chapter 6 presents the general discussion, conclusions and recommendations.