Investigations on the incidence of rinderpest virus infection in game animals of N. Tanganyika and S. Kenya 1960/63

Abstract

The incidence of rinderpest infection in game animals in selected localities of South Kenya and North Tanganyika was studied during the period 1960 to 1963. Serum samples from 590 wildebeest (Connochaetes taurinus), 48 eland (Taurotragus oryx), 65 Thompson's gazelle (Gazella thompsoni) and 39 Grant's gazelle (Gazella granti) were tested for rinderpest neutralizing antibody.Rinderpest infection was shown to have been very frequent in yearling wilde-beest in the Mara area of Kenya in 1959/60, in the Serengeti National Park of Tanganyika in late 1960 and also in the Serengeti, and some adjacent areas, during the latter half of 1961. In the Ngorongoro Crater in 1961 infection was far less widespread, with only 11% of the yearlings acquiring antibody, compared to 67% in the Serengeti. The infections in 1959 and 1960 were clinical epizootics, accompanied by a considerable mortality, whereas no overt disease was reported in the course of 1961. Eland were affected in a similar manner to wildebeest up to 1960 but only a low rate of serological conversion was demonstrated in 1961. Adult Thompson's gazelle showed a low rate (ca. 12%) of infection but no anti-body was detected in Grant's gazelle.Only a small proportion of the wildebeest calves born in early 1962 acquired antibody by mid-1963 and this was due, at least in part, to infection late in 1962; it was not clear, unfortunately, whether the positive animals belonged entirely to resident, as opposed to migratory, groups. No clinical signs or mortality were reported in this year.A low incidence of rinderpest infection in wildebeest was also demonstrated both before and after 1960 in the Kajiado district of Kenya, where disease of game has not been reported in recent years. It is possible that the positive animals, as also the 1962 cases in Tanganyika, acquired the virus from low-grade infections of cattle.The transmission of rinderpest antibody from wildebeest dam to calf, presumably via the colostrum, was demonstrated regularly, except in six calves about 1–2 weeks old. No completely satisfactory explanation was obtained for their failure to acquire passive antibody but it may have been due to abnormal disturbance in the herds, associated with the shooting. The antibody titres in calves were initially higher than those in the serum of their dams but by the end of the 3rd month this position had been reversed. Individual calves became serologically negative from about the 10th week of life and all were devoid of antibody by the 6th to 7th month. The half-life of passively-acquired antibody was 4·4 weeks.