AN OUTBREAK OF ENCEPHALOMYOCARDITIS-VIRUS INFECTION IN FREE-RANGING AFRICAN ELEPHANTS IN THE KRUGER-NATIONAL-PARK

A cluster of four deaths in late December 1993, marked the onset of an outbreak of disease of African elephants (Loxodonta africana) in the Krugel. National Park (KNP) in South Africa, which has an estimated po pulation of 7 500 elephants. Mortalities peaked in January 1994, with 32 deaths, and then declined steadily to reach pre-outbreak levels by September, but sporadic losses continued until November. During the ou tbreak altogether 64 elephants died, of which 53 (83%) were adult bull s. Archival records revealed that, in addition to the usual losses fro m known causes such as poaching and intraspecific fighting, sporadic-d eaths from unexplained causes had, in fact, occurred in widely scatter ed locations from at least 1987 onwards, and from that time until the perceived outbreak of disease there had been 48 such deaths involving 33 (69%) adult bells. Carcases had frequently become decomposed or had been scavenged by the time they were found, but seven of eight elepha nts examined early in 1994 had lesions of cardiac failure suggestive o f encephalomyocarditis (EMC)-virus infection, and the virus was isolat ed from the heart muscles of three fresh carcases. The results of test s for neutralizing antibody on 362 elephant sera collected for unrelat ed purposes from 1984 onwards and kept frozen, indicated that the viru s had been present in the KNP since at least 1987. Antibody prevalence s of 62 of 116 (53 %), 18 of 139 (13%) and seven of 33 (21%) were foun d in elephants in three different regions of the KNP in 1993 and 1994. Studies had been conducted on myomorph rodents in the KNP for unrelat ed purposes since 1984, and trapping attempts were increased during th e perceived outbreak of disease in elephants. There was a striking tem poral correlation between the occurrence of a population explosion (as evidenced by markedly increased catch rates per trap-night) and a sur ge in prevalence of antibody to EMC virus in rodents, and the occurren ce of the outbreak of disease in elephants.