Abstract
Sera from 19 wild caught vultures in northern Namibia and 15 (12 wild caught and three captive bred but with minimal histories) in North West Province, South Africa, were examined by an enzyme-linked immunosorbent assay (ELISA) for antibodies to the Bacillus anthracis toxin protective antigen (PA). As assessed from the baseline established with a control group of ten captive reared vultures with well-documented histories, elevated titres were found in 12 of the 19 (63%) wild caught Namibian birds as compared with none of the 15 South African ones. There was a highly significant difference between the Namibian group as a whole and the other groups (P < 0.001) and no significant difference between the South African and control groups (P > 0.05). Numbers in the Namibian group were too small to determine any significances in species-, sex- or age-related differences within the raw data showing elevated titres in four out of six Cape Vultures, Gyps coprotheres, six out of ten White-backed Vultures, Gyps africanus, and one out of three Lappet-faced Vultures, Aegypius tracheliotus, or in five of six males versus three of seven females, and ten of 15 adults versus one of four juveniles. The results are in line with the available data on the incidence of anthrax in northern Namibia and South Africa and the likely contact of the vultures tested with anthrax carcasses. It is not known whether elevated titre indicates infection per se in vultures or absorption of incompletely digested epitopes of the toxin or both. The results are discussed in relation to distances travelled by vultures as determined by new tracking techniques, how serology can reveal anthrax activity in an area and the issue of the role of vultures in transmission of anthrax.
Highlights
It has been a long-held suspicion that vultures transmit anthrax over long distances (Bullock 1956; Ebedes 1976)
Biologist at the Kruger National Park (KNP) in the 1960s, held the conviction that water polluted by vultures bathing in their hundreds rendered waterhole water an important source of anthrax in the KNP (Pienaar 1961, 1967) and V. de Vos, long-time veterinarian and scientific adviser in the KNP, has continued to support the theory that vultures contribute to the transmission of anthrax by contaminating water holes
They felt too little was known about diseases of vultures to be able to assess (a). While they considered that (b) can undoubtedly occur, they felt the most important potential method of disease dissemination would come from (c) and (d). They fed anthrax vaccine spores to White-backed Vultures and recovered them from the faeces but failed to recover what they implied were vegetative Bacillus anthracis cells
Summary
It has been a long-held suspicion that vultures transmit anthrax over long distances (Bullock 1956; Ebedes 1976). Houston & Cooper (1975) considered that for a vulture to play a role in disease transmission, the agent of the disease must (a) cause clinical or subclinical infection and be passed out in the bird’s secretions or excretions, or be spread by vectors, or (b) be transmitted mechanically on the bird’s feet or feathers, or (c) be regurgitated with pellets from the crop, or (d) pass through the vulture’s alimentary tract and be voided in the faeces They felt too little was known about diseases of vultures to be able to assess (a). They fed anthrax vaccine spores to White-backed Vultures and recovered them from the faeces but failed to recover what they implied were vegetative Bacillus anthracis cells ( the culture details are not given and feeding the spore form of B. anthracis alone, is not truly representative of what occurs in the field). Lindeque & Turnbull (1994) found that anthrax spores could be detected at low concentrations in the faeces of vultures associated with anthrax carcasses
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