Naturally acquired antibodies to Bacillus anthracis protective antigen in vultures of southern Africa
P.C.B. TURNBULL[1], M. DIEKMANN2, J.W. KILIAN3, W. VERSFELD3, V. DE VOS4, L. ARNTZEN5, K. WOLTER6, P. BARTELS7 and A. KOTZE7,8
ABSTRACT
Sera from 19 wild caught vultures in northern Namibia and 15 (12 wild caught and 3 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 anthrax toxin protective antigen (PA). As assessed from the baseline established with a control group of 10 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. Taken as a whole, 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 Nambian group were too small to determine any significances in species-, sex- or age-related differences within the raw data showing elevated titres in 4 of 6 Cape Griffons, 6 of 10 White-backed vultures and 1 of 3 Lappet-faced vultures, or in 5 of 6 males versus 3 of 7 females, and 10 of 15 adults versus 1 of 4 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.
Keywords: Vultures, Bacillus anthracis, anthrax, antibodies, serology