A serological survey of Bacillus anthracis reveals widespread exposure to the pathogen in free‐range and captive lions in Zimbabwe

A massive outbreak of anthrax in the wildlife of the Malilangwe Wildlife Reserve in Zimbabwe between August and November 2004 resulted in the death of almost all the reserve's estimated 500 kudu (Tragelaphus strepsiceros). Other species badly affected were nyala (Tragelaphus angasi), bushbuck (Tragelaphus scriptus), waterbuck (Kobus ellipsiprymnus) and roan antelope (Hippotragus equinus), which suffered losses of approximately 68 per cent, 48 per cent, 44 per cent and 42 per cent of their populations, respectively. Buffalo (Syncerus caffer) were also badly affected and although their population suffered only a 6 per cent loss, the numbers of deaths ranked second highest after kudu. To the authors' knowledge, this is the first record of anthrax in wildlife in Zimbabwe.

Reports of livestock depredation by large predators were systematically collected at three study sites in northwestern Zimbabwe from 2008–2013. We recorded 1,527 incidents (2,039 animals killed and 306 injured). Lions (Panthera leo) and spotted hyaenas (Crocuta crocuta) were mostly responsible, and cattle and donkeys most frequently attacked. Patterns of predation were variable among study sites. Nevertheless, some overall patterns were apparent. Predators selected livestock close to the size of their preferred wild prey, suggesting behaviours evolved to optimise foraging success may determine the domestic species primarily preyed upon. Most attacks occurred when livestock were roaming outside and away from their ‘home’ protective enclosures at night. Hyaena attacks were largely nocturnal; lions and leopards (Panthera pardus) were more flexible, with attacks occurring by day and at night. Livestock fitted with bells suffered a disproportionate number of attacks; the sound of bells appears to have conditioned predators to associate the sound with foraging opportunities. Lion and hyaena attacks on cattle were more frequent in the wet season suggesting that seasonal herding practices may result in cattle vulnerability. Only a small proportion of conflict incidents were reported to wildlife management officials with a bias towards lion predation events, potentially prejudicing conflict management policies. Predation on domestic stock involves an intricate interplay between predator behaviour and ecology on the one hand and human behaviour and husbandry practices on the other. Our data suggest that improved livestock husbandry (supervision of grazing animals, protection at night in strong enclosures) would greatly reduce livestock depredation.

A validation of the performance characteristics of a toxin neutralization assay is presented. This in vitro assay measures the functional ability of antisera, containing antibodies to anthrax lethal toxin, to specifically protect J774A.1 cells against Bacillus anthracis lethal toxin cytotoxicity. This colormetric assay is based upon the reduction of MTT by living cells. Human and rabbit antisera produced against anthrax vaccine absorbed (AVA) were used to validate the assay. Results showed a high level of repeatability and reproducibility, particularly for a bio-assay. Inter-assay variability in absorbance values was the most prominent negative finding however, an acceptable level was demonstrated with a ratio [neutralization ratio (NR)] of the test serum 50% effective dose (ED(50)) to the reference standard ED(50). Accuracy was maintained, even in samples with minimal neutralizing capacity, and linearity was noted when sample dilutions resulted in accurate prediction of the Y(max)and Y(min). Specificity tests demonstrated that normal sera did not have an observable effect on the ability of the reference standard to neutralize toxin. The assay remained stable against time, temperature, and freeze/thaw effects on the reference standards, but not on the toxin. The assay also remained stable against media and solution storage effects. Cell passage number and cell plating density were two critical parameters identified during the robustness studies that may be responsible for inter-assay variability in absorbance values. The work was performed in accordance with the FDA's Bioanalytical Method Validation Guidance for Industry and the FDA's Good Laboratory Practice for Nonclinical Laboratory Studies (21 CFR Part 58).