Introduction
Anthrax, caused by the Bacillus anthracis , a spore-forming Gram-positive bacterium, is a zoonotic disease of warm-blooded animals that can be fatal for livestock, wildlife and humans (Cote, Heffron, Bozue, & Welkos, 2014; OIE, 2018; WHO, 2008). There are numerous unknown factors which influence the epidemiology of anthrax in multi-host systems, especially at wildlife/livestock/human interfaces. Anthrax induces fatal acute to peracute syndromes with no or little protective antibody immunity in herbivores. When present, protective antibody immunity often lasts less than a year in herbivores (de Vos & Turnbull, 2004; Turnbull, Doganay, Aygen, Lindeque, & Mclaughlin, 1992). However, carnivores, suids and humans are relatively resistant to anthrax with survivors or animals exposed to subclinical infections withB. anthracis mounting both cell- and antibody-mediated immunity. The duration of antibody reactivity to anthrax has been found to be much longer in surviving carnivores, and indefinite in humans (Bower et al., 2019; WHO, 2008; Turnbull et al., 1992). These attributes make carnivores ideal sentinel animals for the surveillance of anthrax in the multi-host system at the interface (Hampson et al., 2011; Mukarati et al., 2018). Indeed in Namibia, results of serological reactions toB. anthracis in wild carnivores were related to the occurrence of anthrax in herbivores in Etosha National Park, thus constituting an epidemiological tool for monitoring anthrax distribution (Turnbull et al., 1992).
Despite anthrax being considered endemic in some parts of Zimbabwe (Chikerema, Pfukenyi, Matope, & Bhebhe, 2012; Mukarati et al., 2018), the epidemiology in wildlife is poorly understood due to suboptimal surveillance and outbreak investigations. Over the past 20 years to 2018, no overt anthrax outbreaks have been reported in wildlife in Hwange National Park (HNP) despite sporadic outbreaks of the disease in livestock in adjacent communal areas of Tsholotsho District to the South-East of the park (Mukarati et al., 2018). In this study, we gathered serum from 114 wild carnivores collected across high and low risk zones in Zimbabwe in order to explore the patterns of anthrax seropositivity in lions. More specifically, after validating our ELISA-based serology results using a non-species specific toxin neutralization test, we hypothesized that low risk areas for anthrax such as HNP with no reported wildlife anthrax outbreaks for 20 years to 2018 would result in significantly low seropositivity to anthrax in wild carnivores compared to high risk areas.