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.