Results
Based on the ELISA PA, 21.9% (25/114) of African lions in this study tested positive for antibodies to anthrax (Table 1). Seropositivity was recorded in almost all the study areas except for the Antelope Game Park (Figure 1). A total of 5 lions (22.7%, n= 22) from high-risk zones and 20 lions (21.7%, n = 92) from low-risk zones respectively were positive for antibodies to anthrax PA antigen. However, the difference in seropositivity between the anthrax high- and low-risk zones was not significant (p= 0.852) (Table 1). Similarly, seropositivity between free-range and captive lions was not significantly different (p = 0.951) respectively at 22.6% (21/93) and 19.1% (4/21).
Figure 1. Map of Zimbabwe showing seroprevalence of anthrax in African lions sampled across the country.
With respect to lions in Hwange National Park which formed the bulk of the animals under this study, the sample distribution was biased towards the northern half of the park reflecting the spatial emphasis of the ongoing wild carnivore research projects from which the samples were drawn (Fig. 2). Seropositive lions were concentrated to the northeast part of HNP in areas which are adjacent to northern Tsholotsho (Ngamo) and Hwange Communal Lands although there were also positive lions far inland of HNP at about 90 km from the nearest park boundary.
Figure 2. Map of Hwange National Park (Zimbabwe) showing distribution of anthrax positive lions in sampled areas.
The results for comparison of serological assays for anthrax in lions, namely ELISA anti-PA antibodies and TNA are given in Table 2. There was no significant difference in the proportion of lions testing positive for anti-PA anthrax antibodies by ELISA assay and by TNA (McNemarX 2 test = 0.9, p = 0.343 at 95% significance level. The two tests had a fair agreement [Kappa (K) statistic = 0.30; 0.08<K<0.613], thus, the null hypothesis was accepted and the TNA assay validated the ELISA anti-PA antibody assay used for screening lions in this survey.