Summary
Numerous unknown factors influence anthrax epidemiology in multi-host
systems, especially at wildlife/livestock/human interfaces. Serology
tests for anti-anthrax antibodies in carnivores are useful tools in
identifying the presence or absence of Bacillus anthracis in a
range. These were employed to ascertain if the disease pattern followed
the recognized high and low risk anthrax zonation in Zimbabwe and also
to establish if anthrax was absent from Hwange National Park in which
there has been no reported outbreaks. African lions (Panthera
leo) (n= 114) drawn from -free-range protected areas and captive game
parks located in recognized high and low risk zones across Zimbabwe were
tested for antibodies to anthrax PA antigen using the ELISA immunoassay.
A random selection of 27 lion sera samples comprising 17 sero-positive
and 10 sero-negative sera (as classified by ELISA) were further tested
in the species-independent toxin neutralization assay (TNA) in order to
validate the former as a surveillance tool for anthrax in African lions.
Using the ELISA-PA immunoassay, 21.9% (25/114) of the lions tested
positive for antibodies to anthrax. Seropositivity was recorded in all
the study areas and there was no significant difference (p= 0.852) in
seropositivity between lions in high and low risk anthrax zones. Also,
there was no significant difference (McNemar’s χ2 =
0.9, p = 0.343) in the proportion of lions testing positive to the
anti-PA anthrax antibodies as tested by the ELISA-PA immunoassay and
compared to the TNA with fair agreement between the two tests [Kappa
(K) statistic = 0.30; 0.08<K<0.613]. Results of
this study indicate that anthrax could be more widespread than currently
realized in Zimbabwe, and present in recognized high and low risk zones,
including where it has not been reported in over 20 years such as Hwange
National Park. This is also the first report documenting the presence of
anthrax lethal toxin neutralizing antibodies in naturally infected
carnivores, further confirming exposure to B. anthracis . The
research results point to a need for revisiting the currently recognized
anthrax risk zones in Zimbabwe. This should be based on improved
surveillance of the disease in both wild and domestic animals for better
understanding and control of the disease.