Black-backed jackal exposure to rabies virus, canine distemper virus, and Bacillus anthracis in Etosha National Park, Namibia

Abstract

Canine distemper virus (CDV) and rabies virus (RABV) occur worldwide in wild carnivore and domestic dog populations and pose threats to wildlife conservation and public health. In Etosha National Park (ENP), Namibia, anthrax is endemic and generates carcasses frequently fed on by an unusually dense population of black-backed jackals (Canis mesomelas). Using serology, phylogenetic analyses (on samples obtained from February 2009-July 2010), and historical mortality records (1975-2011), we assessed jackal exposure to Bacillus anthracis (BA; the causal bacterial agent of anthrax), CDV, and RABV. Prevalence of antibodies against BA (95%, n = 86) and CDV (71%, n = 80) was relatively high, while that of antibodies against RABV was low (9%, n = 81). Exposure to BA increased significantly with age, and all animals >6 mo old were antibody-positive. As with BA, prevalence of antibodies against CDV increased significantly with age, with similar age-specific trends during both years of the study. No significant effect of age was found on the prevalence of antibodies against RABV. Three of the seven animals with antibodies against RABV were monitored for more than 1 yr after sampling and showed no signs of active infection. Mortality records revealed that rabid animals are destroyed nearly every year inside the ENP tourist camps. Phylogenetic analyses demonstrated that jackal RABV in ENP is part of the same transmission cycle as other dog-jackal RABV cycles in Namibia.

Figure 1

Top panel displays map of Etosha National Park, Namibia, boundaries with rectangle displaying the Okaukuejo plains where the research was conducted. Middle panel shows distribution of plains ungulate carcasses observed during opportunistic road-based surveillance over the duration of the study (January 2009 to July 2010). Bottom panel shows distribution of captured jackals. Dotted boxes show the division of the region into the Leeubron and Gemsbokvlatke study areas based on anthrax carcass distribution.

Figure 2

Endpoint titers in black-backed jackals (Canis mesomela) sampled in Etosha National Park, Namibia to the anti-protective antigen (anti-PA) Enzyme-Linked Immunosorbent Assay for exposure to Bacillus anthracis by age. Points have been jittered to facilitate display of number of samples when titers and ages are similar.

Figure 3

Seroprevalence of positivity to the canine distemper virus serum neutralization test for black-backed jackals (Canis mesomelas) by sample year and age class sampled in Etosha National Park, Namibia. Sample sizes for each category are given below each bar.