Exposure of wild carnivores to rabies and Mokola viruses in provincial and private game reserves in Mpumalanga province

Abstract

Rabies, a disease caused by members of the genus Lyssavirus, family Rhabdoviridae is a significant veterinary and public health threat globally including South Africa. This fatal but preventable zoonotic disease causes encephalitis in all warm-blooded vertebrates including humans. At least 50 000 human fatalities and 5 million rabies exposures occur annually. However, in developing countries where both domestic (urban type) and wild (sylvatic type) rabies cycles are common and transmission occurs readily across species barriers, the disease has proven difficult to eradicate. In South Africa, the main maintenance host species include the domestic dog, Canis lupus familiaris, in Limpopo province, Mpumalanga, Eastern Cape and coastal KwaZulu/Natal provinces, and wildlife host species including the black-backed jackal, Canis mesomelas, the bat-eared fox, Otocyon megalotis, (both maintain the canid rabies biotype) and the yellow mongoose, Cynictis penicillata, that maintains the mongoose rabies biotype. There are currently 12 Lyssavirus species worldwide. In South Africa, Lagos bat virus and Duvenhage virus are rarely diagnosed in terrestrial animals and are generally associated with fruit-eating (Epomophorus wahlbergi) and insect-eating (Minopterus schreibersii) bats respectively. To date, Mokola virus (MOKV) and Ikoma virus (IKOV) are the only lyssaviruses that have not been recovered from bat species. Between 1928 and 2006, rabies was diagnosed in 4952 wildlife species in South Africa, the majority of which were mongoose species, especially Cynictis penicillata, followed by the bat eared fox, Otocyon megalotis, and the black-backed jackal, Canis mesomelas. Only one case of rabies was diagnosed in lions over the same period and no cases of Mokola virus infections have been documented in South African wildlife thus far. This project was undertaken to determine the prevalence of neutralising antibodies to RABV and MOKV, the latter a rabies-related virus, in serum samples originating from lions in private and provincial game reserves adjacent to the Mnisi communal area in Mpumalanga province and in the greater Kruger National Park. The expected benefits of the study include the evaluation of exposure of lions to RABV and MOKV in the above-mentioned region of South Africa, further improving the understanding of the epidemiology of the disease in a human/domestic animal/wildlife interface. Stored lion serum samples from the University of Pretoria, Department of Veterinary Tropical Diseases (n=140) and the Agricultural Research Council-Ondesterpoort Veterinary Institute (ARC-OVI), OIE Rabies Laboratory (n=20) and sera from other carnivores from the ARC-OVI (n=5) were tested for antibodies to classical rabies virus and Mokola virus using the fluorescent antibody virus neutralization test. All 165 sera were collected from private and provincial game reserves in Mpumalanga province between the years 1995 and 2012. The cut-off point for both RABV and MOKV serum samples was determined as 0.5 IU/ml and 0.95 IU/ml respectively. Any serum sample with a titre less than 0.5 IU/ml was regarded as negative, while any serum sample with a titre equal to or above 0.5 IU/ml was regarded as positive for RABV. Any serum sample with a titre less than an equivalent of log100.95 dilution was regarded as negative, while any serum sample with a titre equal to or above log100.95 dilution was regarded as positive for MOKV. Lion sera collected between 1995 and 2000 (n=140) had a 2.1% prevalence of RABV neutralizing antibodies and a 0.7% prevalence of MOKV antibodies. Sera collected from lions between 2010 and 2012 (n=20) had a 65.0% prevalence of RABV antibodies and a 26.3% prevalence of MOKV antibodies. Due to the uncertain vaccination status of samples collected between 2010 and 2012 and the significant differences in prevalence between the lion serum collected between 1995 and 2000 and between 2010 and 2012, the two groups of lions were treated as two separate populations. Other carnivores (n=5) had a prevalence of RABV neutralising antibodies of 40.0% and a prevalence of MOKV neutralising antibodies of 25.0%. When calculating the difference of proportions for the prevalences of the antibodies of the two lyssaviruses within each population, the prevalences were not significantly different. The results of the study suggest that lions in Kruger National Park have been exposed to RABV (2.1%) and or possibly another lyssavirus related to MOKV at low frequencies between 1995 and 2000. The sample sizes of the lions from other game reserves and other carnivores were too small to make a valid conclusion thus larger sample population sizes must be considered for future studies in these areas. Since the neutralising antibody prevalences in the Kruger National Park lions were not significantly different for both viruses, it can be concluded that if a lion presents with clinical signs of rabies, the disease is just as likely to be caused by RABV as MOKV.