Spatiotemporal analysis of rabies in South Africa, the role of black-backed jackals (Canis mesomelas) and aspects of its control by oral rabies vaccination

Abstract

Rabies causes fatal encephalitis in all warm-blooded animals, including humans. It is thought to have entered southern Africa in 1892 with a domestic dog (Canis lupus familiaris) from England; however, rabies was most likely present in yellow mongoose (Cynictis penicillata) before that time in southern Africa. Following the spread of disease in dogs, rabies emerged in cattle, back-backed jackal (Canis mesomelas) and side-striped jackal (Canis adustus) in Namibia, Zimbabwe and northern part of Botswana and parts of North West, Limpopo and Mpumalanga provinces of South Africa. Rabies also occurs in a variety of other wildlife hosts in South Africa. Rabies cases in all animals from 1993 to 2019 in South Africa were reviewed and analysed using a spatiotemporal cluster analysis using a discrete Poisson space-time probability model on monthly aggregated cases. Dog and livestock density were used as an estimation of the population at risk. A total of 11 701 cases were identified to species level. Thirteen primary clusters (p<0.05) were identified, of which four were long term clusters lasting more than 8 years and seven were short term clusters lasting less than 2 years. Domestic dogs accounted for 60% of all rabies cases. Wildlife was responsible for 15.8% of cases, with yellow mongoose the most frequently affected species, followed by bat-eared fox (Otocyon megalotis), black-backed jackal, meerkat (Suricata suricatta) and aardwolf (Proteles cristatus). Wildlife species affected by rabies followed different spatial distributions. Bat-eared fox and aardwolf predominated in western South Africa and yellow mongoose in central South Africa, and jackals mostly predominated in north-western South Africa, in both the Gauteng and North West provinces. To investigate the feasibility of implementing oral rabies vaccination in jackals in Gauteng province, factors associated with the uptake of oral bait by free-ranging jackal and other wildlife species were evaluated in a multi-site field study. Three different baits were offered: commercial fishmeal polymer, pieces of red meat and chicken heads. Bait uptake was observed using camera traps and patterns of uptake assessed by multiple correspondence analysis and Cox proportional hazards models. In general, all baits were well accepted with an uptake of 91% by all species, and 20% of baits were taken by jackals; median consumption time of bait for jackal was 18 hours. In species other than jackals, there was a faster uptake in the winter months when less food was available and vegetation was sparse, whereas jackal showed no seasonal preference. Chicken heads may be the preferred bait type for oral vaccination of black-backed jackal in this area, and consideration should be given to placing bait during summer and at dusk, in order to minimize uptake by non-target species such as warthogs, which are only active during the day. Two trials were conducted to assess the antibody response to oral rabies vaccine (Raboral VR-G®, Boehringer Ingelheim) in both captive and free-ranging jackals. Captive jackals (n=12) had adequate antibody titres at 4 weeks and 12 weeks and maintained sufficient antibody titres for up to 12 months (median 3.5 IU/ml; IQR: 1.5-8.25) after single oral vaccination. For testing the vaccines in free-ranging jackal habitat, four sites were baited with Raboral VR-G® vaccine: three in the northern part of South Africa and one on the central plateau, all during winter. Bait distribution, from a vehicle and on foot at these sites resulted in between 36 % and 71% of jackals tested having antibody tires to rabies after a single baiting season. Oral bait rabies vaccination could be a useful component of a control strategy for rabies in wildlife and domestic dogs in South Africa, and further work should investigate oral bait vaccine over larger areas and multiple applications.