Epidemiological aspects of the interface of sylvatic and dog rabies in South Africa

Abstract

Rabies is a viral zoonotic disease that causes an estimated 60,000 preventable human fatalities in rabies affected countries every year. While very few countries have eliminated terrestrial rabies, the burden is the highest in developing countries in Africa and Asia, where 99% of human rabies cases are caused by domestic dogs. One of these rabies-endemic countries is South Africa, where canine-mediated rabies occurs throughout the country ¬–¬ causing an estimated 42 preventable human deaths every year while also impacting various livestock and sylvatic species. Although canine rabies has been described for many provinces in South Africa, the effect and possible maintenance of rabies by sylvatic species is unknown and as such, this study aimed to investigate the interface of canine and sylvatic rabies in South Africa. By using empirical rabies surveillance data collected over a 21-year period in South Africa, it was found that rabies remains endemic to canine populations throughout the country with the most cases occurring along the eastern seaboard. In contrast, our findings suggested that sylvatic rabies cases were found throughout the country, with more cases observed in rural farming communities in the northern parts of the country – specifically in the North West and Limpopo provinces. Based on this, the two provinces were selected for molecular epidemiological analyses investigating the interface between domestic and sylvatic rabies cases. The molecular epidemiological analyses relied on two gene regions (viz. the partial nucleoprotein gene and G-L intergenic region) and was used to not only update our current understanding of rabies within each province, but to identify unique rabies endemic cycles in sylvatic species. The results provided strong evidence that suggests that sylvatic species from both the North West and Limpopo provinces in South Africa were able to maintain rabies endemic cycles independently from domestic dogs. More specifically, we found evidence in support of three separate endemic cycles of sylvatic rabies throughout the North West Province and one endemic cycle of sylvatic rabies in the western parts of the Limpopo Province. In addition, we also indicated genetic homology between sequences collected from dogs and sylvatic species – suggesting that spill-over infections had occurred in both provinces. Therefore, to eliminate canine-mediated rabies from South Africa by 2030, rabies within the sylvatic populations of South Africa would need to be targeted by means of oral vaccination campaigns while canine rabies is controlled, to prevent spill-over infections from sylvatic species after canine rabies has been eliminated.