Dynamics and persistence of rabies in the Arctic

Abstract

Rabies is a major issue for human and animal health in the Arctic, yet little is known about its epidemiology. In particular, there is an ongoing debate regarding how Arctic rabies persists in its primary reservoir host, the Arctic fox (Vulpes lagopus), which exists in the ecosystem at very low population densities. To shed light on the mechanisms of rabies persistence in the Arctic, we built a susceptible–exposed–infectious–recovered (SEIR) epidemiological model of rabies virus transmission in an Arctic fox population interacting with red foxes (Vulpes vulpes), a rabies host that is increasingly present in the Arctic. The model suggests that rabies cannot be maintained in resource-poor areas of the Arctic, characterized by low Arctic fox density, even in the presence of continuous reintroduction of the virus by infected Arctic foxes from neighbouring regions. However, in populations of relatively high Arctic fox density, rabies persists under conditions of higher transmission rate, prolonged infectious period and for a broad range of incubation periods. Introducing the strong cyclical dynamics of Arctic prey availability makes simulated rabies outbreaks less regular but more intense, with an onset that does not neatly track peaks in Arctic fox density. Finally, interaction between Arctic and red foxes increases the frequency and/or the intensity of rabies outbreaks in the Arctic fox population. Our work suggests that disruption of prey cycles and increasing interactions between Arctic and red foxes due to climate change and northern development may significantly change the epidemiology of rabies across the Arctic.

Relationships between fox populations and rabies virus spread in northern Canada

“…The genetic diversity of the Arctic lineage of rabies virus described here clearly supports a model in which the virus is continuously evolving through mostly neutral mutation and purifying selection to spawn distinct genetic groups. Modelling studies of Arctic rabies have suggested that a variety of factors including high transmission rates, relatively short incubation periods but long infectious periods and ongoing immigration of infectious conspecifics from other areas could help in maintaining rabies outbreaks in northern Canada; however, various scenarios in which outbreak die-offs occurred were also often predicted [ 60 ]. Indeed, the rabies virus phylogeny illustrated here does suggest that while some viral groups appear to circulate only very locally and die off relatively quickly (e.g.…”

Understanding rabies persistence in low-density fox populations

“…Parameter values provided in Table 1 are based on Anderson et al (1981) and Simon et al (2019), and parameter values were also cross-referenced with Mørk and Prestrud (2004) to ensure biological relevance for arctic fox populations. The parameter set, derived from demographic studies of foxes, yields a theoretically simulated disease density threshold of 1 fox/km 2 .…”

“…However, those commonly used models can predict densities not found in nature. For instance, Anderson et al (1981) predicts rabies persistence in Europe when densities of its regional host, red fox (Vulpes vulpes), are as low as 1 fox/km 2 , yet rabies persists in the tundra when densities of arctic fox (Vulpes lagopus) are well below this threshold (Simon et al 2019). One way such a contradiction could exist is that environmental heterogeneity may lower threshold host densities for disease persistence.…”

“…Contrary to the well-documented disease density threshold (K T ) of approximately 1 fox/km 2 (Anderson et al 1981), arctic rabies persists endemically at densities below this. Indeed, landscape-level arctic fox densities rarely exceed 0.3 breeders/km 2 (Angerbjörn et al 1999;Eide et al 2004;Simon et al 2019). When these numbers are scaled into total number of foxes per square kilometer, by including non-breeding foxes and juvenile survival, Arctic densities are still unlikely to exceed an average of 1 fox/km 2 .…”

“…Still, many critical questions, such as the spread and maintenance of rabies in the Arctic, are largely unresolved (Mørk and Prestrud 2004). Simon et al (2019) extended Anderson et al (1981) to consider high transmission rates, short incubation periods, prolonged infectious periods, periodicity in the birth rate, and interaction with red foxes. With these modifications to Anderson's model, rabies can persist in the Arctic with fox densities lower than 0.15 fox/km 2 , yet at low densities, immigration will cause sporadic outbreaks of rabies, and this leaves open the question of dispersal's role in arctic rabies endemicity (Simon et al 2019).…”