Figure 2: Lyssavirus transmission dynamics in bats and terrestrial animals.

Lyssaviruses seem to circulate more successfully in bats than in terrestrial mammals. A variety of factors contribute to maintenance, such as general and reservoir-specific viral factors, habitat factors and levels of human interaction. Host-specific factors, especially immune status in bats, are less understood. Although bats die upon clinical manifestation of disease, high rates of seroprevalence seen in healthy bats suggests a high frequency of abortive infection, which occurs through a combination of low exposure dosages, functional innate immune, and presence or development of neutralizing antibodies. Experimental infection studies have shown that bats can develop sub-detectable immunological memory (protection in the absence of neutralizing antibodies). However, there has never been evidence to suggest that a healthy but virus-secreting “carrier” state contributes to maintenance within bat populations. Seroprevalence in non-bats arising from natural exposure (not vaccination) are lower by comparison. Maintenance of RABV in wild and domestic carnivore reservoirs of RABV depends more heavily on variation in life history traits, population density, habitat use and degree of associations with humans. Spillover infections (in humans, for example) almost exclusively result in death before transmission to another host. The biological factors underpinning whether hosts survive or succumb to rabies, if naturally acquired VNAs are protective, and what role this has in the long-term perpetuation of RABV remain unclear.