Why Bats?
About Bats
Many of the viruses that caused recent epidemics, some with high human mortality rate, are wildlife-borne zoonoses. Among them are filoviruses (Marburg, Ebola), coronaviruses (SARS, MERS) and henipaviruses (Hendra, Nipah), which share the common feature that a dysregulated immune response contributes significantly to the damage of infected tissues and thus to the pathogenicity resulting from infection in humans. All these RNA viruses originate from bat reservoirs.
Bats were shown to have a higher mean viral richness than predicted by their phylogenetic distance from humans, their geographic range, or their presence in urban areas. This suggests that other traits must explain why bats harbor a greater number of zoonotic viruses than other mammals.
Bats are highly unusual among mammals in many other ways as well. Not only are they the only mammals capable of powered flight, but they also have extraordinarily long life spans, with little detectable increases in mortality or senescence until high ages. Their physiology likely affected their history of pathogen exposure and required adaptations that may have also affected immune signaling pathways.
Example: The SARS-CoV Experience
Pre-pandemic studies that assessed the potential emergence of SARS-like coronaviruses in (fruit) bats indicated that some of these viruses were able to use several orthologues of human ACE2 for docking and entry. These studies underscored the importance of coronavirus surveillance studies in bats, as these animals are regarded as the natural reservoir of many coronaviruses—including SARS-CoV and SARS-CoV-2.
The intranasal inoculation of fruit bats (Rousettus aegyptiacus) with SARS-CoV-2 resulted in efficient replication in the upper respiratory tract and seroconversion in seven out of nine of the bats. Transmission occurred to one out of three direct-contact animals. Clinical signs were absent, but rhinitis could be detected by immunohistology.
Conversely, previous studies showed that a SARS-like coronavirus did not replicate in fruit bats after experimental inoculation. These findings suggest that, although Rousettus bats are not the original reservoir species of SARS-CoV-2, experimental infection of these fruit bats could help to model the physiopathology of the virus in its host.
