Canadian bats and their viruses: From benevolent relationships to spillover to other species

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Several viruses, that appear to cause no overt illness in their natural bat hosts, have spilled over into other mammals causing serious and often fatal disease. These include viruses that cause Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS); Marburg and Ebola haemorrhagic disease; Hendra, and Nipah respiratory and neurological disease, and porcine epidemic diarrhea (PED). While there are many studies on the interaction of these viruses with their spillover hosts or surrogate laboratory animals, there is little information on the relationship of these or similar viruses with their natural bat hosts. We therefore do not know the adaptations these viruses and their bat hosts have undergone during their co-evolution towards relatively benign relationships. There is also little information on how environmental and other factors alter the benign bat-virus relationship leading to spillover to other species. To fill these important knowledge gaps, the long-term goal of our laboratory is to define the relationship between two species of common Canadian bats and their viruses, and factors that disrupt this normally benign relationship leading to increased virus replication. Although interactions between Henipah viruses in their fruit-eating bat hosts have been studied, our work is the only known attempt to examine natural virus-host relationships in insectivorous bats. We have identified and characterized a unique coronavirus (related to SARS, MERS and PED causing viruses) and a herpes virus that naturally infect two Canadian bat species. Many, if not most bats, appear to be persistently infected with these viruses with limited virus replication and no overt signs of pathology or illness. Our preliminary studies suggest that secondary infection with a lethal fungus causes a large increase in virus load in the bats, potentially leading to spillover. Our strategy to define bat-virus relationships will be to use broad and deep information on gene expression in bats to form hypotheses on how bats respond to fungal and viral infection, test these hypotheses in cell culture models and then, in collaborative studies with bat biologists, validate the results in field samples. Our studies will not only provide fundamental information about virus-host relationships in these specialized mammals, but will also give clues about mitigating the serious consequences that often accompany viral spillover from bats to humans and other species.