Bats and Rabies

  In the United States, bats are considered the major source for Rabies. Consequently, the National Institute of Health now recommends that “any person who awakens from sleep and finds a bat in the room should be urgently immunized.”

     Researchers currently believe that before the arrival of the first European colonizers, Rabies virus in the Western Hemisphere was likely present only in bats and skunks. Although native Americans were known to keep company with domestic dogs, these populations were small and spread fairly thin so ready transmission of the virus was inhibited. Modern approaches to rabies control include keeping free-roaming dog populations low. For the first 200 years of European colonization of the Americas, dog transmitted Rabies was still conspicuously absent from the historical records.     

     On the other hand, Rabies has been associated with bats in the New World since the early 16th century. Records kept by Spanish colonizers seem to indicate the presence of vampire bat-associated Rabies in the Americas. These narratives refer to people and livestock having been attacked furiously by blood-sucking bats at “twilight”, and how these encounters frequently resulted in death. 

    Rabies is an acute, highly lethal encephalomyelitis caused by viruses in the genus Lyssavirus. Current theories agree that the lyssaviruses probably originated in Old World bats, which are confirmed reservoir hosts for 14 of the 16 known viral species. Dog-maintained rabies lyssavirus (RABLV) occurs globally, but RABLV associated with bats is only found in the New World now.

    RABLV has the widest host range of all the lyssaviruses, with documented reservoir hosts occurring in a variety of species in multiple mammalian orders (Chiroptera, Carnivora, Primates). Given a clear predominance of bats as reservoir hosts of lyssaviruses, it is likely that the reservoir species of the most recent common ancestor of RABLV was an Old World bat, with the virus eventually becoming sustained in both Old World dogs and New World bats.

       In the USA, rabies in bats was first discovered in Florida in 1953. There was a subsequent boost in the number of reports in the following decade and half due to an increased interest in the problem. In the mid 1960's it was already suspected that rabies virus was likely maintained in several independent species-specific cycles in bats, highlighting the role of free tail bats (Tadarida brasiliensis), hoary bats (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans). By 1971, 25 out of the 41 extant bat species in the U. S had been found either sporadically or enzootically affected by RABLV.

   To get back to the dogs, one theory suggests that the lengthy travel times required to cross the Atlantic Ocean in the 16th century may explain why it took 200 years to start seeing dog-maintained Rabies in the Americas. If the usual incubation time for Rabies is 3-8 weeks and it takes 6 months or more to cross the Atlantic, most ill dogs will have perished by the time they reached America. As transportation improved and travel times decreased, it became more likely that infected dogs would survive the crossing, thus helping introduce dog maintained Rabies to the Western Hemisphere. Whatever the reason, it was not until the dawn of the 18th century that massive dog-maintained rabies epizootics began to occur in the WH. Domestic dogs infected both humans and terrestrial mesocarnivores such as skunks and foxes, which in turn increased the number of potential sources of human exposure. 

      The proven ability of RABLV to become established in mammals of the orders Chiroptera, Carnivora and Primates suggests that it would be possible for New World bat-associated RABLV to become re-established in the increasingly unvaccinated dog populations of the modern American mainland and the islands of the Caribbean. Re-introductions of RABLV from wildlife to dogs or from remaining pockets of dog-maintained rabies into wildlife may cascade to form new wildlife rabies reservoirs, in an endless cycle.

"The History of rabies in the Western Hemisphere."

ncbi.nlm.nih.gov/pmc/articles/PMC5620125