Bat rabies: Assessing risk
Recently, both state and local health departments have been inundated with telephone inquiries about the risk of rabies exposure from bat encounters, and when administration of rabies biologics would be indicated. In an effort to provide guidance regarding these issues, we offer this perspective on bat rabies in Iowa.
In the United States, over the last two decades, two to three cases of rabies from bats occurred per year, but only two of these people actually had a definite history of a bat bite. In 1998, Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices amended their recommendations concerning exposure, testing, and treatment. These recommendations now include bat encounters where no obvious bite occurred but where a very subtle bite or serious contact may have occurred.
These situations include:
- Sleeping individuals awakening to find a bat in the same room, (not just in the house)
- Young children playing alone and unobserved in a room with a bat
- Incapacitated individuals with one of these types of exposure
Testing of the bat is only required if the bat bit a human or pet, or if an exposure occurred as noted above. If the bat tests positive, indeterminate, or is unsatisfactory for testing then rabies post exposure prophylaxis (PEP) should be instituted, but would not be indicated for awake and alert persons who find a bat in a room where the person can state "the bat did not bite me."
In summary, bat exposures should be carefully evaluated for known direct exposure or probable exposure as defined above. Testing of the bat is most important when indicated for known or potential exposure. PEP is very safe and has never failed to prevent rabies if administered correctly. The best protection against exposure is provided by bat proofing one's home.
Rabies risks: Role of bat species
Over the past 50 years, human rabies in the U.S. has evolved from a pattern of dog-transmitted rabies to bat-transmitted rabies.
For the period 1990 to 2002, there have been 27 human cases of rabies from bats in the United States.
Big brown bats, a colonial species, are very common in Iowa homes and do sustain rabies activity; all 27 positive bats in 2002 were big browns.
Little brown bats, also a colonial species, but less commonly found in Iowa homes, rarely develop rabies.
The data clearly support the view that "house bats" i.e. big browns and little browns - in spite of known rabies activity, especially in big browns -- do not pose the rabies exposure risk of their chiropteran cousins, silver-hairs and eastern pipistrelles.
Accordingly, bat incidents indoors, especially in older homes with previous or known bat activity, very likely represents big/little brown species and certainly do not pose the threat of exposure risk of other species and should be considered in clinical judgments of whether to administer prophylaxis.
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