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  News from the Maryland Veterinary Medical Association                                                    Fall 2011

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Maryland's Bats: Fascinating and Beneficial, But Potentially Problematic
by Celeste Clements, DVM, DACVIM

Maryland is home to 10 species of bats; some are migratory and some are year-round residents. In their beneficial roles bats control insect pests and pollinate plants. Only a few species are vampires, but their villainous reputation dominates the whole order. In reality the most significant hazard that bats pose to people is their potential to transmit rabies virus, one of the world’s most significant and deadly zoonoses. Histoplasmosis is a lesser concern. Wildlife/bats/nhpbatdisease.asp

In the state of Maryland raccoons, bats, foxes, and other species of wild animals are primarily

responsible for cases of human exposure to rabies, necessitating more than 1,000 post-exposure vaccinations annually. Fortunately, our excellent public health education, wildlife control, and veterinary prophylaxis have protected Marylanders from any rabies-related fatality since 1976.

Globally, however, rabies exposure is frequently fatal, killing more than 55,000 people each year, most of whom are under 15 years of age and are bitten by dogs, often unvaccinated family pets. World Rabies Day was observed on September 28, 2011 to raise awareness about the impact of human and animal rabies, ease of prevention, and elimination strategies which were largely centered on vaccination and sterilization of dog populations in developing countries.

The State of Maryland’s One Health Bulletin regularly reports on cumulative cases of animal rabies by county. Of the 251 new cases of rabies documented through October 12, 2011 57 were isolated in bats or 23%. Raccoons were the only species to surpass this, with 131 or 52% of the cases. Domestic animals, including dogs, cats, and cattle comprised less than 7% of the total cases reported.

This summer at least 28 residents of apartment complexes in Harford County were forced to undergo rabies prophylaxis when colonies of Little Brown Bats (Myotis lucifugus) moved into their attics and crawl spaces, potentially exposing them to the virus through direct contact. Local health department officials acknowledged that the human health risk posed by this infestation was small since this bat species is not commonly infected with rabies, but since bat bites or scratches could be un-detected, especially in infants or invalids, the shots became a necessary precaution for many residents.

Unfortunately, there still is no reliable ante-mortem test for rabies in animals, and no single test that is sufficiently sensitive to exclude a diagnosis in people, so most persons opt for rabies exposure prophylaxis to prevent the predictably fatal virus. The Centers for Disease Control (CDC) website states that adverse reactions to the rabies vaccine and immune globulin are not common, and that newer vaccine products are better tolerated than vaccines previously available; thus, the prospect of rabies post-exposure treatment is less challenging than historically. When combined with vigorous washing of a wound with soap and water the results of prompt medical intervention are predictably excellent.

Members of the conservation group Bat Conservation International have partnered with the CDC, US Fish and Wildlife Service, and Department of Health and Human Services to educate the public about bats and rabies, including suggesting strategies for bat proofing a residence or outbuilding, in this brochure available online.

Excluding bats from structures during the spring, when the pups are born, or in summer by occluding their portals of entry will likely entrap immature bats that are not yet flying and result in their death by starvation.

The Department of Natural Resources for Maryland makes specific suggestions for Marylanders to attempt a peaceful coexistence with the beneficial bat. They offer recommendations for humane exclusion of bats during the fall months of September and October; guidelines for building nesting boxes as alternative housing for displaced bats; and sources for assistance with professional bat removal or exclusion.

As 2011-2012 has been designated the International Year of the Bat please take some time to read about these fascinating little flying mammals. They are happy to eat the backyard mosquitoes and will usually be happy to stay out of your hair!

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Important Links from this article

Bats and Diseases

Get Mad About Rabies

World Rabies Day

Zoonotic and Other Animal Diseases of Concern in Maryland

CDC Rabies Care Information

Bats and Rabies

Bats in Houses





© 2011 Maryland Veterinary Medical Association

PO Box 5407 • Annapolis, MD 21403 • (410) 268-1311 • fax (410) 268-1322