Bats and Diseases

​​The majority of bats that people encounter are healthy, but bats can get sick just like humans and other animals. Some of the diseases that infect bats may also be transmitted to people. Rabies and histoplasmosis are the most important public health issues to consider when dealing with bats.

White Nose Syndrome

Carcass of Little Brown Bat found on floor of Maryland CaveWhite-nose syndrome (WNS) was first documented in Maryland during a department survey of a bat hibernation site in an Allegany County cave near Cumberland on March 5, 2010. Several dead bats and over two hundred visibly affected bats were found during the survey. The white fungus, often concentrated around the muzzle, is white-nose syndrome, a disease which has killed more than 5.7 million bats in the eastern United States. In Maryland, Heritage ecologist Dan Feller has documented as much as 90-100% loss of bats in infected hibernacula.

Bats with WNS use up their fat reserves before winter ends, likely the result of increased frequency of arousal during hibernation. Starving bats may fly outside the cave and die because their main food source, insects, are not active in cold weather.

Little Brown Bats showing fungal growth on their muzzles White-nose syndrome was first discovered in a cave near Albany, New York in February 2006. Since then, WNS has been confirmed in over 30 states in the eastern U.S. and in 7 Canadian provinces. Since 2006, biologists have reported as much as a 100% decline in hibernating bats in affected caves. Recent research indicates that the fungus, Geomyces destructans, associated with WNS is a non-native pathogen recently introduced to the United States from Europe. WNS has caused unprecedented declines of bats and the ecological consequences are unknown.

Though not known to be harmful to humans, there is an urgent need to prevent the spr​ead of this deadly syndrome. WNS is likely spread by contact among bats and with their environment. Scientists have evidence that WNS could be transferred to caves from humans visiting caves. Contaminated clothing and gear may transmit spores into new areas; potentially impacting additional vital bats populations. For information on what you can do to help bats, please check out the page here:

The USFWS requests that cavers refrain from caving in all WNS affected states and adjoining states. Cavers should refrain from caving anywhere during hibernation (September-May) to minimize disturbance and mortality to bats. Decontamination protocol can be found here:

For up to date information on WNS, please visit the U.S. Fish and Wildlife Service website at:

Following US Fish and Wildlife Service recommendations, Maryland cave access should be closed to all human activity except for approved research.

White-nose Syndrome Factsheet


Battle For Bats: Surviving White Nose Syndrome from Ravenswood Media on Vimeo.

Battle For Bats: Surviving White Nose Syndrome was produced for the USDA Forest Service by Ravenswood Media. It shows how government and private agencies have come together to search for solutions to help our bat populations overcome WNS. The public can also play a role in the future of bats by providing habitat and surveying their populations. Bats are a critical component in a healthy forest ecosystem, plus they provide significant agricultural pest control and pollination. Their survival is essential for a sustainable natural environment.


Rabies is a viral infection that is usually transmitted to humans as a result of being bitten by an infected animal. The virus can incubate from two weeks to several months in humans following a bite. Once symptoms appear, the disease attacks the brain and nervous system, eventually killing the victim. If you have been bitten by a bat, wash the wound with soap and water and call your county health agency immediately. Prompt medical treatment and a series of five shots in the arm can prevent a person from contracting rabies.

Bats are not asymptomatic carriers of rabies, which means they can only transmit the virus when they've become sick with the disease themselves. During this stage, a bat's behavior is not normal. Some abnormal behavior includes finding the bat on the ground, activity during the day, or the bat may be unable to fly. The most common way people are bitten by bats is when they pick them up off the ground with bare hands. Like any other wild animal any bat, whether it is sick or healthy, will bite in self-defense if handled.

Bat Rabies in the United States

Rabies is usually found in wild animals such as raccoons, skunks, foxes, coyotes, groundhogs and bats. Reports of rabies in bat populations are uncommon. Statistically, more people are killed by lightening strikes and dog attacks than rabid bats. Over the last 50 years, 40 people have died of rabies transmitted by bats in the United States; 34 were adults and 6 were children.

Testing of these 40 cases determined the variant of bat rabies that caused the illness: Silver-haired Bat/Eastern Pipistrelle was identified in 17 cases, Mexican Free-tailed Bat (8), Silver-haired Bat (8), Big Brown Bat (1), California Bat or Western Small-footed Bat (1), and Eastern Small-footed Bat (1). The isolate was unavailable for one of the human cases and three bat species were not recorded.

Of all these species, the only one that regularly inhabits houses in Maryland is the Big Brown Bat. While the Little Brown Bat is the most frequent user of bat boxes in the United States, it has not been documented to to have transmitted rabies to humans or pets.

- (Source: Bat Conservation International:

Bat Rabies in Maryland

The last reported death in Maryland attributed to bat rabies occurred in 1976. A 55-year old woman was bitten on the hand by a bat; the variant was later identified as Silver-haired Bat/Eastern Pipistrelle Bat. Rabies data from 1991-2000 provided by the Maryland State Department of Health and Mental Hygiene show that skunks, raccoons and foxes (graph below) have the highest prevalence of rabies in Maryland.

Rabies Fact Sheet
(Leaves DNR Website)
Links to Maryland Department of Health and Mental Hygiene

Bats and Rabies - A Public Health Guide
(Leaves DNR Website)
Links to Centers for Disease Control and Prevention
National Center for Infectious Diseases

Bats and Bites

Bats have very sharp tiny teeth that are designed for eating insects. Though bats have tiny teeth, most people know if a bat has bitten them. If you find a bat in your child's bedroom while they were sleeping, in a room with an incapacitated adult person, or in any situation where you are unsure if contact with a bat was made, call your county health agency. If possible, have the bat captured for testing. If no contact has occurred with either humans or pets in the home, the bat can be released outside.

Are bats aggressive and are undetected bat bites an important source of human rabies?

At the 29th Annual North American Symposium on Bat Research, 250 bat researchers from the United States, Canada and Mexico said "no". On October 30, 1999, these researchers voted "...unanimously in support of a resolution stating that they find no credible support for the hypothesis that undetected bites by bats are a significant factor in transmitting rabies to humans... In our collective experience, bats seldom are aggressive, even when sick, and humans typically feel and recognize any bites they receive...The undetected bite hypothesis is not supported by evidence, and it should not drive public policy nor public health responses. We recognize the need for reasonable precautions against rabies, including vaccination of all who handle bats professionally, and public education that: 1) cautions never to handle bats or other animals; 2) warns to seek immediate medical evaluation of any actual or suspected animal bite; and 3) places risks in perspective with values."

The full resolution is available at Bat Conservation International's website,

Tips for Preventing Rabies

  • As required by Maryland law, ensure that all dogs, cats, and ferrets have a current rabies vaccination.
  • Do not feed, handle, or touch wild mammals, stray dogs, or cats.
  • Leave wild animals in the wild. They don't make good pets, and it is against the law to keep them.
  • Never handle a bat with bare hands. Use thick gloves or call a bat removal expert to help you remove bats from your house. See Bats in Houses.
  • Do not let your pets play with bats.


Histoplasmosis is a common, worldwide respiratory illness caused by the fungus Histoplasma capsulatum. This fungus naturally occurs in the soil of areas with warm and humid climates, and wind is thought to be the main agent of dispersal. Bird droppings (particularly of European starlings Sturnus vulgaris, pigeons, and chickens) and bat guano enhance the development of this fungus. Occasionally humans may become infected with this fungus. The majority of human cases reported in the United States (90%) are reported from the Ohio and Mississippi River drainage areas. Bird roosts are the most prevalent source of human infection. Hot, dry attics where bats may roost do not usually provide conditions favorable for fungal growth.

Humans become infected by inhaling airborne fungal spores. Most cases (95% of the 500,000 infections occurring annually in the U.S.) of infection in humans are asymptomatic and do not require treatment.  Others may develop mild, flu-like symptoms. However, a small percentage of people become seriously ill and may die if the illness is left untreated. People who clean up bird or bat droppings should wear a respirator that is capable of filtering out particles as small as two microns in diameter and spray the piles with water prior to cleanup, to reduce airborne spores. Individual homeowners should contact a professional company to remove bat guano or large amounts of bird droppings from attics or other small, confined spaces.