Bats play a crucial role in our eco-system, but as wild animals, they also pose a potential threat. As an organization that has a mission centered on One Health, we want to seriously address the threats that bats pose to public health. If we better understand these risks, we can better inform conservation efforts that are best for the safety of bat colonies, the public and the environment.
From a One Health perspective, bat species are extremely important to conserve. They are important for controlling insect populations which serve as vectors for other diseases, and they reduce the amount of chemicals being used on our crops which have been shown to introduce other larger public health concerns including harm to pollinator species and contamination of ground water.
A healthy bat population is crucial for a healthy agriculture system. But with deforestation and urbanization, bat populations are facing new threats of habitat loss, and increasingly find themselves in contact with people.
Diseases of Michigan Bats
There are 9 species of bat in Michigan, but the two most common are the Little Brown Bat (Myotis lucifugus) or the Big Brown Bat (Eptesicus fuscus). The Little Brown Bat is more common in the upper peninsula and commonly hibernate in caves. The Big Brown Bat is more common in the lower Peninsula and prefer to hibernate in houses.
The two diseases that are of most concern in these bats are Rabies and Histoplasmosis.
Rabies
Historically bats were considered to carry rabies at a rate of nearly 1 in 10, making them a considerably important reservoir for the rabies virus [1]. More recent sampling has shown that rabies prevalence in bat populations is much lower than once thought, occurring in a small fraction of a percent of bats. In addition, some bats seem to harbor rabies at higher rates. Less than 1 percent of Big Brown Bats have been shown to test positive for rabies. Little Brown Bats are thought to harbor rabies at a much lower rate suggesting that they are not a significant reservoir for rabies variants [2].
Even though the percentage of bats carrying rabies is extremely small, the threat that rabies poses to people is very high, so it remains imperative that the threat any rabies vector species poses be well understood. Once someone begins showing signs for rabies, the virus has a near 100% mortality rate.
For this reason, if there is any suspected contact between a bat and a non-vaccinated person, the bat should be captured, humanely euthanized and submitted for rabies testing.
Catching a Suspected Bat
Any contact with a bat warrants submitting the bat for rabies testing. This means if a bat was in the same room as someone who was sleeping, inebriated, or otherwise impaired, or in the same room with an infant, or someone otherwise unable to communicate whether the bat had bitten them or not, or if someone has handled a bat without the use of thick leather gloves.
If you suspect contact with a bat, it is imperative that you catch the bat with the below guidelines:
- Close all doors and windows to isolate the bat
- Don’t take your eyes off the bat
- Always use gloves (preferably leather)
- Cover the bat with a coffee can or shoe box
- Slip something over the top to trap the bat
Call the Michigan Department of Health and Human Services (MDHHS) at (517) 335-8067 to find out how you can submit the bat for rabies testing.
This should be done as soon as possible because, if the bat is positive, any people who have had contact with the bat should be treated for rabies with a special Post-Exposure Vaccine. If administered soon after exposure, these vaccines are highly effective at protecting people against rabies infection.
Histoplasmosis
This is not a disease carried by bats directly but is a fungus that can grow in areas where there is a large accumulation of bat droppings. As it relates to bats, one of the most common sites is attic spaces containing large maternal colonies of bats. These bats can produce a significant number of droppings known as guano. The high nitrogen content provides a good growth medium for histoplasma fungus.
The spores to this fungus can become airborne when the droppings are disturbed and are harmful if inhaled. People who are especially at risk are the elderly, children or anyone with a compromised immune system.
We recommend that guano or droppings in attics be handled with great care. If removing guano from an attic space, the use of a respirator is essential to reduce the risk of contracting this disease.
In healthy, immune competent adults, the symptoms are usually flu like symptoms that are in most cases self-limiting and will resolve within 1 week.
[1] Klug B, Turmelle A, Ellison J, Baerwald E, Barclay R. RABIES PREVALENCE IN MIGRATORY TREE-BATS IN ALBERTA AND THE INFLUENCE OF ROOSTING ECOLOGY AND SAMPLING METHOD ON REPORTED PREVALENCE OF RABIES IN BATS. JOURNAL OF WILDLIFE DISEASES. 2011;47:64-77.
[2] Sharon L. Messenger, Jean S. Smith, Charles E. Rupprecht; Emerging Epidemiology of Bat-Associated Cryptic Cases of Rabies in Humans in the United States, Clinical Infectious Diseases, Volume 35, Issue 6, 15 September 2002, Pages 738–747, https://doi.org/10.1086/342387