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Bats and Public Health
When bats and humans come in close contact, the potential for human disease increases. Bats are capable of transmitting to humans two known diseases: rabies and histoplasmosis. The chances of contracting and then dying from either of these diseases is extremely low. A study that examined a recent 40 year period in the U.S. and Canada uncovered 16 deaths resulting from bat-borne diseases.
Rabies is a viral infection that is always fatal, with only a handful of exceptions, when left untreated. Bats should never be handled. Their only defense mechanism is their bite, which is the primary route for rabies transmission from an infected bat. Rabies is not transmitted thru contact with bat blood, urine or feces. A bat found on the ground, active during the day, discovered in a swimming pool, caught by a dog or cat, or unable to fly is more likely to be infected with rabies.
Histoplasmosis is a fungal infection causing a flu-like respiratory disease. It is contracted by breathing dust stirred up from areas where bat or bird droppings accumulate. The symptoms of histoplasmosis can become severe, and if left untreated can lead to death. Histoplasmosis is not known to exist in California.
Like all mammals, bats are plagued by parasites such as fleas, ticks, mites, bed bugs and flies. Most of these parasites don't leave the bats for other hosts. Often they are host-specific, even preferring a single bat species. Although, if a group or colony of bats is destroyed, after some time the parasites will search for a new host to feed on, this may include you. The key to preventing bat-borne diseases is avoiding bat - human contact. Close associations, where bats roost in areas occupied by humans, pose unacceptable public health risks.
Bats have a poor reproductive potential, producing 1 and rarely 2 offspring per year. This makes it difficult for a population of bats to repopulate after suffering a loss of numerous individuals due to rabies, other natural means or eradication by humans. Therefore when mitigating close human-bat associations, it is not recommended that bats be destroyed. The preferred method is exclusion. Bats roosting in a building occupied or used by humans can be evicted without bringing any harm to them.
At dusk, bats can be seen exiting through their normal access points on their way to begin feeding. Later, during daytime hours, these exit points can be better identified. Bats often enter a building through small cracks under eaves behind chimneys, under a roof shingle or through a hole made by a bird , or rodent. Some openings can be confirmed by the presence of body oils staining the edges of openings or by droppings near or below the opening. Bat droppings can be distinguished from rodent droppings as the older dry droppings easily crush into fine fragments between your fingers. Once the openings have been located, they can then be covered with flashing, 1/4” hardware cloth or plastic netting, excluding the bats. It is important not to trap bats inside a building. By constructing a simple, one-way door at one or two of the exit points, bats will be able to escape, but will not be able to re-enter. The best time to exclude bats is during the late fall or winter months, when adults still feed at night, and when young bats, unable to fly, are not present.
Constructing a one-way door is not as difficult as it may seem. Attach a small plastic tarp or something smooth as a barrier just above the opening with duct tape, staples or by other appropriate means. The use of towels and netting may provide a way for the bats to climb back up to re-enter the opening. The barrier should not hang more than 4 inches out from the opening and should extend a foot or two to either side and below the opening. This will allow an easy exit for the bats, but prevent them from re-entering. Do not attach the barrier at the bottom or along the sides. After discovering they cannot enter, the bats will search for another roosting site. Allow at least one week to pass before assuming that all of the bats have vacated the building and taking more permanent measures to bat proof the building. Repellants such as noise makers, mothballs and metallic streamers have not been proven to be effective. Aerosol repellants are not an adequate substitute for exclusion, and should never be applied or sprayed into an area while bats are roosting.
If you find a dead or sick bat, do not touch or handle it. The bat's likely response will be to bite you. Any sick or dead bat should be treated as if it were infected with rabies. A good way to contain the bat is with a coffee can. Place the can upside down, over the bat. Then slide the lid under the can, forcing the bat inside. The can and the bat can then be kept out of the reach of children, pets and other curious persons. Call local animal control so they can collect the bat and properly assess any possible exposures to potential bites. They will take necessary steps to insure your health and the health of others involved is preserved. If you need help with a bat problem, contact our office. We can provide you with a specific recommendation to help you take action toward eliminating the problem.
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