By far the main issue when it comes to bats as opposed to other pests is not so much the damage but more so the risk of disease transmission from bats to humans. When bats start to inhabit human environments the risk of a potentially fatal disease being passed to a human is real and, therefore, needs addressing. The diseases most commonly associated with bats are histoplasmosis and rabies.
Histoplasmosis is a respiratory disease that is caused by the fungus Histoplasma capsulatum, which is found in bat droppings. The fungus produces spores that when they become airborne can infect humans by inhalation alone. Symptoms of the disease can be flu-like, to begin with, and also affect in vision, hearing, and the heart’s performance. The illness may further develop into a fever, blood abnormalities, pneumonia, and even death.
By no means do all bats carry the rabies virus, but a small percentage do. When rabies has infected a bat it will make it very sick and so any bat that you encounter flying about could possibly have rabies, though the chances are low.
Bats do not generally attack humans but may attack if humans attempt to capture or handle them, especially if they are rabid or sick. If you or your pet has been bitten by a bat, in particular, a sick bat, you should attempt to catch the bat with tongs, preserve it, and get medical assistance immediately. There is a rabies vaccine that can be effective if given prior to the onset of symptoms; however, once symptoms start to show, the disease is nearly always fatal. In fact, there have been only six known survivors of the rabies virus.