Although bats themselves are basically harmless, there are definite health risks to consider when bats are living in your home. The first one, and the one that people are most commonly aware of is rabies. Rabies is a viral disease that causes encephalitis, or brain inflammation. It is a disease that can effect both animals and humans, and can be transferred by bats. If a bat has rabies the disease can be transmitted easily, by being bitten by an infected bat, or if the infected bats saliva is transmitted to a human through an open wound, or cut, and if the infected bats saliva comes in contact with a persons nose, eyes, or mouth. If you wake up from sleeping and there is a bat in the room, it is recommended that you get checked out, regardless of whether or not you see any bite marks, or scratches. If possible you should also bring the bat with you to be tested, but avoid direct contact with the bat, and try not to crush or stomp on it for two reasons. Bats are protected by state laws and rabies can be transferred by the blood, urine, or feces of a bat when mixed with spinal fluid, and this happens when the animal is crushed, and therefore makes you more susceptible to infection.
The second health risk you should watch for is called Histoplasmosis. Histoplasmosis is a fungal infection that can be caused by the build up of bat guano, or droppings. Over time, if the bat problem is left to persist, the droppings will accumulate, dry out, and produce spores which can be easily breathed in by human. You should never attempt to remove accumulations of bat droppings by yourself. Histoplasmosis can pose serious health risks, and the removal should always be done by an experienced professional using the proper equipment.
Aside from the health risks involved, the accumulation of bat droppings, and urine can cause serious damage to the insulation in your homes' walls, and attic. If the problem is not remedied it may lead to your insulation needing to be professionally removed, and replaced. That is why we always recommend bat proofing a home before it becomes a problem. Even if you don't have bats it is likely that you possibly could in the future, and its always less costly to prevent a problem, than it is to fix a problem.