Bats have been linked to a variety of illnesses, including rabies. Furthermore, their droppings, called as "guano," can infect soil with a fungus that causes histoplasmosis, according to the Centers for Disease Control and Prevention (CDC). Bats also spread viral diseases such as rabies and lyssavirus infections. They may also interfere with human activities such as fishing and hunting by eating insects that humans depend on for food. Additionally, they can carry viruses that can be passed on to humans, such as rabies and Hendra virus disease. Bats are also valued because they eat mosquitoes that transmit malaria. However, other animals' behaviors such as making their nests in places where humans live, giving birth to offspring after several months of pregnancy, and leaving their babies behind when migrating seasonally or seeking out new food sources means that bats do not completely solve the problem of mosquito-borne illness. Finally, bats can cause problems by falling into buildings or vehicles or otherwise becoming injured and needing medical attention. They often fail to survive these encounters. Because of their importance in removing pests from our environment, scientists are studying ways to co-exist with bats while protecting humans from their dangers. For example, researchers have experimented with using sound to drive away bats, but this approach has not yet been tested with large colonies.