There are more than 100 pathogens associated with the housefly, which makes it a major transmitter for diseases. The pathogens are carried on the mouthparts and the whole body are spread because the flies vomit on solid food items in order to predigest them. In addition to this, they also defecate regularly on food.

Among the many diseases that are spread by flies are Cholera, dysentery, typhoid, tuberculosis, salmonella poisoning and parasitic worms. The larvae of some fly species are known to infect human flesh through open wounds causing myiasis.