Because flies breed in waste matter and garbage, they can carry and transmit certain types of disease to humans and animals, including dysentery, cholera, E. coli, and other viruses. The germs on a fly's legs and bodies can transfer to your skin or your food; however, it’s rare that you would get sick from one single fly landing. However, the longer a fly spends on your skin or food, the higher the chances are of bacteria and pathogens transmittal.