Flies transmit over 65 known human and animal diseases via mechanical transmission.
The legs, body hairs, and mouthparts of a fly pick up pathogens when they come into contact with feces, garbage, and carrion, and then transfer these pathogens when they fly onto human food and kitchen surfaces.
A typical fly transmission pathway: a fly first feeds on a pile of dog feces, its hairy legs becoming smeared with bacteria, then flies to your kitchen and lands on a sandwich.
Within the few seconds it is stopped, the fly contaminates the food in three ways: direct transfer of pathogens from its legs onto the food surface; regurgitation of digestive enzymes (which may contain pathogens from previous meals) while feeding; and defecation while eating (flies defecate every few minutes).
Diseases transmitted by flies include: Salmonellosis, Shigellosis (bacillary dysentery), Cholera, Typhoid fever, _E.
coli_ infections, and various parasitic infections (roundworm, hookworm).
The house fly is listed by the World Health Organization as one of the most important public health pests.