Houseflies have evolved in close association with people and their environment. While houseflies are plentiful and annoying, of greater importance is their role in possible transmission of organisms, which cause diseases and illnesses such as typhoid, cholera, dysentery and diarrhea. They can also mechanically transmit parasitic worms such as pinworms, roundworms and hookworms. The houseflies' filthy habits make them efficient in picking up disease causing organisms from garbage, sewage and fecal matter. They regurgitate, defecate or simply transfer those organisms by leg or mouth to human and animal food.