Ants often carry germs, such as bacteria and fungus, which they pick up as they walk through unsanitary areas, according to University of Missouri Extension. The ants can then transfer these germs to places where food is stored or prepared, which can spread the germs to humans.
Some species of ants have been found to carry disease-causing bacteria, including Streptococcus, Staphylococcus, Salmonella and E. coli, especially in developing countries. These organisms are normally found in feces and can potentially be transferred to humans if the ants come into contact with food or an open wound. There is no evidence, however, indicating that this is a significant risk in the United States, according to University of California Berkeley Wellness.
Although there are more than 450 species of ants found in North America, less than 50 ant species are known to invade homes and regularly come into contact with people, according to University of Missouri Extension. Some of the species most likely to spread germs, due to their behavior and large numbers, are the pharaoh ant and the odorous house ant. Most ant colonies live outdoors and only periodically come indoors to search for food, notes the Illinois Department of Public Health