While houseflies can be annoying, and are prone to entering homes where they sometimes establish nuisance infestations, the common airborne insects are not often considered to be a source of human disease. Unfortunately, the common housefly, Musca domestica, is not a medically innocuous insect species, as numerous people have, and will continue to fall victim to numerous diseases as a result of making physical contact with pathogen-rich houseflies, and by eating foods that have been exposed to contaminated houselfies.
Some arthropod species can carry disease-causing pathogens that thrive and multiply within their bodies. These arthropod species are known as “biological disease vectors,” and they pose a serious public health threat in nearly every populated region of the world. The most threatening biological arthropod vectors in the United States include several mosquito and tick species, many of which are abundant in the northeast. Houseflies, on the other hand, become exposed to dangerous pathogens within filthy environments. These pathogens do not thrive in concert with a housefly’s physiology; instead, the pathogens simply remain on the fly’s external body where they can be transported to humans, and human food sources upon contact. Therefore, houseflies are not biological disease vectors; instead, houseflies are “mechanical disease vectors.”
According to decades of medical research, houseflies can carry over 100 disease-causing pathogens that include numerous species of bacteria, viruses, fungi and parasites. Houseflies are well known to dwell and breed within pathogen-rich conditions, including areas where feces, rotting animal carcasses, rotting food sources and other decaying organic materials can be found. The types of pathogens carried by houseflies differ by global region, but many studies have found well over a dozen different disease-causing pathogens on flies captured outdoors in the US. These pathogens include bacterial species, such as E. coli, S. dysenteriae, K. pneumoniae, Vibrio cholera and five species of Staphylococcus, including Staph. aureas. Even more alarming, houseflies can become exposed to all of the above named bacterial pathogens within human-inhabited conditions, including homes and restaurants. Indoor bacterial pathogens likely originate from rotting food and outside garbage bins and dumpsters. Another study showed that lab-reared houselfies are capable of carrying several species of Salmonella and the B. anthrax bacteria species. Luckily, Salmonella and B. anthrax have not been found on wild houseflies in the US. In addition to the pathogens listed above, houselfies in the US can also carry viral, parasitic and fungal pathogens, such as Picornavirus, Hookworm and Aspergillus, respectively.
Are you concerned about the health consequences associated with an abundance of indoor flies?