Flies and Salmonella: A Bad Combo in Poultry Houses

Flies may be more than a mere nuisance. They may also spread food poisoning bacteria like Salmonella enteritidis to chickens and their eggs.

Agricultural Research Service (ARS) microbiologist Peter S. Holt and entomologist Christopher J. Geden found that the common housefly, Musca domestica, readily picks up bacteria from its surroundings. When the chickens eat the flies, the bacteria get inside the birds. Holt works in the Egg Safety and Quality Research Unit at the ARS Richard B. Russell Research Center in Athens, Ga., while Geden is at the ARS Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

In three experiments, Holt placed chickens in individual, adjacent laying cages. Geden delivered fly pupae just 48 hours short of hatching as flies; this timing ensures the flies aren't exposed to any microbe prior to emergence. The fly pupae were placed in an open box in the bird room. Three days later, hens were orally infected with Salmonella.

The researchers detected the bacteria in and on 45 to 50 percent of the flies within the first 48 hours of the flies' hatching.

Next, uninfected hens were exposed to the newly infected flies. Just being around the flies didn't cause healthy birds to become infected, but eating infected flies did. This showed that simple physical contact may not be the primary method of transfer of Salmonella bacteria to different surfaces in a poultry house. But, according to the researchers, a hen's eating of contaminated flies does seem to be the primary mechanism of transmission of Salmonella from flies to birds.

According to Holt, this shows that flies in poultry houses are not only a nuisance, but also a threat to the safety of poultry products.

Read more about the research in the March 2008 issue of Agricultural Research magazine.