Houseflies on cattle farms may contribute to the spread of Escherichia coli O157:H7 among animals, their food supply and potentially humans say researchers from Kansas. Their findings appear in the December 2004 issue of the journal Applied and Environmental Microbiology.
E. coli, one of the leading causes of food-borne diseases throughout the world, is responsible for more than 73,000 cases annually in the United States alone. E. coli O157:H7 can be life-threatening to children, the elderly and immuno-compromised patients. The intestinal tracts of cattle serve as the main reservoir for E. coli O157:H7 and the environment in which they are housed frequently attracts large populations of houseflies (HF).

“One of the potential modes of dissemination of this pathogen in the environment is by insects that are associated with animal feces and manure, primarily houseflies,” say the researchers.
In the study houseflies were gathered from the feed bunks of a cattle farm in Kansas from June through October 2003. E.coli O157:H7 was found in every batch of houseflies collected, with 30% of the positive houseflies coming from a flaked corn shed. Ninety percent of the isolates contained genes indicating highly virulent strains.
“Our study demonstrated that houseflies carry virulent E. coli O157:H7 in the farm environment primarily during the summer and may play an important role in the ecology and transmission of this pathogen among individual cattle and potentially to the surrounding farm and urban environment,” say the researchers. “Information on the association of E. coli O157:H7 with houseflies will assist in developing more comprehensive and quantitative risk assessments, as well as formulating E. coli O157:H7 intervention strategies that should include an effective HF management program.”
(M.J. Alam, L. Zurek. 2004. Association of Escherichia coli O157:H7 with houseflies on a cattle farm. Applied and Environmental Microbiology, 70. 12: 7578-7580.)