MONDAY, Dec. 4, 2017 -- Flies aren't just annoying. They can spread disease -- and may be far better at it than scientists previously thought.
Penn State University researchers analyzed the microbiome, or bacterial makeup, of 116 different houseflies and blowflies found across three continents. Both types of flies feed on rotting organic matter and feces, which exposes them to a wide assortment of problematic bacteria.
Some of the flies carried hundreds of different bacteria species, including ones known to be harmful to humans, the researchers found.
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"It will really make you think twice about eating that potato salad that's been sitting out at your next picnic," said study co-author Donald Bryant, a professor of biochemistry and molecular biology.
"It might be better to have that picnic in the woods, far away from urban environments, not a central park," he said in a university news release.
The analysis focused on bacterial content in various fly body parts.
Legs emerged as the most common means of bacterial transmission, the study authors said.
According to study co-author Stephan Schuster, a former Penn State professor, "The legs and wings show the highest microbial diversity in the fly body, suggesting that bacteria use the flies as airborne shuttles. It may be that bacteria survive their journey, growing and spreading on a new surface."
The study found that each step a fly takes leaves behind a microbial colony track, if the new surface supports bacterial growth, Schuster noted.
Bryant added that "this may show a mechanism for pathogen transmission that has been overlooked by public health officials, and flies may contribute to the rapid transmission of pathogens in outbreak situations."
The investigators acknowledged, however, that this transmission route might also play a useful role. For example, it could serve as a kind of early warning system for potentially troubling diseases.
The findings were published recently in the journal Scientific Reports.
More information
There's more on flies and disease at Penn State College of Agricultural Sciences.
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