Flies more germ-laden than thought

You may want to rethink gobbling down those potato fries that have been sitting out at your next picnic as according to a team of researchers, the disease-carrying potential of flies may be greater than previously thought.

In a study of the microbiomes of 116 houseflies and blowflies from three different continents, researchers found, in some cases, these flies carried hundreds of different species of bacteria, many of which are harmful to humans. Because flies often live close to humans, scientists have long suspected they played a role in carrying and spreading diseases, but this study, which was originally initiated at Penn State's Eberly College of Science, added further proof, as well as insights into the extent of that threat.

"We believe 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," said researcher Donald Bryant.

The researchers were able to investigate the microbial content of individual fly body parts, including legs and wings. The legs appear to transfer most of the microbial organisms from one surface to another, he added.

Blowflies and houseflies, both carrion fly species, are often exposed to unhygienic matter because they use feces and decaying organic matter to nurture their young, where they could pick up bacteria that could act as pathogens to humans, plants and animals.

The study also indicated that blowflies and houseflies share over 50 percent of their microbiome, a mixture of host-related microorganisms and those acquired from the environments they inhabit. Surprisingly, flies collected from stables carried fewer pathogens than those collected from urban environments.

The researchers found 15 instances of the human pathogen Helicobacter pylori, a pathogen often causing ulcers in the human gut, largely in the blowfly samples collected in Brazil. The known route of transmission of Helicobacter has never considered flies as a possible vector for the disease, said Schuster.

The potential, then, for flies to carry diseases may increase when more people are present.

"It will really make you think twice about eating that potato salad that's been sitting out at your next picnic," Bryant said. "It might be better to have that picnic in the woods, far away from urban environments, not a central park."

Researcher Ana Carolina Junqueira said that the novel genomic and computational methods used for the study allowed the team an unprecedented look at the microbial community carried by flies.

Flies may not be all bad, however. The researchers suggested they could turn into helpers for human society, perhaps even serving as living drones that can act as an early-warning system for diseases.

The study appears in journal Scientific Reports.