Learning how flies spread bacteria could spark new methods to track outbreaks

Tiny hairs across the housefly's body allow it to transport and spread bacteria.

When scientists in Singapore sequenced the genes of 116 houseflies, they made a surprising discovery: The bugs carry several hundred types of bacteria, including Helicobacter pylori, which has been linked to stomach ulcers and cancer in people. They believe the finding could be used to recruit flies into health surveillance programs.

The scientific team, led by Nanyang Technological University (NTU) in Singapore, discovered that flies pick up bacteria on their feet, spread them across their wings and then disperse them on surfaces when they land. Because the flies have microscopic hairs across their entire bodies, they can easily catch and transport microorganisms.

The researchers were surprised to discover H. pylori amongst the flies, because that particular bacterium was previously believed to be spread mostly through bodily fluids. They published their research in the journal Scientific Reports.

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The flies were collected using new tools that prevent them from getting contaminated during the process of capturing them. The researchers then sequenced every part of each fly, including the wings and head. They were able to filter the genetic data using a supercomputer to separate genes from the fly’s chromosomes and then compare what was left to all known bacteria stored in databases, according to a press release. That’s how they discovered the bacteria—including H. pylori—that didn’t belong on the flies’ bodies.

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So could flies be used as an early warning of sorts to control outbreaks of disease? The Singapore researchers believe that specially bred flies could be used for that purpose. The insects could be bred to be free of germs, released into the environment and then recaptured using bait. Sequencing their microbiomes would then reveal which bacteria they encountered in that particular area, the scientists proposed. The flies, they said, would act as “autonomous bionic drones.”

"To date, diseases transmitted by a mechanical vector like flies have been a major overlooked pathway by both the medical and academic community,” said Stephan Schuster, a geneticist and professor at NTU in a press release. “This is a great example of how observations from basic research on how diseases spread might be translated into viable and useful applications, opening up new avenues for future technology."

Schuster is one of many scientists interested in learning more about how animals spread disease. A worldwide movement known as One Health has been promoting such studies, hoping to spark research collaborations that shed light on how illnesses are transmitted between animals and people. One such project, launched after the Ebola outbreak in West Africa a few years back, used genetic sequencing data to sort out which species of bat were likely to be able to transmit the disease to people.

NTU’s Schuster believes that in the short term, specially bred flies could be deployed in agriculture as early-warning systems to prevent outbreaks of plant pathogens. With regular monitoring of the flies, he suggested, farmers could identify bacterial invaders and develop targeted treatments that eradicate those pathogens, leaving the rest of the ecosystem untouched.