Houseflies Give You Ulcers?

The housefly is a vile creature whose nasty habits--eating feces, regurgitating, and defecating on our skin--can infect us with organisms responsible for salmonella and other diseases. Now scientists have evidence that flies may transmit yet another pathogen: Helicobacter pylori, a bug responsible for up to 80% of gastric ulcers and some stomach cancers.

Ever since Australian researchers first linked H. pylori to stomach ulcers in 1983, scientists have puzzled over how people become infected. The bacteria are ubiquitous, living in the stomachs of about half the people in the world. But "the mode of transmission of H. pylori is unknown," says Peter Grübel, a gastroenterologist at St. Elizabeth's Medical Center in Boston.

Knowing that H. pylori can be cultured from excrement of infected people and that houseflies eat feces, Grübel and his colleagues set out to test whether the housefly (Musca domestica) might be a potential vector. The researchers hatched several hundred flies, half of which were allowed to feed on freshly cultured H. pylori. After 6 hours, the bacterial feast was removed and the flies examined. The researchers found live H. pylori in the guts and excreta of infected flies for as long as 30 hours after the feeding. The control flies, meanwhile, were uninfected. "We postulate that H. pylori is acquired from human excrement by the housefly, which then, while crawling on food, contaminates it," says Grübel, whose group reports its findings in this month's issue of the Journal of Clinical Microbiology.

Other experts point out that the case against houseflies for now is circumstantial: While the pests are capable of transmitting H. pylori, no one has shown that they do. Grübel agrees, adding that his team will look for H. pylori in wild flies and test whether infected flies can pass on the infection to people.