Public Release: 

Houseflies May Transmit Ulcer Bug

American Society for Microbiology

WASHINGTON, D.C., May 29, 1997--A staple of summer, the common housefly, may be a reservoir for Helicobacter pylori, the bacterium responsible for some types of ulcers and associated with stomach cancer, say researchers from St. Elizabeth's Medical Center of Boston in the June 1997 issue of the Journal of Clinical Microbiology. This study is the first report of H. pylori colonization of houseflies.

"The mode of transmission of Helicobacter pylori is unknown," says Peter Grübel, one of the authors of the study. "Since viable bacteria have been shown to be excreted in feces from infected individuals and houseflies habitually develop and feed on excrement, we hypothesized that flies ingest and harbor H. pylori and in turn contaminate the human environment."

In the study the researchers exposed groups of adult houseflies to either a culture of the bacteria or a sterile control plate. After exposure, flies were removed from both the sample and the control group and tested at intervals of six hours for the presence of the bacteria on their skin, in their digestive tract, and in their excretions.

The researchers found the bacteria present on the skin of the exposed flies for up to 12 hours. In addition, the exposed flies had bacteria in their gut and their excretions for up to 30 hours after exposure. The control group had no presence of the bacteria.

"We postulate that H. pylori is acquired from human excrement by the housefly, which then, while crawling on human food, contaminates it," says Dr. Grübel.

H. pylori is a bacterium that was first described in the early 1980's by a group of Australian researchers who theorized its connection to ulcers. It is the cause of most duodenal ulcers and an estimated 70-80 percent of gastric ulcers. In the late 1980s researchers at Stanford University showed it was associated with certain types of stomach cancer.

Helicobacter pylori has the unusual ability to live in the harsh acidic environment of the stomach. In most people it causes no disease but in the unlucky few it causes duodenal ulcer, gastric ulcer and gastric cancer.

The organism lives in the stomachs of most people in the world, although in developed countries less than than 50 percent are infected and most children are Helicobacter free. In developing countries infection is almost universal among adults with 50 percent becoming infected by five years of age. A key factor in these differences may be the use of indoor plumbing in developed countries, says Dr. Grübel.

Houseflies frequently come into contact with human food and excrement and have been reported to be involved in the dissemination of numerous diseases including salmonella. Since they habitually produce and feed on excrement and it is now known that they carry the bacterium, it is possible that they can act as vectors in the transmission of H. pylori, says Dr. Grübel.

"Structurally the fly is well adapted for picking up pathogens," says Dr. Grübel. "Its proboscis is provided with a profusion of fine hairs that readily collect environmental detritus. Furthermore each of the six feet of the fly is fitted with hairy structures and pads that secrete a sticky material, thus adding to its pathogen transmission potential. It is therefore not surprising that as many as six million bacteria have been found on the exterior surface of a single feeding fly and more than 100 species of pathogenic organisms have been isolated from the digestive tract of flies."

"The adult housefly can fly as far as 20 miles from its source and can freely enter houses and areas where people congregate, as well as markets, stores, and other places where human food is available. It just as freely frequents human and animal excrement alike," he says.

Dr. Grübel warns that this research only proves that the housefly is capable of carrying the bacterium, and that no definite proof exists that it actually serves as a vector. Future research studies will focus on whether infected flies can actually pass the infection on and determine if H. pylori is present in flies in the wild.

If people still wish to take precautions, though, Dr. Grübel recommends fly control measures, sanitation and plain common sense, like not leaving food sitting out in the open where flies can get to it.

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Dr. Grübel can be reached by phone at (617) 789-2423
or by e-mail at

The Journal of Clinical Microbiology is a publication of the American Society for Microbiology (ASM). With over 40,000 members worldwide, the ASM is the oldest and largest single biological membership organization in the world.

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