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.
"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
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 6 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.
How It Happens
"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
1980s by a group of Australian researchers who theorized its connection
to ulcers. It is the cause of most duodenal ulcers and an estimated 70%
to 80% 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
The organism lives in the stomachs of most people in the world, although
in developed countries less than 50% are infected and most children are
Helicobacter free. In developing countries, infection is almost
universal among adults, with 50% becoming infected by 5 years of age. A
key factor in these differences may be the use of indoor plumbing in developed
countries, says Dr. Grübel.
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.