Obesity linked to virus, new experiments suggest
July 28, 2000
Web posted at: 2:35 PM EDT (1835 GMT)
(AP) -- A cold-like virus may cause obesity, new experiments
suggest.
Researchers at the University of Wisconsin in Madison have found
that mice and chickens infected with a common human virus put on
much more fat than uninfected animals. They have also discovered
that the same virus is more prevalent among overweight people, a
strong indication that it may also cause obesity in humans.
In four experiments, the Wisconsin researchers inoculated chickens
and mice with adenovirus-36, a member of a viral family that
includes about 50 strains. Most adenoviruses cause colds, diarrhea
or pinkeye.
After several months, animals infected with adenovirus-36 weighed
only 7 percent more on average than those without the virus, but
their bodies contained more than twice as much fat.
"This is the first human virus that has been shown to cause obesity
in animals," said Nikhil Dhurandhar, one of the study's
authors.
It is also the first virus the researchers looked at, raising the
possibility that other human viruses may also cause obesity.
Dhurandhar and his colleagues picked adenovirus-36 simply because
little is known about it and the strain is relatively easy to work
with.
Their study is being published in the August issue of the
International Journal of Obesity.
"It raises a host of very interesting questions," said John Foreyt,
an obesity expert at Baylor College of Medicine. "If it really does
play a role I think it's a real breakthrough."
The latest results do not indicate that all obesity is caused by
viruses, Foreyt said. But they strongly suggest that infection
plays an important role.
"There's just so much more we need to do on this before we can say
anything definitive," said Richard Atkinson, a University of
Wisconsin professor and author of the study.
Unpublished studies in humans show that 20 to 30 percent of
overweight people are infected with adenovirus-36, compared to
about 5 percent of the lean population.
Experts are not completely surprised by the Wisconsin group's
results. In the last few years, they have found signs that many
chronic health conditions are caused by infections. Three different
microbes are thought to contribute to clogged arteries. Long
thought to be a product of high stress and a poor diet, ulcers are
now known to be caused by the bacterium Helicobacter pylori.
In addition, several animal viruses are already known to cause
obesity in both animals and humans. But adenovirus-36 is the first
human virus known to cause an increase in fat.
Researchers do not know yet how adenovirus-36 causes obesity.
Infected animals did not eat more than uninfected ones, suggesting
that the virus decreases energy expenditure rather than increasing
appetite.
"I feel that it increases the number of fat cells, which encourages
them to store more fat," said Dhurandhar, who recently joined Wayne
State University in Detroit.
The animal obesity viruses appear to work differently from
adenovirus-36, by damaging the part of the brain that controls
appetite. The Wisconsin researchers saw no brain damage in chickens
and mice infected with adenovirus-36.
Aside from a day or two of cold-like symptoms, Atkinson said, the
virus produced no observable effects besides obesity.
Paradoxically, animals infected with the virus also had decreased
levels of cholesterol and triglycerides in their blood. Generally,
obesity is associated with high cholesterol and triglyceride
levels.
Far more research is needed before any practical benefits can be
reaped from this research, Atkinson said. It is still too early to
know whether it may be possible to develop an effective vaccine
against obesity or otherwise counteract the effects of the
virus.
(WHO'S NEXT TO CATCH THE FAT VIRUS?! 
)