A vaccine to cut the risk of becoming overweight could be ready for testing within the next five years, according to research that suggests obesity can sometimes be catching.

A common virus may be one factor that contributes to the obesity epidemic sweeping the west, according to the new research.

Although obesity is primarily linked to eating too many calories or burning too few, other factors may play a role, from lack of sleep to changes in stomach bacteria and now a common cold virus.

Scientists in Louisiana showed that infection with human adenovirus–36 (Ad–36), long known as a cause of colds and eye infections, transformed adult stem cells obtained from fat tissue into fat cells, whereas stem cells not exposed to the virus were unchanged.

The study was conducted by Dr. Magdalena Pasarica at Pennington Biomedical Research Center in Baton Rouge, in a lab led by Dr. Nikhil Dhurandhar. In addition, the study reported a virus gene that appeared to be involved in this obesity-promoting effect.

The findings were presented yesterday by Dr. Pasarica to the American Chemical Society in Boston.

Dr. Dhurandhar told the Daily Telegraph that a vaccine aimed at this kind of “infect-obesity” could be ready for tests within five or 10 years.

Dr. Pasarica emphasized that “not all infected people will develop obesity. We’re not saying that a virus is the only cause of obesity, but this study provides stronger evidence that some obesity cases may involve viral infections.”

However, “we first need to prove that Ad–36 causes human obesity.”

Although it would be unethical deliberately to infect people to cause obesity to show the link, evidence for it was growing. “We would ultimately like to identify the underlying factors that predispose some obese people to develop obesity after infection with this virus and eventually find a way to treat it.”

An earlier study — the first to associate a virus with human obesity — found that 30% of obese people were infected with the Ad–36 virus, against just 11% of non obese individuals.

In the new study, Dr. Pasarica and her associates obtained adult stem cells from fatty tissue from liposuction patients. Half the stem cells were exposed to the virus.

After about a week of growth in tissue culture, most of the virus-infected adult stem cells developed into fat cells, whereas the non-infected stem cells did not.

The exact mechanism by which the virus might cause obesity was unknown, said Dr. Pasarica, who did not rule out the possibility that other human viruses may also contribute to obesity.