KEY POINTS:
Obesity can be caught like a cold, showing that a common infectious virus can turn human cells into fatty tissue, scientists say.
It is well established that the human adenovirus-36 causes respiratory and eye infections but now scientists have discovered that it can also transform adult stem cells
found under the skin into the fat cells of adipose tissue.
The scientists also found that there is a specific gene in the virus that appears to control this fatty transformation, which they observed when human stem cells grown in the laboratory became infected.
The findings were presented yesterday to a meeting of the American Chemical Society.
The research suggested that the growing global epidemic of obesity may involve more than just a lack of exercise and a love of high-calorie food.
"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," said Dr Magdalena Pasarica of Louisiana State University.
"Not all infected people will develop obesity.
"We would ultimately like to identify the underlying factors that predispose some obese people to develop this virus and eventually to find a way to treat it."
Previous research on animals suggested that adenovirus-36 - along with two related viruses known as Ad-37 and Ad-5 - can trigger the tendency to get overweight or obese.
Another study found a high prevalence of adenovirus in overweight people - about 30 per cent of obese people were infected with Ad-36 compared with 11 per cent of lean people.
This led to suggestions that respiratory viruses may play an important role in triggering the tendency towards obesity in susceptible people with the sort of sedentary lifestyle that favours putting on weight.
The latest study appears to support these claims at the cellular level by looking at how the virus interacts with human stem cells growing outside the body in laboratory cultures.
Dr Pasarica obtained the stem cells from fatty tissue which she obtained from a broad cross-section of patients who had undergone liposuction.
She exposed half of the stem cells to Ad-36, while the other half were not exposed to the virus.
After about a week of growing in the laboratory, most of the adult stem cells that had been infected with the virus developed into fat cells whereas the non-infected stem cells did not, Dr Pasarica said. "A common virus appears to target stem cells in humans to generate more and bigger fat cells," Dr Pasarica said.
"The results are clear. Ad-36 prompts adult fat-derived stem cells to convert to pre-fat cells, rather than other cell types.
"Furthermore, these fat cells accumulate lipids - fats - at an increased rate.
"We conclude that human adenovirus Ad-36 increases the number of fat cells and increases their fat content in humans, which might contribute to the development of obesity," she told the meeting.
The spread of obesity around the developed world is one of the fastest growing epidemics today.
However, the idea of it being even partly the result of viral infections is contentious.
Most experts say it is mainly attributable to a change in diet and lifestyle.
- Independent