Obesity may be contagious

American scientists have found evidence that viruses can cause obesity, advising people to wash their hands to avoid becoming overweight.

A team from the University of Wisconsin, Madison, found that the human adenovirus Ad-37 causes obesity in chickens.

The discovery builds on studies that two related viruses, Ad-36 and Ad-5, also cause obesity in animals.

Ad-36 has also been associated with human obesity, leading researchers to suspect that Ad-37 may be implicated as well.

The notion that viruses can cause obesity has been a contentious one among scientists, said Dr Leah Whigham, lead author of the study.

However, there is evidence that factors other than poor diet or lack of exercise may be at work in the obesity epidemic, she added.

"With the exception of infectious diseases, no other chronic disease in history has spread so rapidly," said Dr Whigham.

"The nearly simultaneous increase in obesity in most countries is difficult to explain by changes in food intake and exercise alone, and suggest that adenoviruses could have contributed."

Other diseases once thought to be the product of environmental factors are now known to stem from infectious agents.

For example, ulcers were once thought to be the result of stress, but researchers eventually implicated bacteria, H. pylori, as a cause.

The authors said further research is needed to confirm whether Ad-37 causes obesity in humans as previous studies have been inconclusive.

"Ad-37 is the third human adenovirus to increase adiposity in animals, but not all adenoviruses produce obesity," the study concluded. 

The findings are reported in the American Journal of Physiology.

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