Although in early stages, the findings could lead to the development of a 'fat vaccine,' reducing the mounting pressure on food manufacturers, who have been held largely responsible for the disease.
The study, which now reveals that obesity could be contagious, appeared in the January issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.
Scientists led by Leah Whigham at the University of Wisconsin, Madison, revealed that the Ad-37 virus- one of around 50 known human adenoviruses- causes obesity in chickens. The findings build on previous studies that examined how two related viruses, Ad-36 and Ad-5, also cause obesity in animals.
According to the authors, although the notion that viruses can cause obesity is a contentious one among scientists, their evidence suggests that the spread of the epidemic is not only a result of people's eating and exercise habits.
"The prevalence of obesity has doubled in adults in the United States in the last 30 years and has tripled in children. With the exception of infectious diseases, no other chronic disease in history has spread so rapidly, and the etiological factors producing this epidemic have not been clearly identified," said the authors.
"The nearly simultaneous increase in the prevalence of obesity in most countries of the world is difficult to explain by changes in food intake and exercise alone, and suggest that adenoviruses could have contributed," they added.
Whigham noted that 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.
"It makes people feel more comfortable to think that obesity stems from lack of control. It's a big mental leap to think you can catch obesity," she said.
In the latest study, the scientists separated chickens into four groups, exposing three of these groups to different adenovirus types. The fourth control group was not exposed to any viruses. The researchers measured food intake and tracked the weight of the chickens for three weeks.
Out of the four groups, chickens inoculated with Ad-37 had "much more" body fat compared to the other groups, although the amount of food they consumed was the same.
The scientists concluded form their findings that Ad-37 is the third human adenovirus known to increase body fat in animals, but added that not all adenoviruses produce obesity.
"The role of adenoviruses in the worldwide epidemic of obesity is a critical question that demands additional research," they said.
Indeed, Whigham noted that there is still much to learn about how these viruses work.
"There are people and animals that get infected and don't get fat. We don't know why," she said, adding that one possibility could be that the virus creates a tendency to obesity that must be triggered by overeating.
And if further research confirms the findings that obesity in humans could be 'contagious,' the next step would be to develop a vaccine to prevent people getting fat.
"If a vaccine were to be developed, one would want to ensure that all the serotypes of human adenoviruses responsible for human obesity were covered in the vaccine," said Frank Greenway, professor in the Department of Clinical Trials at Louisiana State University, Baton Rouge.