(WebMD) Viruses may contribute to obesity, new research shows.

Scientists injected three different human viruses -- called adenoviruses -- into chickens. The chickens injected with one of the viruses, Ad-37, developed two to three times more body fat than chickens without the viruses, despite having the same diet. However, the chickens� weight didn�t differ much in the brief trial.

No humans were studied, so it�s not certain if the viruses have the same effect on people.

�The role of adenoviruses in the worldwide epidemic of obesity is a critical question that demands additional research,� write Leah Whigham, PhD, and colleagues.

Whigham works in the University of Wisconsin�s medicine and nutritional sciences departments. Her colleague, Richard Atkinson, MD, now works at Virginia Commonwealth University and heads Obetech, a Virginia company working on blood tests for those viruses.

The findings are published in the American Journal of Physiology -- Regulatory, Integrative, and Comparative Physiology.

Virus + Calories = Obesity?

Obesity has soared worldwide in recent decades. Whigham�s team sees that as a possible clue that viruses are involved.

�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 suggests that adenoviruses could have contributed,� they write.

The idea is controversial. Weight gain is typically understood as being the consequence of consuming more calories than are burned.

Possibly, adenoviruses play a role in that process, suggest Whigham and colleagues. They note that there are currently 51 known types of human adenoviruses, and not all of them produce obesity.

Researchers� Comments

�It makes people feel more comfortable to think that obesity stems from lack of control,� Whigham says, in a news release. She adds, �It�s a big mental leap to think you can catch obesity.�

Only infectious diseases have spread faster than obesity, write Whigham and colleagues.

Frank Greenway, MD, of Louisiana State University didn�t work on Whigham�s study, but he commented on it in a journal editorial.

So far, tests of human antibodies have linked one human adenovirus to human obesity, according to Greenway. Right now, screening large groups of people for antibodies to all human adenoviruses is a �daunting task,� Greenway writes. He calls for better blood tests that could do that job and pave the way for a vaccine.

Even if such a vaccine is created, calories would still count. Virus or no virus, you�ll likely gain weight if you eat more calories than you burn off.

Sources: Whigham, L. American Journal of Physiology � Regulatory, Integrative, and Comparative Physiology, January 2006; vol 290: pp 190-194. Greenway, F. American Journal of Physiology � Regulatory, Integrative, and Comparative Physiology, January 2006; vol 290: R188-R190. News release, American Physiological Society.