According to researchers in the U.S., a virus may be why some people are obese.
A study by scientists at the University of Wisconsin-Madison, has found that the human adenovirus Ad-37 causes obesity in chickens.
The finding supports evidence from other studies that two related viruses, Ad-36 and Ad-5, also cause obesity in animals.
According to Leah D. Whigham, the lead researcher in the new study, human adenoviruses may cause human obesity, but more research is needed before a screening test and vaccine become reality.
She says there is mounting evidence that certain viruses may cause obesity, in essence making obesity contagious, but the viruses that cause human obesity need to be identified before a screening test and vaccine can be developed.
The idea that viruses can cause obesity is contentious says Whigham despite evidence that factors other than poor diet or lack of exercise may be at work in the obesity epidemic.
The study notes that obesity has doubled in adults and has tripled in children in the United States in the last 30 years,and except for infectious diseases, no other chronic disease in history has spread so rapidly.
Whigham says people are more comfortable thinking that obesity stems from lack of control, and a big mental leap is needed to believe obesity is contagious.
As Whigham points out, other diseases once thought to be the product of environmental factors are now known to stem from infectious agents, such as ulcers, once thought to be the result of stress, the bacteria, H. pylori has now been found to be implicated.
The study says the 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.
The Ad-37 virus has been implicated in animal obesity.
The theory is not new as a few decades ago scientists noticed that chickens in India infected with the avian adenovirus SMAM-1 had significantly more fat than non-infected chickens.
The discovery was intriguing then and the explosion of human obesity, even in poor countries, has led to suspicions that overeating and lack of exercise weren't the only culprits.
Since then, Ad-36 has been found to be more prevalent in obese humans.
In Whigham's study the researchers wanted to find out which adenoviruses (in addition to Ad-36 and Ad-5) might be associated with obesity in chickens.
The chickens were separated into four groups and exposed to either Ad-2, Ad-31, or Ad-37.
There was also a control group that was not exposed to any of the viruses.