New study results bolster the controversial hypothesis that certain cases of obesity are contagious. Over the last 20 years, some research has suggested that certain strains of human and avian adenoviruses--responsible for ailments ranging from the chest colds to pink eye--actually make individuals build up more fat cells. Having antibodies to one strain in particular, so-called Ad-36, proved to correlate with the heaviest obese people, and in one study, pairs of twins differed in heft depending on exposure to that virus. Now researchers have identified another strain of adenovirus that makes chickens plump.
Physiologist Leah Whigham of the University of Wisconsin-Madison and her colleagues inoculated young male chickens with three strains of adenovirus--Ad-2, Ad-31 and Ad-37. She and her team then monitored the chickens for three and a half weeks, recording their food intake throughout. Though the infected chickens and noninfected controls consumed the same amount of food and were exposed to the same conditions, chickens carrying Ad-37 were found to have nearly three times as much fat in their guts and more than two times as much fat over their entire body at the end of the three-and-a-half week period. The other two virus strains appeared to have little effect on weight.
"Ad-37 is the third human adenovirus to increase adiposity in animals, but not all adenoviruses produce obesity," Whigham and her fellow authors write in their report presenting the findings in the current issue of the American Journal of Physiology. Although it remains unclear exactly how Ad-37 adds fat, it joins a growing list of such viruses, including canine distemper, Ad-5 and Ad-36.
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Ad-36 has been shown in an in vitro study by researcher Nikhil Dhurandhar of the Pennington Biomedical Research Center to help human cells go from having the potential to store fat to actually storing it. "I am not saying that all obesity is caused by viruses," Dhurandhar notes. "Obesity has multiple causes and viruses may be one of those causes."
Next up for study, Dhurandhar says, is the exact mechanism by which a virus could lead to obesity. This, in turn, might lead to a vaccine that could prevent Ad-36 infections. "We hope to identify the gene or genes that could be responsible for its adiposic effect," he explains. "The long-term goal is to see if we can prevent adenovirus-induced obesity."
Whether or not hand-washing will help with weight management remains to be determined. But two researchers shared a Nobel Prize this past year for their work in uncovering the bacterial root of some ulcers after years of consensus that stress caused the uncomfortable stomach affliction. "It makes people feel more comfortable to think that obesity stems from lack of control," Whigham adds. "It's a big mental leap to think you can catch obesity."
