From Scientific American:
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.
Whether or not hand-washing will help with weight management remains to be determined.
More here.