the alleged culprit is human adenovirus-36,or AD-36.A study published in 2002 showed that AD-36 injected into monkeys causes dramatic weight gain.In some animals,the injected virus caused body fat to triple.It's unethical to inoculate people with viruses,of course.But in an analysis of 1000 people, the scientists found that those with AD-36 antibodies-a sign that they have been infected-are significantly more likely to be overweight.