Viruses may leave a weighty legacy.

It all started 7 years ago with a chance remark by a Bombay veterinarian.

Discussing some diseased chickens with nutritionist Nikhil V. Dhurandhar, the vet mentioned a puzzling observation. Within a few days of contracting what would prove a lethal virus, his birds began to gain weight. Over a mere 3 weeks, the chickens gained 60 to 75 percent more fat than did chickens that were not infected.

"I became curious," recalls Dhurandhar, now at the University of Wisconsin Medical School in Madison. Dhurandhar started probing whether this fattening infection has a human corollary. This week, he reported startling data suggesting that viral infections may indeed play a role in some human obesity.

The Bombay chickens had been infected with SMAM-1, an avian adenovirus. This virus has not appeared in the United States, so when Dhurandhar arrived in Wisconsin, he began working with AD-36, a related adenovirus.

Last October, at a meeting of the North American Association for the Study of Obesity, he and his Wisconsin colleague Richard L. Atkinson reported finding not only that AD-36 provokes rapid obesity in chickens but that, like SMAM-1, it leaves infected birds with "paradoxically low serum cholesterol and triglycerides." Ordinarily, fat birds, like fat people, develop elevated concentrations of cholesterol and triglycerides in their blood; both are potent risk factors for heart disease.

Because AD-36 can also infect people, inducing coldlike respiratory symptoms and diarrhea, the Wisconsin researchers decided to screen men and women for antibodies to the virus. The volunteers included 45 lean individuals and 154 obese persons, weighing in at about 250 pounds each.

None of the lean men or women had the antibodies, but 15 percent of the obese volunteers did carry these telltale markers of prior infection. What's more, among the obese, only those with antibodies to the adenovirus had cholesterol and triglyceride concentrations well within the normal range. Men, but not women, with the antibodies lost 1.6 times the weight in a reduction program than those without antibodies. Dhurandhar reported the findings this week in New Orleans at Experimental Biology '97, a meeting of seven research societies.

In chickens, AD-36 infection alters metabolism such that, even with the same food and exercise, infected birds gain more weight than uninfected ones. Because obese people suffer discrimination and tend to have a poor self-image, linking their portliness with something besides gluttony or inactivity "can, emotionally, be quite important," Atkinson says.

Establishing whether such a link exists will be difficult, however, requiring prompt culturing of newly infected persons and tracking of their weight. If there is a tie, Atkinson says, there will be tremendous impetus to develop a vaccine.

For now, the Wisconsin researchers have formed a company and applied for federal approval to market a test for the antibody.