Can You Catch Obesity?

Could a virus spread weight gain, just as it spreads colds and flu? Obesity scientist Dr. Nikhil Dhurandhar was working in Bombay, India in the 1980s when a strange virus began wiping out hundreds of thousands of chickens. When the chickens died, they were abnormally heavy.

Scientists identified the infectious agent as an adenovirus called SMAM-1. When Dr. Dhurandhar infected other chickens with the same virus, they gained weight. Then he injected several other types of animals with a similar human adenovirus called Ad-36, and they also gained weight. Although it would have been too risky to inject humans with the virus, Dr. Dhurandhar was able to test for the presence of Ad-36 in humans. In a study group of 500 people, 30 percent of those who were obese tested positive for the virus, compared with only 5 to 10 percent of people who were not obese.

Dr. Dhurandhar thinks Ad-36 might cause obesity by increasing the size and number of fat cells in the body. He is looking at the possibility of a vaccine that might protect against this "fat virus." However, the rest of the medical community isn't convinced that such a virus exists. They argue that viruses don't tend to leave permanent damage to the body - they just cause infections and go away. They contend that obesity is primarily caused by an unhealthy diet and a lack of exercise.

Ghrelin and Immune Response

The "fat vaccine" is under investigation by Cytos, a Swiss biotechnology company. Currently called CYT009-GhrQb, the vaccine's purpose is to create an immune response in the body against ghrelin, a peptide (a short chain of amino acids, the building blocks of proteins) released by cells in the stomach. Scientists don't know exactly how ghrelin works, but several studies have shown that it stimulates appetite. In one study of anorexic patients, people given ghrelin were hungrier and ate more than those given a placebo. Blood levels of ghrelin quickly rise after people lose weight, which may be why so many people have trouble keeping the weight off. Studies have also indicated that bariatric surgery works, in part, because ghrelin levels drop when the stomach has been reduced.

The CYT009-GhrQb vaccine instructs the immune system to release antibodies that attach to ghrelin and hold it in the bloodstream. This keeps the peptide from making its way into the brain and triggering the feeling of hunger.

But will the vaccine actually cause people to lose weight?