When babies receive shots against diseases like polio and measles, their vaccinations may in the future include protection against getting fat, according to researchers. Infection by certain pathogens triggers rapid increases in fatty tissue in animals, Nikhil Dhurnadha told the annual meeting of NAASO, the Obesity Society, in this western Canadian city.

At the same time, the discovery that many more obese people than normal-weight people have been exposed to a certain virus suggests a link between obesity and viral infection. "Not all obesity can be explained by infection," said Dhurandhar, of the Pennington Biomedial Research Center at Louisiana State University in Baton Rouge. "Infections can be one of the causes." Popular opinion has long held that most obesity is caused simply by overeating, underexercise and a lack of will power. But viruses are just one of many contributing factors that scientists have recently discovered.

Researchers are reporting at the conference on other fat triggers that include a genetic tendency to store fat among groups whose ancestors survived famines, medications such as treatments for psychotic mental disorders, toxins in the environment like organochlorines, and infectious agents like bacteria, viruses and prions.

"Obesity is multifactoral," Dhurandhar told scientists at the conference. In an interview with AFP, he said there is proof that at least 10 different pathogens cause obesity in animals. They include canine distemper virus, RAV7 and MAM1 avian viruses, the Borna virus in rats -- which is also linked with depression in humans, types of scrapie, three adeno viruses including AD5, AD36 and AD37 which cause fat gain in several species, and chlamydia pneumonae bacteria. Scientists have also found that when mice are infected by general bacteria from the guts of other mice, the recipients body fat increases.

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"In 10 years, people may be able to walk into a clinic and be told that their obesity is due to X cause, such as genes, the endocrine system, or pathogens. That may have a more productive outcome than a blanket treatment right now, (which) is not very successful," said Dhurandhar. And because viruses are hard or impossible to treat, he said, prevention through vaccines will be key.