The obesity explosion that has swept the Western world during the past 30 years may have been caused by a virus, scientists have said.
Researchers have discovered new evidence for an illness they have called "infectobesity" - obesity that is transmitted from person to person, much like an infection. The agent
thought to be responsible is a strain of adenovirus, versions of which cause the common cold. It has already been labelled the "fat bug".
There are more than 50 strains of adenovirus known to infect humans but only one, adenovirus 36, has been linked with human obesity.
Now scientists at the University of California, San Diego, have found that children who showed evidence of infection with adenovirus 36 were more likely to be fat.
In tests on 124 children aged 8 to 18, the virus was present in more than 20 per cent of those who were obese, compared with less than 6 per cent of the rest. Among those infected with adenovirus 36, four out of five were obese.
Children carrying the virus weighed on average almost 23kg more than those who were not. Among the obese children, who accounted for half the total, those with the virus weighed on average 16kg more than the rest.
Jeffrey Schwimmer, an associate professor of clinical paediatrics, who led the study published in the US journal Pediatrics, said: "This amount of extra weight is a major concern at any age, but is especially so for a child.
"This work helps point out that body weight is more complicated than it's made out to be. And it is time that we move away from assigning blame in favour of developing a level of understanding that will better support efforts at both prevention and treatment."
The idea of a viral cause for obesity was first raised a decade ago by Nikhil Dhurandhar, now a professor at the Pennington Biomedical Research Centre in Louisiana. He noticed that chickens which died during a flu epidemic in India in the 1980s - caused by an adenovirus - were plump, rather than thin as expected.
Sceptics pointed out that viruses had never been linked with a long-term disorder such as obesity. Dr Dhurandhar said the evidence was as clear as a map of the US - where the obesity epidemic "has spread like a forest fire from the east coast to the west over the last 20 years".
