A researcher of Indian origin residing in the U.S has said that the obesity bug can be passed on from other people's cough, sneeze and unclean hands.
Professor Nikhil Dhurandhar, of Pennington Biomedical Research Centre in Louisiana, believes that an airborne "adenovirus" germ may be causing the fat plague that is blighting Britain and other countries.
He reckons that about one in three obese people might have become overweight after falling victim to the highly infectious cold-like virus, known as AD-36.
The researcher says that the virus-which is known to cause coughs, sore throats, diarrhoea and conjunctivitis-has of late been found to make fat cells multiply, leading to weight gain.
While genes are thought to make some people more susceptible to weight gain, the current study suggests that infections could also hold the key.
Chickens, mice and monkeys infected with AD-36 have been found to put on weight quicker than uninfected animals in previous studies.
Recent findings in humans suggest that 33 per cent of obese adults had contracted AD-36 at some point in their lives, compared with only 11 per cent of lean men and women.
Professor Dhurandhar said that AD-36 continued to add weight gain long after those infected had seemingly recovered.
His research suggested that the virus lingers for up to three months, during which time it multiplies fat and is contagious to others.
"We now know that this virus goes to the lungs and spreads to various organs such as the liver, kidney, brain and fat tissue," the Daily Express quoted the researcher, who will make the extraordinary claims on BBC2's Horizon tonight, as saying.
"When it goes to fat tissue it replicates, making more copies of itself and in the process increases the number of new fat cells, which may explain why people get fat when they are infected with this virus," he added.
While some medical experts welcomed the findings, others sounded a note of caution.
Dr Shahrad Taheri, clinical director for obesity at the Birmingham Heartlands Hospital, said: "Most people believe obesity is caused by environmental factors. But there is a lot of information about how things like the furring up of arteries could be linked to infections. It is not beyond reason to think about various different factors, including infections, adding into the mix about what causes obesity."
Tony Barnett, professor of medicine at the University of Birmingham, said: "These associations may give some clues but they detract from the basic message that we all need to take more exercise and eat a bit less. This kind of research needs to go on but we have to be cautious."