A senior Mexican health official has claimed that swine flu most likely made the jump from a pig to a human in Asia and not at a pig farm in Mexico।
Miguel Angel Lezana, the director of the National Centre for Disease Control, said that genetic information in the H1N1 virus show it is more similar to types of flu that affect pigs in Central and East Asia.
"This corresponds to a Eurasian strain," he said। "It is probable that this strain is not circulating among pigs on the American continent."
Patient zero in Mexico – the earliest known case of the mutant virus - is a five-year-old boy, Edgar Hernandez, who suffered and survived the flu in early March.
Doctors had originally believed he had a traditional strain of flu but after the international outbreak, a stored sample was diagnosed in a US laboratory and came back positive for H1N1.
Edgar lives in La Gloria, a sweltering, dusty village near a largee industrial pig farm, leading many to speculate that this was where the virus had leaped from pig to man.
But Mr Lezana said there was no absolutely no evidence to support this claim.
"It is extremely unlikely that the virus made the mutation in La Gloria," he said।
Mr Lezana said that it is more likely that the virus was carried by people travelling from Asia to the US.
Mexican immigrants could then have brought the virus back home with them, he suggested.
A poor farming community, La Gloria sends many of its residents north of the Rio Grande to work.
Residents of La Gloria have been protesting against the local pig farm for several years, alleging that the waste from the thousands of hogs and piglets has been making them sick.
The allegations have been strenuously denied by the farm's owners.
In February and March, the community was hit with a bout of flu that made hundreds bedridden, including Edgar.
However, Mexican health officials said that samples from other victims show they were suffering from traditional strains of influenza and not the ः१ण१ virus.