In the hilltop village of La Gloria in eastern Mexico Edgar Hernández plays among the dogs and goats that roam through the streets, seemingly unaware that the swine flu he contracted a few weeks ago — the first known case — has almost brought his country to a standstill and put the rest of the world on alert.

“I feel great,” the five-year-old boy said. “But I had a headache and a sore throat and a fever for a while. I had to lay down in bed.”

Edgar’s mother, Maria, 34, said: “I have very good faith in God, but I was so worried.” She said that her son fell ill after two children in her village died of pneumonia. The cases were dismissed by the authorities as isolated and not related and thus went unreported for weeks.

"I put damp towels on his stomach and forehead because of the fever. I couldn’t sleep because I had to be by his side taking care of him all the time,” she added.

It was confirmed on Monday that Edgar was the first known sufferer of swine flu, a revelation that has put La Gloria and its surrounding factory pig farms and “manure lagoons” at the centre of a global race to find how this new and deadly strain of swine flu emerged.

So far it has killed up to 152 people in Mexico, sickened 2,000 others and spread with remarkable speed around the globe. Attention has so far focused on a pig farm named Granjas Carroll de México, which is a 50 per cent owned subsidiary of Smithfield Foods, based in the US state of Virginia.

Although officials from the World Health Organisation have said that it is too early to pinpoint the origins of the virus, residents of La Gloria have been complaining since March that the odour from Granjas Carroll’s pig waste was causing severe respiratory infections. They held a demonstration this month at which they carried signs of pigs crossed with an X and marked with the word peligro (danger).

“People say it’s Granjas Carroll’s fault because of the pigs,” Ms Hernández said. “Sometimes there are a lot of flies around but here there aren’t pigs. I can’t say anything because I have no evidence that the farms are responsible. I cannot blame anyone . . . I have no explanation for the disease that my son had.”

Other residents in La Gloria are more forthright. José Luis Martínez, 34, said that when he heard about the outbreak on television he recognised the symptoms imediately: fever, coughing, aching joints, severe headaches and, in some cases, vomiting and diarrhoea. Several hundred villagers had been complaining of those ailments since February.

Mr Martínez said: “When we saw it on the television, we said to ourselves, ‘This is what we had’. It all came from here . . . the symptoms they are suffering are the same that we had here.”

Local health officials and José Córdova, the Mexican Health Minister, have downplayed claims that the epidemic could have started in La Gloria, noting that of 30 mucous samples taken from sufferers of respiratory diseases there, only Edgar’s came back positive.

There have been calls to exhume the bodies of the children who died of pneumonia so that they could be tested. The state legislature of Veracruz has demanded that Granjas Carroll release documents about its waste- handling practices.

Smithfield Foods declined to comment on the request, saying that it would not respond to rumours. It has said previously that it has found no clinical signs or symptoms of the presence of swine influenza in its pig herd or in its employees at any of its joint ventures in Mexico.

The company, which supplies the McDonald’s and Subway fast-food chains, was fined $12.3 million (£8.4 million) in 1997 for violating the Clean Water Act.

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