A farm worker in Canada has infected a herd of pigs with swine flu, the first documented case of the virus being passed from human beings to animals.

The herd of pigs tested positive for the H1N1 virus after the worker returned from Mexico with the disease. The herd has been quarantined.

Brian Evans, a senior official from Canada’s food safety agency, said that up to 200 pigs had been infected at the Alberta Farm, and that both the man and pigs are recovering, adding that the virus did not seem to have spread.

He emphasised that there was no food safety concern related to this finding. "The chance that these pigs could transfer virus to a person is remote," he said.

The case adds to growing international concern about the safety of eating pork products, with Russia, China, Indonesia, Ukraine, Philippines and Serbia introducting partial or total import bans of pork from the US.

The UN and World Trade Organisation said on Saturday that there is no justification for such anti-pork trade measures as a result of the swine flu epidemic.

"To date there is no evidence that the virus is transmitted by food," statement said, adding that consumers can safely eat pig products as long as they are prepared hygienically.

Confirmed cases of the swine flu virus now stand at 787 worldwide, with more than half of those in Mexico. Three new deaths reported on Saturday took their death toll to 19, quashing hope that the epidemic’s toll was levelling off.

The World Health Organisation has declared a phase 5 alert level – one step short of declaring a pandemic.

Fifteen cases have so far been confirmed in the UK, including a six-year-old girl from Oxfordshire, who became the youngest Briton to catch the virus. She has made a full recovery, doctors announced today.

A fourth case was confirmed today in Scotland, and fourteen possible cases are being investigated in Wales.

Alan Johnson, the Health Secretary, told BBC One’s The Andrew Marr Show that measures have so far limited the spread of the disease in Britain, but that the country must prepare for the possibility of a more serious, second wave in the autumn.

“We have to not just deal with this outbreak now, but prepare, perhaps, for a second phase further down the line,” he said.

“There will be more cases...there is absolutely no doubt of that. But at the moment all the evidence is that we can confine it, contain it, and treat it effectively.”

China’s response to the first confirmed case of the virus in Asia has meanwhile sparked a diplomatic row with Mexico.

Hong Kong police have blocked access to as city centre hotel in which 300 people are being quarantined after it emerged that a Mexican man suffering from the flu had spent seven hours there.

Health officials and security officers dressed in plastic overalls and masks are providing supplies to the 200 guests and 100 staff, who are to be confined in the MetroPark hotel for seven days.

Panic and frustration mounts among those confined, while in Beijing, Mexicans have also reportedly been confined to a poorly-equipped hotel in the city.

Patricia Espinosa, the Mexican Foreign Minister, criticised the Hong Kong and Beijing authorities for discriminating against Mexicans who show no signs of carrying the virus.

"We are especially worried about China, where Mexican citizens showing no signs at all of being ill, have been isolated, under unacceptable conditions. These are discriminatory measures, without foundation ... The Foreign Ministry recommends avoiding traveling to China until these measures are corrected."

She also condemned Argentina, Peru, Ecuador and Cuba for suspending flights from Mexico due to the flu outbreak.

Mexico traditionally has had good ties with all of those nations. Gavin Smith, a virologist at Hong Kong University, said the quarantine was justified. "With influenza, people are infected before they show symptoms. It seems to me like quite a reasonable measure," he said.

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