MEXICO CITY - A deadly strain of swine flu never seen before has killed as many as 61 people in Mexico and has spread into the United States, where several people were reported ill.

Mexico's government said on Friday that at least 16 people have died of the disease in central Mexico and that it may also have been responsible for 45 other deaths.

The World Health Organization said the virus that killed at least 12 of the victims in Mexico had the same genetic structure as an outbreak discovered in California. [nLO274836]

With the swine flu being passed between people, raising fears of a major outbreak in North America, Mexico's government canceled classes for millions of children in its sprawling capital city and surrounding areas.

It is a virus that mutated from pigs and then at some point was transmitted to humans, Health Minister Jose Angel Cordova said.

It first looked mostly like a swine virus but closer analysis showed it is a never-before-seen mixture of swine, human and avian viruses. [nN24420522]

Humans can occasionally catch swine flu from pigs but rarely have they been known to pass it on to other people.

CLOSE TO 1,000 SUSPECTED CASES IN MEXICO

Seven people have been made ill by the new strain in California and Texas, but all of them have recovered. Mexico said it had close to 1,000 suspected cases there.

Worldwide, seasonal flu kills between 250,000 and 500,000 people in an average year.

The White House was closely following the new cases in the United States and Mexico, and President Barack Obama has been informed, an administration official said.

The Mexican government warned people not to shake hands or kiss when greeting or share food, glasses or cutlery for fear of contracting the flu.

Mexico City, one of the world's biggest cities and home to some 20 million people, was quieter than usual on Friday morning. Normally choking traffic was less chaotic in the absence of school buses and parents driving kids to school.

Many people waiting to enter subway stations had their faces covered with surgical masks.

The virus is an influenza A virus, carrying the designation H1N1. It contains DNA typical to avian, swine and human viruses, including elements from European and Asian swine viruses, the CDC has said. [nN23355101]

The Geneva-based U.N. agency WHO said it was in daily contact with U.S., Canadian and Mexican authorities and had activated its Strategic Health Operations Center (SHOC) -- its command and control center for acute public health events.

Surveillance for and scrutiny of influenza has been stepped up since 2003, when H5N1 bird flu reappeared in Asia. Experts fear this strain, or another strain, could spark a pandemic that could kill millions.

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