An outbreak of deadly swine flu in Mexico and the United States has raised the specter of a new virus against which much of humanity would have little or no immunity. The outbreak of the new multi-strain swine flu virus transmitted from human to human that has killed more than 160 people in Mexico is a “serious situation” with a “pandemic potential”, the head of the World Health Organization said.

US medical authorities expressed strong concern Friday about an unprecedented multi-strain swine flu outbreak that has killed at least 60 people in Mexico and infected seven people in the United States. “It’s very obvious that we are very concerned. We’ve stood up emergency operation centers,” Centers for Disease Control and Prevention (CDC) spokesman Dave Daigle told AFP.

Swine influenza, also mknown as Swine Flu, or Pig Flu, refers to influenza caused by any strain of the influenza virus endemic in pigs (swine). Strains endemic in swine are called swine influenza virus.

The 2009 flu outbreak in humans that is widely known as “swine flu” apparently is not solely due to a swine influenza virus. It is due to a new strain of influenza A virus subtype H1N1 that derives from one strain of human influenza virus, one strain of avian influenza virus, and two separate strains of swine influenza virus. The origins of this new strain are unknown, and the World Organization for Animal Health (OIE) reports that this strain has not been isolated in swine. It passes with apparent ease from human to human, an ability attributed to an as-yet unidentified mutation. The strain in most cases causes only mild symptoms and the infected person makes a full recovery without requiring medical attention and without the use of antiviral medicines.

The World Health Organization went on high alert, dispatching top experts to the United States and Mexico amid concern that the new virus could become a global epidemic.

“It’s a virus that mutated from pigs and transmitted to some humans,” Cordova said earlier.

The US Centers for Disease Control and Prevention (CDC) said tests show some of the Mexican victims died from the same new strain of swine flu that affected eight people in Texas and California, who later recovered.

“It’s very obvious that we are very concerned. We’ve set up emergency operation centers,” CDC spokesman Dave Daigle told AFP.

The WHO said Canadian laboratory testing had confirmed 18 cases of swine fever among almost 1,000 Mexicans found to have an influenza-like illness in three regions — of whom 62 died.

“Because there are human cases associated with an animal influenza virus, and because of the geographical spread of multiple community outbreaks, plus the somewhat unusual age groups affected, these events are of high concern,” the Swiss-based body said in a statement.

“The majority of (the Mexican) cases have occurred in otherwise healthy young adults. Influenza normally affects the very young and the very old, but these age groups have not been heavily affected in Mexico,” the WHO said.