The toll from the swine flu epidemic appears to be stabilizing in Mexico

Concern that the world could be on the brink of the first influenza pandemic in more than 40 years escalated Sunday as France, Hong Kong, New Zealand and Spain reported potential new cases in which people had been infected with swine flu and Canada confirmed several new cases. In the U.S., where 20 such infections have been confirmed, federal health officials declared a public-health emergency and are preparing to distribute to state and local agenciesa quarter of the country's 50 million-dose stockpile of antiviral drugs. Meanwhile, in hard-hit Mexico, where more than 80 people have died from what is believed to be swine flu, the government closed all public schools and canceled hundreds of public events in Mexico City.

The toll from the swine flu epidemic appears to be stabilizing in Mexico, the health secretary said late Tuesday, with only seven more suspected deaths. But an outbreak of the virus at a New York school showed it is capable of repeated jumps between humans — meaning it can keep spreading around the world.

The positive news came even as the first two countries announced travel bans on flights from Mexico, the center of the epidemic, and as confirmed cases were reported for the first time as far away as New Zealand and Israel, joining the United States, Canada, Britain and Spain.

The new virus is suspected in 159 deaths and 2,498 illnesses across Mexico, said Health Secretary Jose Cordova, who called the death toll "more or less stable" even as hospitals are swamped with people who think they have swine flu. And he said only 1,311 suspected swine flu patients remain hospitalized, a sign that treatment works for people who get medical care quickly.

Cuba became the first country to impose an outright ban on travel to the epicenter of the epidemic.

Argentina soon followed with its own ban, and ordered 60,000 visitors who arrrived from Canada, Mexico and the U.S. in the past 20 days to contact the Health Ministry.

Meanwhile, Mexico was eliminating reasons for tourists to visit. On Tuesday, the pyramids and all other archaeological sites were put off limits nationwide and restaurants in the capital were closed for all but take-out food in an aggressive bid to stop gatherings where the virus can spread.

"Border controls do not work. Travel restrictions do not work," said WHO spokesman Gregory Hartl, recalling the SARS epidemic earlier in the decade that killed 774 people, mostly in Asia, and slowed the global economy.

Instead, they say, governments should do more to provide medical help to people with swine flu symptoms, since the virus is proving to be treatable if diagnosed early.

Experts on epidemics said these kinds of government interventions are ineffective, since this flu — a never-before-seen blend of genetic material from pigs, birds and humans to which people have no natural immunity — is already showing up in too many places for containment efforts to make a difference.

Cordova said many of the people crowding hospital waiting rooms complaining of swine flu symptoms actually suffered from other ailments — and many of those suspected of having the virus were treated and sent home.

"You can see the total of new cases," Cordova said, pointing to bar charts that showed a rise and fall. "In the last days there has been a drop."

Cordova said that with U.S. help, new testing facilities in Mexico will soon have the capacity to test 150 samples a day for the new strain of swine flu. Currently, it must send samples to the CDC or Canadian labs, which is the main reason why only 26 of the 159 deaths have been definitively confirmed to be swine flu.

Meanwhile, Cordova said health workers have begun using a less specific quick test, and will immediately administer anti-viral medicine to anyone with the general class of flu that includes the new strain.

Another focus is preventing people from gathering in groups where mass contagion could result. Mexico City's mayor ordered restaurants to limit service to takeouts and deliveries, and closed gyms and swimming pools and restricted access to many government buildings.

In New York, there were growing signs that the virus was moving beyond St. Francis Preparatory school, where sick students started lining up at the nurse's office days after some students returned from Cancun.

At the 2,700-student school, the largest Roman Catholic high school in the nation, "many hundreds of students were ill with symptoms that are most likely swine flu," said Health Commissioner Thomas Frieden. A teacher was one of 28 confirmed cases. And a nearby school with siblings at St. Francis was shut down as well after more than 80 students called in sick.

"It is here and it is spreading," Frieden said.

Rachel Mele, a 16-year-old at the school, saw her fever break Tuesday for the first time in five days. It had been hovering around 101 since the terrifying night when her parents rushed her to the hospital.

"I could barely even catch my breath. I've never felt a pain like that before," Mele said. "My throat, it was burning, like, it was the worst burning sensation I ever got before. I couldn't even swallow. I couldn't even let up air. I could barely breathe through my mouth."

Scientists hope to have a key ingredient for a vaccine ready in early May, but it still will take months before any shots are available for the first required safety testing. Using samples of the flu taken from people who fell ill in Mexico and the U.S., scientists are engineering a strain that could trigger the immune system without causing illness.

"We're about a third of the way" to that goal, said Dr. Ruben Donis of the CDC.

In humans, the symptoms of swine flu are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort. The strain responsible for the 2009 swine flu outbreak in most cases causes only mild symptoms and the infected person recovers fully in a few days.

Of the three genera of human flu, two are endemic also in swine: Influenzavirus A (common) and Influenzavirus C (rare).[2] Influenzavirus B has not been reported in swine. Within Influenzavirus A and Influenzavirus C, the strains endemic to swine and humans are largely distinct.