MEXICO CITY -- Global health authorities warned Wednesday that swine flu was threatening to bloom into a pandemic, and the virus spread farther in Europe even as the outbreak appeared to stabilize at its epicenter. A toddler who succumbed in Texas became the first death outside Mexico.

New cases and deaths finally seemed to be leveling off in Mexico, where 160 people have been killed, after an aggressive public health campaign. But the World Health Organization said the global threat is nevertheless serious enough to ramp up efforts to produce a vaccine against the virus.

Celia Can, wearing a respiratory mask, is greeted by her daughter, Cleofe Marquez, at Sky Harbor International Airport in Phoenix, Wednesday, April 29, 2009. Can arrived from Hermosillo, Mexico, and was wearing the mask as a precautionary measure against the swine flu. [Agencies] more photos

"It really is all of humanity that is under threat during a pandemic," WHO Director General Margaret Chan said in Geneva. "We do not have all the answers right now, but we will get them."

It was the first time the WHO had declared a Phase 5 outbreak, the second-highest on its threat scale, indicating a pandemic could be imminent.

The first US death from the outbreak was a Mexico City toddler who traveled to Texas with family and died Monday night at a Houston hospital. US Health and Human Services Secretary Kathleen Sebelius predicted the child would not be the last US death from swine flu.

The virus, a mix of pig, bird and human genes to which people have limited natural immunity, had spread to at least nine countries. In the United States, nearly 100 have been sickened in 11 states.

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Eight states closed schools Wednesday, affecting 53,000 students in Texas alone, and President Barack Obama said wider school closings might be necessary to keep crowds from spreading the flu. Mexico has already closed schools nationwide until at least May 6.

"Every American should know that the federal government is prepared to do whatever is necessary to control the impact of this virus," Obama said, highlighting his request for $1.5 billion in emergency funding for vaccines.

Just north of the Mexican border, 39 Marines were being confined to their California base after one contracted what may be swine flu. Senators questioned Homeland Security Secretary Janet Napolitano about her decision not to close the border, action she said "has not been merited by the facts."

Ecuador joined Cuba and Argentina in banning travel either to or from Mexico, and other nations considered similar bans. In France, President Nicolas Sarkozy met with cabinet ministers to discuss swine flu, and the health minister said France would ask the European Union to suspend flights to Mexico.

The US, the European Union and other countries have discouraged nonessential travel to Mexico. Some countries have urged their citizens to avoid the United States and Canada as well. Health officials said such bans would do little to stop the virus.

Germany and Austria became the latest countries to report swine flu infections Wednesday, with cases already confirmed in Canada, Britain, Israel, New Zealand and Spain.

In addition to the 160 deaths, the virus is believed to have sickened 2,498 people across Mexico. But only 1,311 suspected swine flu patients remained hospitalized, and a closer look at daily admissions and deaths at Mexico's public hospitals suggests the outbreak may have peaked during three grim days last week when thousands of people complained of flu symptoms.

Scientists believe that somewhere in the world, months or even a year ago, a pig virus jumped to a human and mutated, and has been spreading between humans ever since. Unlike with bird flu, doctors have no evidence suggesting a direct pig-to-human infection from this strain, which is why they haven't recommended killing pigs.

Medical detectives have not zeroed in on where the outbreak began. Mexico's chief epidemiologist suggested Wednesday that someone could have carried it in from Pakistan or Bangladesh -- or just about anywhere else in the world.