From Egypt's order that all 300,000 pigs in the country be slaughtered to travel bans and putting the kibosh on kissing, the world is taking drastic _ and some say debatable _ measures to combat swine flu.

Egypt ordered the pig slaughter even though there hasn't been a single case of swine flu there and no evidence that pigs have spread the disease. Britain, with only five cases, is trying to buy 32 million masks. And in the United States, President Barack Obama said more of the country's 132,000 schools may have to be shuttered.

At airports from Japan to South Korea to Greece and Turkey, thermal cameras were trained on airline passengers to see if any were feverish. And Lebanon discouraged traditional Arab peck-on-the-cheek greetings, even though no one has come down with the virus there.

All this and more, even though world health experts say many of these measures may not stop the disease from spreading. On Wednesday, the World Health Organization raised its pandemic alert to the second-highest level, meaning it believes a global outbreak of the disease is imminent.

"Scientifically speaking, the main thing is that every virus behaves differently," said Joerg Hacker, president of the Robert Koch Institute, Germany's top public health authority. "At the moment, the main issue is to get to know this virus, how it works."

In Germany, where officials confirmed three cases, Lufthansa announced that starting Thursday it will put a doctor aboard all flights to Mexico, the epicenter of the outbreak.

Experts said that makes sense: The doctors will be able to field questions from uneasy passengers and tend to anyone who might fall ill.

The World Health Organization said total bans on travel to Mexico _ such as one imposed by Argentina, which hasn't had any confirmed cases _ were questionable because the virus is already fairly widespread.

Roselyne Bachelot, France's health minister, said she would ask the European Union to suspend all flights to Mexico at a meeting Thursday in Luxembourg.

Travel bans were effective during the 2003 outbreak of SARS in Asia, because that illness can be transmitted only by people who already show symptoms. With flu, by contrast, the incubation period ranges from 24 hours to four days, meaning people often are infectious before they have symptoms.

Health officials don't know enough about swine flu right now to say what the precise incubation period is, but if it's similar to other flu, people are likely able to spread it before they're sick.

"WHO does not recommend closing of borders and does not recommend restrictions of travel," said Dr. Keiji Fukuda, the Geneva-based organization's flu chief. "From an international perspective, closing borders or restricting travel would have very little effect, if any effect at all, at stopping the movement of this virus."

Nor will killing pigs, as Egypt began doing Wednesday, infuriating pig farmers who blocked streets and stoned Health Ministry workers' vehicles in protest. While pigs are banned entirely in some Muslim countries because of religious dietary restrictions, they are raised in Egypt for consumption by the country's Christian minority.

Unlike bird flu, where the H5N1 strain that spread to humans was widespread in bird populations and officials worried about people's exposure to infected birds, WHO says there is no similar concern about pigs _ and no evidence that people have contracted swine flu by eating pork or handling pigs.

"There is no association that we've found between pigs and the disease in humans," WHO spokesman Dick Thompson said.

But that hasn't stopped governments from banning pig products. Macedonia ordered a halt to all live pig imports and on Tuesday, Mexico City closed down all its popular streetside taco stands for at least a week.

Dr. Nikki Shindo, a WHO flu expert, said the agency will consider requests to stop calling the disease swine flu, since the virus is not food-borne and has nothing to do with eating pork.

U.S. Agriculture Secretary Tom Vilsack and others have suggested a new name, arguing that swine flu implies a problem with pork products. China, Russia and Ukraine are among countries that have banned pork imports from Mexico and parts of the United States affected by swine flu.

But some anti-flu measures have merit, such as Obama's admonition Wednesday that more American schools might have to be closed temporarily if swine flu cases spread. Already tens of thousands of students in Texas, New York, California, Chicago and elsewhere are out of school.

The WHO said closing schools and public places, along with banning or restricting mass gatherings, can be a way to contain the spread of disease. Epidemiologists call it "social distancing," and the idea is simple: If you keep people who have the virus away from others, you can stop the chain of transmission.

"That's a technique we would be recommending in a pandemic," said WHO's Thompson. "We would recommend it to nations as a useful technique to be applied given the special circumstances of each nation."

Officials in Hong Kong, which has no confirmed cases, said workers were scrubbing public toilets every two hours in an effort to improve hygiene.

"Not only will we be stepping up our usual efforts, but also we will make special efforts to make sure that our back alleys, public housing estates, recreation and transportation facilities are thoroughly cleansed and disinfected," said Gabriel Leung, undersecretary for the Food and Health Bureau.

Experts, however, said it's debatable how much good disinfecting public places will do. It probably helps cut down on bacteria and kill viruses lurking on surfaces, but it's unclear whether it would stop person-to-person transmission.

Ditto the advice to stop kissing on the cheek, which was among the earliest measures _ along with refraining from handshakes _ to be recommended by authorities in Mexico.

WHO's Thompson was noncommittal on the "don't kiss" advice, saying only: "There are different national circumstances that health officials are going to know far better than we will. It's up to them to make that call."

But at a news conference announcing the elevated pandemic level, WHO chief Margaret Chan went further, suggesting it was time to rethink the traditional three kisses on the cheek popular in Switzerland and elsewhere in Europe. "Perhaps instead of having the traditional three hugs to say hello and welcome your friends, maybe you don't do that anymore," she said. "Don't hold each other and hug their face three times."

The flu virus is airborne and spread through tiny particles _ mostly through sneezing and coughing. That helps explain why governments worldwide have been distributing millions of face masks, even though the U.S. Centers for Disease Control and other agencies have questioned their effectiveness.

Some doctors warn masks might even be harmful, causing people to take risks _ like venturing into crowds or neglecting to wash hands _ in the mistaken belief the mask protects them. More expensive high filtration masks like those used by health professionals can filter out fine particles carried in the air, but even these must be used properly to give real protection.

Other measures, such as installing thermal cameras at airports to screen passengers from infected countries, are simply inconclusive. Scanners were set up across Asia during the SARS outbreak, but officials aren't sure they caught any cases. WHO says the usefulness of such devices is debatable.

Amid the flurry of measures being taken, fear mingled with a sense of fatalism.

"You can't protect yourself _ not in the way that people are traveling nowadays," said Karin Henriksson, 56, of Stockholm.

"Then you would have to put the entire population in quarantine. And you can't do that, can you?"

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Kole reported from Vienna; Cheng, an AP Medical Writer, from London.