* Travel restrictions seen ineffective against virus spread
* Unclear why H1N1 swine flu has been so severe in Mexico
* Experts still looking for origin of outbreak
(Adds comments on Mexico severity, vaccines)
By Stephanie Nebehay and Laura MacInnis
GENEVA, April 28 (Reuters) - The World Health Organisation is not recommending travel restrictions and border closures to fight swine flu, a spokesman said on Tuesday.
Infected people may not show symptoms at the airport or when they reach a border crossing, so travel limitations like those imposed during the SARS outbreak are ineffective, spokesman Gregory Hartl said.
"Border controls don't work. Screening doesn't work," he told a news conference, describing the economically-damaging travel bans as basically pointless in public health terms.
Still, the WHO is urging people to think twice before travelling to and from affected areas, and to avoid crowds and public transport in the presence of any flu-like symptoms.
"Certainly if you feel that you are ill you should not travel, in any case, to anywhere," Hartl said.
Up to 149 people in Mexico have died of the new swine flu virus known as H1N1, which has caused milder symptoms in other countries including the United States, Canada, Spain, Britain, Israel, and New Zealand.
"We don't understand why the disease has been more severe in Mexico," Hartl said.
The first victims may not have recognised they were infected with a new type of flu requiring different treatment than normal seasonal flu, they may not have received the required medicines until late, or they may have been infected with other diseases reducing their immunity to the virus, he suggested.
All transmission of the disease so far appears to have been human-to-human and not from animal or other contact, according to the WHO.
"There is no danger form eating pork," Hartl said. "If you cook pork well, if you cook all meat well, it kills all virus."
The WHO does not yet know where the outbreak started from.
"We are still looking for the origin of this event. We don't know where it is, we don't know where the initial infection occurred."
The WHO's emergency committee will not meet on Tuesday to review the pandemic alert level, which was raised on Monday evening to level 4 from 3, on a 1-to-6 scale.
"If the virus is an efficient virus, if it spreads easily from human to human, it will probably continue to spread," Hartl said. "We are still at phase 4 because we do not have incontrovertible evidence this is an efficient spreader." (For more Reuters stories on swine flu, click on [nFLU]) (For more Reuters swine flu coverage, please click here: http://www.reuters.com/news/globalcoverage/swineflu ) (For WHO information on swine flu, go to: http://www.who.int/csr/disease/swineflu/en/index.html ) (Additional reporting by Michael Kahn in London; Editing by Angus MacSwan)
A technician works inside a testing laboratory at the National Center of Infectious and Parasitic Diseases in Sofia April 28, 2009. World governments and businesses announced new steps on Tuesday to ...
