* Polio is highly contagious, children especially at risk
* Geneva meeting to assess consequences of recent outbreaks
By Kate Kelland
LONDON, April 28 (Reuters) - The World Health Organisation (WHO) began an emergency meeting with experts on Monday on how to halt the spread of the crippling polio virus across international borders in Asia, Africa and the Middle East.
Polio passes easily from person to person and can spread rapidly among children, especially in the kind of unsanitary conditions endured by displaced people in war-torn regions, refugee camps and areas where healthcare is limited.
"Wild polio virus continues to spread internationally from both endemic and re-infected countries," the United Nations health agency said in a statement, adding that the meeting in Geneva would last several days.
Health experts from North America, Europe, Asia, Africa and the Middle East will be asked "to advise on whether the current developments on the spread of polio virus constitute a public health emergency of international concern", it said.
Polio re-emerged in Syria in 2013 for the first time in 14 years, fanning fears of a wider international proliferation and prompting a vast regional emergency vaccination campaign.
The virus invades the nervous system and can cause irreversible paralysis within hours. The WHO has repeatedly warned that as long as any single child remains infected with polio, children everywhere are at risk.
There is no cure for the disease but it can be prevented by immunisation. The polio vaccine, administered multiple times, can protect a child for life.
Although transmission of indigenous polio has been declining substantially in endemic areas since 2012, a total of 10 countries are currently considered to have active polio transmission. Three of these - Afghanistan, Pakistan and Nigeria - are still endemic for the disease and seven are countries that were once polio-free but have been re-infected.
Between January and April 2014, in what is usually the low season for polio transmission, three new cases of the virus crossing international borders have occurred - from Pakistan into Afghanistan, from Syria into Iraq and from Cameroon to Equatorial Guinea in central Africa.
"The Emergency Committee will provide advice ... as to whether this increasing international spread of polio is a public health emergency of international concern and, if so, whether temporary recommendations are needed to reduce the risk and consequences of international spread," the WHO said.
It gave no details on what those measures might be, but said it would update its advice at the end of the Geneva meeting. (Editing by Gareth Jones)