There's fresh concern about a paralyzing, incurable disease that was almost eradicated from the globe. The spread of polio in Asia, Africa and the Middle East poses an international health emergency, the World Health Organization says for the first time. Experts fear that carriers of the contagious viral infection could fly to other countries before they're diagnosed and quarantined. "The current situation stands in stark contrast to the near-cessation of international spread of wild poliovirus" in 2012-13, says the UN-affiliated group.

Decades of efforts to eradicate polio began when vaccines were developed in the 1950s. They reduced the global number of annual cases from hundreds of thousands to under 1,000 now – with none in America. At an emergency meeting in Geneva, the health organization announced 10 countries affected by a new wild polio virus. Pakistan, Syria and Cameroon "pose the greatest risk of further wild poliovirus exportations in 2014," the group warns. in 2012, just 223 new cases were reported worldwide — the lowest ever recorded. Last year, that number exceeded 400.

Until this year, conquering polio had been one of the most successful worldwide public-health efforts. In 1955, 28,985 Americans — mostly children — were stricken with polio. Thanks to a vaccine developed that year by Jonas Salk, and an oral version introduced in 1963, there hasn't been a case of polio on the United States since 1979. Since 1988 more than 2.5 billion children have been immunized worldwide, and the overall number of polio cases has dropped by 99 percent. But in Pakistan, for instance, anti-government Taliban forces oppose vaccinations and attack health care workers.

UN doctor says: "Until it is eradicated, polio will continue to spread internationally, find and paralyze susceptible kids." -- Dr. Bruce Aylward, head of polio eradication at WHO

Medical journalist says: "We're at a crossroads. The world could eradicate polio. . . . Or, we could see a dangerous surge of this virus." – Fergus Walsh, BBC correspondent

World Health Organization says: "The international spread of polio to date in 2014 constitutes an 'extraordinary event' and a public health risk to other states for which a coordinated international response is essential." – May 5 statement