"The spread of polio to countries previously considered free of the crippling disease is a global health emergency, the World Health Organization said, as the virus once driven to the brink of extinction mounts a comeback. Pakistan, Cameroon and Syria pose the greatest risk of exporting the virus to other countries, and should ensure that residents have been vaccinated before they travel, the Geneva-based WHO said in a statement today after a meeting of its emergency committee. It's only the second time the United Nations agency has declared a public health emergency of international concern, after the 2009 influenza pandemic. Polio has resurged as military conflicts from Sudan to Pakistan disrupt vaccination campaigns, giving the virus a toehold. The number of cases reached a record low of 223 globally in 2012 and jumped to 417 last year, according to the WHO. There have been 74 cases this year, including 59 in Pakistan, during what is usually polio's 'low season,' the WHO said. "
