ISLAMABAD -- Pakistan's city of Peshawar is the world's largest pool of the polio virus, with the vast majority of cases in the country and neighboring Afghanistan tracing back to the restive northwestern city, the World Health Organization announced Friday.
Some 90 percent of polio cases found around Pakistan can be genetically linked to the city, the U.N. organization said. Even 12 of the 13 cases reported in 2013 in neighboring Afghanistan can also be traced back to Peshawar, officials said, showing the challenge of combating the disease in a country where militants target vaccinators.
"If you do not take care of this reservoir it will keep threatening other parts of the country as well. Then the final eradication would be much more difficult," said Elias Durry, who heads the} WHO's eradication efforts in Pakistan.
Pakistan, along with Afghanistan and Nigeria, are the only countries in the world where polio remains endemic.
The WHO announced this week India, which had previously been considered one of the toughest places in the world to eradicate polio because of high-risk communities in remote areas, is to be declared polio-free by the end of March.
Pakistan has struggled for years to eradicate the disease through a series of repeated vaccination campaigns of children.
But that effort has been hampered in recent years by militant attacks that have left more than 30 vaccinators and police officers who protect them dead. Two powerful Pakistani Taliban militants also have banned vaccinators from North and South Waziristan, two tribal regions that border Afghanistan to the west.
The number of polio cases in Pakistan jumped from 58 in 2012 to 91 in 2013. Of the polio cases recorded last year, 65 were located in the remote tribal regions.
Hundreds of thousands of Pakistanis seeking refuge from fighting in the tribal regions in recent years have flooded into Peshawar, which is also the capital of Khyber Paktunkhwa province. Those infected bring the disease back with them when they leave. Hundreds of thousands of Afghans also travel to and from the city daily.
The WHO and the government regularly test samples of the sewage water in Peshawar as well as other major cities across the country. During the last six months, they detected the highly contagious polio virus in all the samples collected in Peshawar, Durry said.
The organization is calling for repeated vaccination campaigns to help get rid of the disease in Peshawar.
Pakistan has been under pressure internationally to eradicate the disease, which usually infects children living in unsanitary conditions. The disease attacks the nerves and can kill or paralyze.
But vaccination teams have had a hard time reaching all children in parts of the troubled northwest. Durry said roughly 260,000 children are believed to have missed vaccinations last year in North and South Waziristan.
Militants claim the vaccine is meant to sterilize Muslim children and accused health workers of being U.S. spies. The allegation gained traction after the CIA used a Pakistani doctor to try to confirm the presence of Osama bin Laden in 2011 under the guise of an immunization program.