From VOA Learning English, this is the Health Report.

The World Health Organization has declared the Pakistani city of Peshawar the world's "largest reservoir" of endemic polio virus. And WHO officials fear Pakistanis could face travel restrictions unless steps are taken immediately to stop the disease from spreading.

Researchers studied all the cases of poliomyelitis in Pakistan last year. The researchers found that almost every case could be linked genetically to the polio virus often reported in Peshawar.

They added that all test samples collected from different parts of the city have shown the presence of the highly infectious virus. Polio mainly affects children under 5 years of age.

The virus is passed through food or water. The virus reproduces in the body and later invades the nervous system. The disease can sometimes lead to paralysis with loss of muscle control in part of the body.

The WHO study found that 90 percent of Pakistan's polio cases could be linked to the virus in Peshawar. In addition, 12 of the 13 polio cases in Afghanistan were also linked to the city.

Elias Durry serves as the WHO's emergency coordinator for polio in Pakistan. He says local officials need to take urgent action to strengthen vaccination campaigns. He says the situation in Peshawar not only threatens the gains Pakistan has made against polio, but could also harm international efforts to stop the disease.

"Unless the polio eradication program in Pakistan is able to curtail the transmission in Peshawar, the expansion of the viruses to other places will not stop. So, it is critical that Peshawar, the way it is behaving now, really be able to find ways of interrupting these transmissions that have been consistent throughout the years," said Durry.

He also noted an increase in deadly attacks on vaccination campaign workers in and around Peshawar and in other areas.

Taliban militants often attack polio workers in Pakistan. The militants accuse them of being American spies or part of a plot to keep Muslims from having babies. Most of the attacks have taken place in Peshawar because the city is close to the country's tribal districts. Extremist groups have bases in those areas.

Elias Durry did not reject the possibility of other countries ordering travel and visa restrictions on Pakistan if there is no quick improvement in the situation.

In neighboring India, no polio cases have been reported for the past 3 years. Starting this month, all visitors to India from Pakistan are required to show a record of their polio vaccination.