Once close to eradication worldwide, the dreaded disease polio is resurfacing in Muslim-majority countries where vaccinations are hard to come by due to war, religious edicts and ignorance, experts say.
The latest example comes this week in Syria, where a strain of polio originating in Pakistan has crippled more than a dozen children, according to doctors for the Kurdish Red Crescent. Cases have also been showing up in Somalia, Afghanistan and Nigeria.
The problem is prompting some polio-free countries to demand that visitors from high-risk countries take oral vaccines at the airport upon arrival if they cannot prove they've gotten the vaccine.
"The Saudi government has introduced restrictions for all those traveling to the Holy Land from polio-affected countries," said Mazhar Nisar of Pakistan's Ministry of National Health Regulations and Services.
"Every pilgrim is to take polio vaccine before traveling to Saudi Arabia and also upon arrival at any of the international airports in the Kingdom," Nisar said.
Polio is a highly contagious disease caused by a virus in the throat and intestinal tract that can cause paralysis, crippling and even death. It was once the leading cause of disability in the United States and infected millions of people worldwide until the introduction of the polio vaccine in the 1950s.
The disease was eradicated in the United States. Worldwide, there were fewer than a thousand cases and it was headed for total eradication until recently, according to the World Health Organization.
Polio outbreaks have been growing in Pakistan, Nigeria and Somalia, and people from those countries have traveled and spread it elsewhere. More than 1 million children in the Horn of Africa alone have not received polio vaccinations, according to the Polio Global Eradication Initiative.
In Somalia, teams of vaccine workers have been unable to get to children because of impediments brought on by a civil war in which some militant leaders prevent food and medicine from getting to the villages of their enemies. In Nigeria, some parents refuse to let their children be vaccinated unless vaccine groups give the families more benefits.
In Pakistan's Northwest territories, where Taliban clerics have significant influence, polio vaccination teams are maligned as un-Islamic or Western purveyors of poison meant to sterilize Muslim women.
A cleric in Pakistan's Punjab province warned that a jihad would be launched against polio vaccination teams, whose mission he labeled a Western conspiracy, frightening away a team that arrived in Muzaffargarh, according to The Express Tribune.
This week, militants in northwestern Pakistan kidnapped 11 teachers involved in a polio vaccination campaign. Local official Khyali Gul said the teachers were taken from a school in the Bara area, close to Pakistan's northwestern border with Afghanistan.
The United Nations in Pakistan pulled its staff involved in immunization from Pakistan after three eradication workers were shot in Peshawar and two of them were killed, in 2012. Since then, more vaccine teams have been targeted.
Without vaccination, the cases of polio are rising in Pakistan, as is the appearance of the Pakistani strain of polio in other countries where infected Pakistanis travel.
The Pakistani polio virus was found in sewage samples in Israel in June this year (the virus can be found in fecal matter of an infected person) and in Cairo in January.
Thousands of Pakistanis travel to Saudi Arabia every year for the Hajj, the pilgrimage to Islam's holy city of Mecca. And many Pakistanis have been flowing into Syria this year to fight in a civil war against dictator Bashar Assad.
Several cases were confirmed in a province bordering the Kurdish-controlled northeast, says the Kurdish Red Crescent. The United Nations confirmed 10 polio cases in northeast Syria, the first confirmed outbreak of the disease in the country in 14 years. The confirmed cases involved babies and toddlers.
The World Health Organization says the once-rare disease could be resurrected and has declared a polio emergency across the Middle East. Allias Durray, a doctor who is the chief of polio eradication for Pakistan, warned that Europe may be next.
"After the Syrian polio outbreak and the flight of refugees in proximity to Turkey and European Union, it is evident that the polio virus is at the doorstep of Europe," he said.
Not all countries check for polio vaccinations among foreign visitors from countries where polio is considered endemic. The United States requires immigrants be vaccinated, but not visitors.
"We collaborate closely with international organizations and other countries to make sure that international and U.S. guidance on vaccination for immigrants is implemented, said Donda Hansen, media spokesperson for the Center for Global Health at the Center for Disease Control in Atlanta.
"The U.S. maintains 'elimination status' in the U.S. by aggressively investigating every suspected case to determine whether an importation has occurred, taking steps to prevent transmission, and safeguarding Americans," Hansen said.