Polio Virus Spreads From Pakistan to Egypt
on 24 January 2013, 12:30 PM
Health officials in Egypt and the world are scrambling to prevent an outbreak of polio after poliovirus from Pakistan was discovered in sewage samples collected at two sites in Cairo in December.
Genetic analysis just completed has linked the Egyptian viruses to one that was last seen in Pakistan in September 2012. How it got to Cairo remains unclear, but the genetic evidence suggests that the virus made the long journey sometime in the past 3 months. Egypt has been polio-free since 2004.
So far, no polio cases have been found in Cairo, and there is no evidence that the virus has established itself and begun to circulate widely. But it's a real risk, says Bruce Aylward, who runs the Global Polio Eradication Initiative (GPEI) from the World Health Organization (WHO) in Geneva, Switzerland.
"The last thing anyone wants is for Eqypt to be reinfected," Aylward says. That's why the country and the international agencies that advise it are treating the positive samples as a fullblown outbreak, "We are being very, very aggressive," Aylward says.
The importation of the virus into Egypt is another setback for the global program, which has finally been making significant progress in the past 2 years, with polio cornered in just three endemic countries: Pakistan, Afghanistan, and Nigeria. (India has now gone 2 years without a single case of polio.) Of the three, Pakistan was doing especially well in knocking out the virus, but the program there has recently been disrupted by the targeted assassination of nine polio workers in December and early January. Those killings, widely condemned, have stoked fears the virus will regain strength in Pakistan and then reinfect polio-free countries. "This is proof positive of long-distance importation from Pakistan, and there may be more," Aylward says.
This is only the second time poliovirus from Pakistan has infected any country other than neighboring Afghanistan; the first was China, where a virus from Pakistan sparked an outbreak in 2011. This new importation puts even more pressure on Pakistan to wipe out the virus within its borders.
The wild poliovirus was detected in untreated sewage water collected on 2 and 6 December as part of routine sampling in the Al Salam and Al Haggana areas in Cairo. Once they were found to be positive, the samples were shipped to the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta for genetic sequencing. The analysis, completed on 18 January, showed that the viruses from the two sites are closely related to each other, and both could be traced to a virus last seen in September in environmental samples in Sukkur in northern Sindh Province in Pakistan.
The presence of the virus in untreated sewage means that a person or several people—maybe a family—carried it from Pakistan and are now excreting it in their stool. No polio cases have been found so far; in general, polio causes paralysis in about one out of every 100 people it infects. Both samples came from the same sewage tributary, says Sona Bari, a WHO spokesperson.
Alerted on Friday night (18 January), WHO, CDC, and other partners in the global initiative immediately sent in teams to help the Egyptian Ministry of Health and Population investigate and plan a response. The have stepped up environmental surveillance and are actively looking for any cases of paralysis that may have been missed. Planning is under way for an emergency campaign to vaccinate children in these two areas of Cairo as soon as possible, to be followed by one in greater Cairo in mid-February and then national campaigns.
Egypt has had two other known poliovirus importations since 2004, but neither caused any illness. A key variable in determining how widely the virus will spread is the population's immunity level. The poliovirus cannot gain a foothold if immunity is high and few kids are susceptible, as is generally the case in Egypt. But experts are worried, Bari says, because Egypt has scaled back its national polio vaccinations campaigns from twice to once a year during the turmoil of the revolution. And even in the best of times, Aylward says, there are always some children who do not receive polio vaccinations, usually in poor populations living in slum areas with inadequate sanitation.
The events come in the week WHO's Executive Board is meeting in Geneva to discuss, among other things, progress and threats to the long-running polio eradication effort, originally scheduled for completion in 2000. "First and foremost on everyone's mind is Pakistan," Alyward says. One issue he expects to be on the table is travel restrictions. The Independent Monitoring Board that oversees GPEI recommended in a November 2012 report that, under the International Health Regulations, the three endemic countries introduce measures to ensure that no one can leave the country without proof of polio vaccination.
Already, Shahnaz Wazir Ali, the Pakistani Prime Minister's focal person for polio eradication, has advised all provincial governments and federal administrations to set up permanent booths in international airports to vaccinate all children under age 5 against polio before they leave the country. http://news.sciencemag.org/scienceinsider/2013/01/polio-virus-spreads-from-pakista.html?ref=hp
