Polio-free countries still face threat, scientists say

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Published November 21, 2013

| LiveScience

An outbreak of polio in a previously polio-free region of China shows that the crippling, potentially deadly disease will remain a global threat as long as the poliovirus circulates anywhere in the world, scientists say.

Researchers who investigated the outbreak of polio in the Chinese province of Xingjian in 2011 found the infection was caused by a poliovirus that originated in Pakistan, according to the study published Nov. 20 in The New England Journal of Medicine.

"Global eradication of poliomyelitis will benefit all countries, even those that are currently free of poliomyelitis," the researchers wrote in their study.

Polio, or poliomyelitis, is a highly contagious and incurable viral infection of the nervous system. While some people recover completely, the virus causes lifelong paralysis in one out of every 200 cases. [7DevastatingInfectious Diseases]

In the 1980s, the virus killed or paralyzed around 350,000 people worldwide each year. But now, due to vaccination campaigns, the disease is eradicated in most parts of the world. Polio remains endemic in only three countries: Afghanistan, Nigeria and Pakistan. In 2012, about 220 cases were reported worldwide, and almost all were in these countries.

Despite the progress, imported poliovirus has caused outbreaks in some previously polio-free countries in recent years, and scientists have found that the virus is circulating in some regions that had previously been declared polio-free, the researchers said.

In October, an outbreak of polio that affected at least 22 people was reported in Syria, and was a setback for a country that had a vaccination rate of 95 percent and was polio-free for 14 years. The outbreak is possibly being fueled by disrupted vaccinations amid the ongoing civil war in the country.

Experts warned that the disease might reach Europe as well, especially in regions where vaccination coverage is not sufficiently high; for example, Austria (83 percent) and Ukraine (74 percent). The World Health Organization recommends a target vaccination rate of 90 percent.

The outbreak in China struck in 2011, and affected about 40 people, according to the new study. A public health emergency was declared in Xinjiang, and health practitioners closely watched for any new case of sudden paralysis or "acute flaccid paralysis," the signature symptom of polio, the researchers said.

Five rounds of vaccination with oral poliovirus vaccine were conducted among children and adults in the region, and the outbreak was stopped six weeks after the first case had been confirmed by lab results.

"The response most likely prevented poliomyelitis from spreading to other parts of China," but given the fact the poliovirus still circulates in parts of the world, immunization and surveillance efforts should be boosted, the researchers said.

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