Common cold virus causes polio symptoms in mice

A common cold virus closely related to the virus that causes polio can produce polio symptoms in mice, U.S. researchers reported on Tuesday.

Their findings suggest that wiping out polio - a real possibility with the global vaccination campaign underway - may not rid the world of the paralyzing symptoms of the virus.

The team of virologists at Duke University Medical Center stumbled onto their finding when working with a virus called coxsackievirus A21.

Instead of developing a cold, mice injected with the virus unexpectedly developed the paralysis characteristic of polio.

"In principle, coxsackieviruses could cause polio in humans," said Dr. Matthias Gromeier, who led the study.

"We are in the process of eradicating polio worldwide, but if we eliminate the poliovirus and cease polio vaccinations, our immune systems wouldn't produce antibodies against polio, and coxsackievirus could theoretically fill the niche of eradicated polio."

Writing in the Proceedings of the National Academy of Sciences, the researchers said world health officials need to study the possibility.

Virus experts have widely believed that while related, coxsackievirus and poliovirus cause different illnesses because they bind to different docking sites, called receptors, on cells they infect.

Poliovirus is usually inhaled or ingested.

"We gave the coxsackievirus a distinct advantage by injecting it directly into muscle, where it had direct access to the kinds of nerve cells polio normally attacks," said Gromeier. "The resulting polio symptoms were milder than those caused by the poliovirus, but it was polio nonetheless."

This is precisely the kind of adaptable behavior that makes viruses so dangerous, Gromeier said.

"Our study reveals how similar these viruses actually are," he said. "It is fascinating that a minor change such as injection site may cause a harmless cold virus to attack the central nervous system."

Gromeier's team is now working with the U.S. Centers for Disease Control and Prevention to test coxsackievirus samples from patients around the world to see which genes are involved in causing polio-like symptoms.

Polio once killed and paralyzed millions of children a year. The virus is incurable and affects mostly children under 5. In 1988, when the World Health Organization launched the Global Polio Eradication Initiative, there were 350,000 cases. Last year, thanks to vaccination efforts, there were fewer than 800 cases worldwide, all restricted to six countries.

SOURCE: Proceedings of the National Academy of Sciences, September 7, 2004.