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Mysterious cases of paralysis in children in the United States may be caused by a previously rare virus spread by sneezing and coughing, according to doctors.

More than 100 children and young adults in the US and one child in France have been taken to hospital with unexplained weakness and paralysis in their limbs, known as acute flaccid paralysis (AFP), since September last year.

A condition, more commonly associated with the polio virus, had been known to cause similar symptoms, but since the virus was eradicated it has become rare.

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Enterovirus D68, the structure of which is shown above imposed upon a black and white electron microscope image of the virus, is now the prime suspect in clusters of mysterious limb paralysis in children in the USA

The recent outbreak of AFP has alarmed doctors and they now believe another, unknown virus may be causing the condition.

Researchers found that a cluster of children suffering from ongoing paralysis despite treatment in Aurora, Colorado had also suffered from infections of respiratory viruses within three months of their condition appearing.

The scientists found that almost half the children had been infected by a previously rare virus called enterovirus D68 (EV-D68), which is distantly related to polio.

These children were also found to have damage to the neurons in their spinal cord and in their brainstem.

The researchers now believe this virus could be behind 107 other unexplained cases of paralysis that have been reported across the USA and a further case reported in France.

Dr Samuel Dominguez, a microbial epidemiologist at the Children's Hospital Colorado, who led the research, said: 'The extent to which this new distinctive neurological disease has spread is unknown, but it does not appear to be isolated to Colorado or the USA.

'If further investigation confirms the link between EV-D68 and AFP and cranial nerve dysfunction, EV-D68 will be added to the list of non-poliovirus enteroviruses capable of causing severe, potentially irreversible neurological damage, and finding effective antiviral therapies and vaccines will be a priority.'

First identified in California in 1962, it is known to cause mild symptoms of fever, sneezing and runny nose, but was rarely seen.

However, since August 2014 it has been linked to more than 1,000 respiratory infections through out the USA.

The researchers in Colorado, whose findings are published in the Lancet tested 12 children who had been admitted to hospital with unexplained paralysis in their limbs.

They found that eight of the children had suffered from a respiratory viral infection before being affected, five of which were identified as EV-D68.

While the findings do not conclusively prove that EV-D68 is responsible for the paralysis, there is other circumstantial evidence.

Other cases of paralysis have appeared during wider outbreaks of EV-D68. Researchers detected EV-D68 in nasal swabs from 8 out 41 people with paralysis who were tested.

There are also signs that the virus has been mutating from its original form since it first appeared in the 1960s.

Scientists at Purdue University in Indiana are now attempting to develop a treatment to combat infection by the virus.

They performed X-ray crystallography of the virus and found that its protective shell contains a pocket that helps it infect cells.

This image shows enterovirus D68 while bound to an antiviral compound called pleconaril (shown in orange). Researchers are working on new antiviral molecules that might work against more recent strains of the virus

They found that it is possible to bind a molecule within this pocket to prevent this infection from happening.

Professor Michael Rossman, who is leading the work, said they are now hoping to find compounds that might bind to the virus in this way and could be safely taken as drugs.

One antiviral drug, known as pleconaril, was found to act against early strains of the virus, but is ineffective against more recent strains.

Professor Rossman said: 'Designing the best possible compound for these newer strains will take more time, but I hope that in a year or so we might have something.'