Cases of paralysis in children are being linked to a strain of enterovirus EV-D68, which results in polio-like symptoms in its victims.

Since the summer of 2014, 115 children living in 34 states have fallen into acute flaccid myelitis (AFM), a form of paralysis. The cause of these sudden, unexpected cases has largely been a mystery to medical researchers at this time, and the children have not yet fully recovered.

University of California, San Francisco (UCSF) researchers conducted research suggesting a specific variety of a virus known for decades could be the culprit. Many investigators already believed that the microorganism played a role in this flurry of paralysis cases, although the details were uncertain. This theory was largely based on an increase in cases of EV-D68 among American children at the same time as cases of paralysis started. However, the virus can usually be detected in the spinal fluid of victims, but that evidence has not been found in the most recent cases.

Nasal swabs taken from 25 of the paralyzed children revealed the EV-D68 virus in 12 of the patients. These patients exhibited the B1 strain of the virus, which was first recognized four years ago.

A pair of twins infected with the virus were studied. While one of the siblings developed AFM, the other remained healthy after a bout of respiratory problems. This data, although measured in just a single pair of twins, suggests that genetics could play a significant role in determining reactions to the microorganisms.

"This suggests that it's not only the virus, but also patients' individual biology that determines what disease they may present with," Charles Chiu, director of UCSF-Abbott Viral Diagnostics and Discovery Center, said.

Around 80 percent of the families of victims reported the children developed respiratory problems about six days before the symptoms of AFM were seen. Fevers were also common prior to the loss of muscle strength and control.

Enterovirus 68 was first isolated in California in 1962 and was usually considered a rare disease. However, cases of it have become more common over the last two decades. Last fall a nationwide outbreak of enterovirus D68 caused respiratory illness in 1,153 people, most of whom were children, and left those 115 children paralyzed, despite being a nonpolio enterovirus.

Future research will study the reactions when cells taken from the twins are exposed to the virus, potentially providing details on the role genetics may play in the development of the disease in humans.

"Given that none of the children have fully recovered, we urgently need to continue investigating this new strain of EV-D68 and its potential to cause acute flaccid myelitis," Chiu said.

Analysis of the enterovirus and the role it may play in the recent cases of AFM was published in The Lancet Infectious Diseases.

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