A new strain of a polio-like virus is believed to be behind the alarming cases of paralysis reported in children across the US.
The virus called enterovirus C105 belongs to the same polio family of viruses and could be causing the paralysis. Some other viruses are also in the suspect list.
The condition, known as acute flaccid myelitis, leads to muscle weakness or paralysis of arms or legs and has been seen in 100 cases in 34 states.
Initially, a virus called enterovirus D68 (EV-D68) which causes respiratory illness was suspected to be causing the disease but with very few children testing positive for the virus, researchers were looking for other candidates as well.
A six-year-old girl with the acute flaccid myelitis symptoms tested positive for the C105 virus which was found in her respiratory tract.
Symptoms that began with a cold and fever left the child with arm pain that finally led to paralysis. The girl tested negative for EV-D68.
The study should make researchers aware that there is another virus out there that has this association with paralysis, said study co-author Dr Ronald Turner, a professor of paediatrics at the University Of Virginia School Of Medicine. "We probably shouldn't be quite so fast to jump to enterovirus D68 as the [only] cause of these cases," Turner told Live Science.
Hard to detect
The virus, being a new find as also adept at genetic variations, can be hard to detect, he said.
"The presence of this virus strain in North America may contribute to the incidence of flaccid paralysis and may also pose a diagnostic challenge in clinical laboratories," the researchers said in their study, to be published in the October issue of the journal Emerging Infectious Diseases.
However, the study does not prove conclusively the new virus causes paralysis as its presence was detected only in the respiratory tract and not in the spinal cord.
A virus in the respiratory tract may not necessarily cause paralysis, the researchers say.
A global initiative to eradicate poliomyelitis through routine vaccination has brought down the number of cases by more than 99% in 30 years, from an estimated 350,000 cases in 1988 to 650 reported cases in 2011. But major epidemics are still occurring.
More recently, researchers have traced polio outbreaks in the Republic of Congo to two genetic mutations in the virus.