But a new "polio-like" virus has the attention of doctors in California. Physicians there are reporting the emergence of an extremely rare virus that presents symptoms similar to those of the infamous child-crippling virus. Over the last 18 months, 20 cases of the new virus have been reported -- mostly in children. Doctors believe the new virus is a strain of enterovirus-68, which is a relative of polio.
Symptoms include restricted movement, weakness in limbs, and in a few cases paralysis of both arms and legs. Enterovirus-68 has previously been most associated with respiratory problems. Doctors recently spoke of their dealings with the newly-identified virus at the annual meeting of the American Academy of Neurology in Philadelphia.
Though the development sounds alarming, doctors say the virus is still extremely rare, and that there is no indication that its spreading more rapidly.
"There has been no obvious increase in the pace of new cases so we don't think we're about to experience an epidemic, that's the good news," Dr. Emanuelle Waubant, a neurologist at the University of California, San Francisco, told the BBC. "But it's bad news for individuals unlucky enough to develop symptoms which tend to be moderate to severe and don't appear to improve too much despite reasonably aggressive treatment."
Jonathan Ball, a professor of virology at the University of Nottingham, told the BBC that enteroviruses related to polio usually just present as a mild cold, and that severe complications like paralysis are rare exceptions.
"Whether or not this strain of enterovirus has caused these or other cases of paralysis is possible but remains conjecture," Ball said, "further studies will be needed to determine this."