Enteroviruses are a genus of single-stranded RNA viruses. The best-known enterovirus is the one that causes polio, but there are about 100 strains of non-polio enteroviruses as well; EV-D68 is one of them. Enteroviruses generally enter their victims via the respiratory system, producing primarily flu-like symptoms. But in some patients, EV-68 appears to migrate to the nervous system, where it causes partial or full paralysis of one or more limbs. The nervous system damage caused by EV-68 is not always reversible, and many of the children infected last year still have symptoms of paralysis from their infections.
So, we now know the cause. That's the first step; now we need a cure.