Poliovirus

Poliovirus is an enterovirus. It is the cause the paralytic disease known as poliomyelitis."

Several outbreaks of what later came to be called myalgic encephalomyelitis were initially misinterpreted as clusters of poliomyelitis or abortive poliomyelitis. Many of the historic outbreaks coincided with confirmed outbreaks of polio including the 1934 Los Angeles outbreak, the 1948 Akureyri, Iceland outbreak, and 1949 outbreak in Adelaide, Australia. However, no serological evidence of polio was ever found and the ultimate pattern of the outbreaks differed in significant ways, chief among them, the tendency to affect adults rather than children, and to result in higher morbidity than poliomyelitis but no mortality.

After the Akureyri outbreak, children in areas that had been affected responded to poliomyelitis vaccination with higher antibody titres, as if these children had already been exposed to an agent immunologically similar to poliomyelitis virus.

It is theorized that exposure to one enterovirus may confer partial immunity or improved immune response to another enteroviruses. One study compared schoolchildren in Estonia, who were inoculated with the Sabin, live attenuated virus polio vaccine, to Finnish schoolchildren, who were inoculated with the Salk, inactivated vaccine. Estonian children had stronger T cell responses to coxsackievirus B4 and poliovirus type 1, and stronger expression of IFN-γ when exposed to poliovirus challenge as compared to Finnish children. Finnish children have weaker cellular immunity against enteroviruses at the age of 9 months compared with Estonian children at the same age. (Finland has a rate of Type 1 diabetes three times the rate of Estonia. Coxsackie B4 has been associated with Type 1 diabetes.) An unintended consequence of widespread polio vaccination may have been impaired immunity to other enteroviruses, such as Coxsackie and echoviruses.