The virus family behind polio also gives you colds and hand, foot and mouth
Enteroviruses are named for the gut, their route into the body, yet they turn up everywhere from the common cold to heart inflammation. Poliovirus was historically the worst of them. Today 84 types are known to cause human disease, and their habit of swapping genetic material even complicates vaccination.
They are small viruses carrying a single strand of RNA about 7,500 bases long, part of the picornavirus family. Once inside a cell, the genome is read as one long protein that viral enzymes then cut into the shell pieces and the replication machinery. Copying is sloppy, so mutation is frequent, and recombination is common too: the copying enzyme can hop between templates mid-task. That can repair damaged genomes and generate diversity, but it also lets live vaccine strains mix with wild relatives, which is how circulating vaccine-derived polioviruses arise.
Early scientists split the group into polioviruses, two kinds of Coxsackie virus and echoviruses, until overlaps made that scheme awkward; newer finds simply get numbers such as EV-D68. Of the 81 non-polio types that infect people, 28 are echoviruses and 22 are Coxsackie A. Coxsackie A16 causes hand, foot and mouth disease, while Coxsackie B viruses can inflame the heart, its surrounding sac, the brain's membranes and the pancreas, usually during warm summer months.
Polio comes in three serotypes, numbered PV-1 to PV-3, whose outer shells differ a little. PV-1 is the commonest, and about 72 percent of infected people show no visible symptoms. Two vaccines exist, an injected inactivated form and an oral one, and together they protect 99 of every 100 children vaccinated. In a quirk of bookkeeping, taxonomists voted by email in 2008 to strip poliovirus of its status as a species and fold it into Human enterovirus C.
Some B-type enteroviruses can mutate into a non-cytolytic form that lingers at low levels indefinitely. Traces have turned up in pancreatic tissue from people with type 1 diabetes, in long-running heart muscle disease and in myalgic encephalomyelitis. Researchers disagree whether this lingering RNA is harmless debris or a driver of those illnesses. EV-D68, first identified in California in 1962, mainly causes respiratory illness in children.
Source: Enterovirus
