What's a Picornavirus?


A spacefill model of poliovirus, courtesy of Molecular Aspects of
Picornavirus Infection and Detection, edited by Bert L. Semler and Ellie Ehrenfeld



Well, if you've ever had the common cold, you've probably been in close contact with one of these little buggers. But more specifically, picornaviridae is a family of like viruses who's members have all the following basic characteristics:

Linear, positive sense, single stranded RNA genome
Nonenveloped icosahedron (T=3) made from 60 protomers
Approximately 30 nm or so in diameter (that's small, even for a virus!)
Replication occurs in the cytoplasm
Transmitted by multiple pathways, depending on the genus

An awful lot is known about the picornavirus in general, particularly because of the research spurned by Polio epidemics 1930's and '40's. We know the atomic structures of all but one of the Picornaviridae genera. Although picornaviruses are among the smallest viruses (pico is Latin for "small"--Click here for more picornavirus Etymologies!), it has among its members, a huge variety of pathogens, able to cause Hepatitis A, the common cold, and polio. One of its members is the foot-and-mouth disease virus, which is a huge influence on livestock.

Polioviruses have 11 known proteins. Four of these proteins are used to construct the icosahedral capsid (VP1-4). Another one of these proteins, VPg, is involved in viral replication. Three of these proteins are nonstructural, and are used as proteases, and another is RNA-dependent-RNA polymerase. One picornaviruses enter a host cell, they begin making complementary RNA to their genome (mRNA) in the form of a long polyprotein. This polyprotein, once cleaved, makes up the different viral proteins listed above. Viral replication (See Replication) occurs when the virus uses the mRNA polyprotein as a template to produce a complementary strand of DNA. This strand is genomic material for new viruses. When the viruses are ready to leave the host cell, the cell is destroyed.

Some other random facts: picornaviruses contain no glycoproteins, it has myristic acid, is insensitive to ether, chloroform, and nonionic detergents, is stable at room temperature, and are sometimes unstable at more acidic environments unless stabilized by cations. Picornaviruses have narrow host ranges, and are transmitted horizontally (not passed on from parent to child).

Aside from that, major differences exist between each of the different genera of picornavirus. Although there are five of them, including Aphtoviruses, Cardiovirus, Enterovirus, Hepatovirus, and Rhinovirus, this page will only deal with the three that cause human disease: Enterovirus, Hepatovirus , and Rhinovirus. Check 'em out!

Hepatovirus

Enterovirus

Rhinovirus

Some important viral species affecting humans: polioviruses, coxsackieviruses, echoviruses, rhinoviruses, and hepatitis A virus.

Some important viral species affecting animals: swine vesicular disease virus, bovine enteroviruses, encephalomyocarditis viruses, foot-and-mouth disease viruses, simian hepatitis A virus.

This is an especially imporant virus family because of its ability to cause so many different types of disease in humans. Picornaviruses can affect the human heart, the central nervous system, cause strange bumps all over the body, give you a cold, and damage the liver. For more info on specific diseases caused by the picornavirus family, check these out:

The Common Cold

Polio

Hand-Foot-and-Mouth Disease

Hepatitis A

Cold Quotes

"I sneezed a sneeze into the air
it fell to earth I know not where
but you should have seen the looks on those
in whose vicinity I snoze"

Ish Kabibble

For more quotable cold quotes, click here.