A picornavirus is a member of the Picornaviridae family of viruses, which are some of the smallest RNA viruses known to exist. Their single strand of RNA contains only a few thousand base-pairs - half that of influenza viruses like the H1N1 "swine" flu virus of 2009, and a miniscule percentage of the several billion base-pairs found in human DNA. There are a large number of picornaviruses which infect both humans and several animal species, causing such conditions as foot-and-mouth disease, the common cold, the stomach flu, and hepatitis. The name literally means "small RNA virus," using the Latin word pico for "small."
The Picornaviridae family is divided into twelve groups, or genera (the plural form of "genus," commonly used in biological taxonomy). One of these, the enteroviruses, includes a number of particular viruses which cause respiratory tract infections (the common cold) and gastrointestinal or digestive tract infections (the stomach flu) in humans, as well as coxsackie A and coxsackie B viruses (which can cause a range of illnesses, such as meningitis, Bornholm's disease, and outbreaks of rashes and blisters known as hand, foot and mouth disease).
Another genus, Hepatovirus, includes the virus that causes hepatitis A, a potentially serious liver disease in humans. (Note that the common cold can actually be caused by a number of viruses, not all of which are found in this family.) The genus also includes the virus which causes polio (poliomyelitis). Polio killed and deformed millions of children during the twentieth century, and continues to cause harm in areas where there is no ready access to the polio vaccine.
There are also quite a number of picornaviruses that infect various non-human animal species. The aphthoviruses are a group of picornaviruses which affect livestock, including the dreaded foot-and-mouth disease which caused a worldwide agricultural scare several years ago. Another form, the cardiovirus, spreads in mice but rarely jumps to humans. Other aphthoviruses cause different infections in cattle (bovine rhinitis) and in horses (equine rhinitis). Another genus, Avihepatovirus, even causes a hepatitis-like liver condition in ducks. Some picoranviruses even affect plants, not animals. These have been classified separately by taxonomists, as the Secoviridae.
Today, there are highly effective vaccines to combat polio, rendering this formerly dread disease unheard-of in the developed world. However, most of the picornaviruses which affect humans have not been combated through vaccines. In particular, those which cause digestive and respiratory tract illnesses (e.g. the cold and stomach flu, which is separate from the more serious disease caused by influenza viruses) are both so numerous and so comparatively harmless that no vaccines have yet been developed to counter them.
- Sources and More Information -
eMedicine Medscape. "Picornavirus - Overview."
University of Carolina School of Medicine. "Picornaviruses - Enteroviruses and General Features of Picornaviruses."