Picornaviridae family represents a large family of virus that causes infections in humans, primates and other mammals. Enteroviruses, polio virus, foot-and-mouth disease virus (the first animal virus to be discovered), hepatitis A virus (HAV) and rhinoviruses are some examples of viruses in the Picornaviridae family. With the exclusion of polio infection or poliomyelitis (caused by polio virus) which has been eradicated in some parts of the world (e.g. USA), Picornaviruses have a worldwide distribution. There are nine genera of viruses in the Picornaviridae family; and these include Aphthovirus, Cardiovirus, Enterovirus, Erbovirus, Hepatovirus, Kobuvirus, Parechovirus, Rhinovirus, And Teschovirus. Only five genera of Picornaviridae family including Enterovirus, Hepatovirus, Kobuvirus, Parechovirus and Rhinovirus contain Picornaviruses that cause infections in humans.
Enteroviruses and polio virus are in the genus Enterovirus; foot-and-mouth disease virus (which causes foot-and-mouth disease in animals) is in the Aphthovirus genera; HAV is found in the Hepatovirus genera and rhinoviruses are found in the genera Rhinovirus. The human rhinovirus is the causative agent of the majority of common cold in humans; and the disease is characterized by inflammation of the nasal cavity. Rhinoviruses are transmitted via the respiratory route or tract of infected persons. HAV found in the Hepatovirus genera is the causative agent of infectious hepatitis in humans; and HAV is transmitted via the feacal-oral route. Kobuvirus species which is transmitted via the feacal-oral route causes gastroenteritis in humans; and infection with the virus is common amongst people who eat raw sea foods such as oysters.
Viruses in the Picornaviridae family are non-enveloped viruses that posses a ss(+)RNA genome. They measure between 28-30 nm in diameter and this makes members of viruses in this family one of the smallest viruses in terms of the size of their virion. Picornaviruses are resistant to ether. Enteroviruses which include polio virus, Coxsackie A, Coxsackie B and echoviruses are the different serotypes that make up the Enterovirus genera. Enteroviruses are transient inhabitants of the GIT of humans and they cause mild gastrointestinal disease in infected individuals. Poliomyelitis or polio caused by polio virus is one of the most serious diseases caused by Enteroviruses. But the disease which is characterized by the deformity of the limbs of infected children has been contained in most parts of the world due to massive immunization programmes against the disease. Polio virus infects motor neurons of the spinal cord and other parts of the CNS, and this leads to flaccid paralysis. Enteroviruses are transmitted via the feacal-oral route.
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