Poliovirus, the causative agent of poliomyelitis and a member of the family of Picornaviridae, is a human enterovirus. It is composed of an RNA genome that is a single-stranded positive-sense RNA. It was first isolate in 1909 and was published in 1981. It is one of the most well characterized viruses and has become a useful model system for understanding the biology of RNA viruses.
It infects human cells by binding to an immunoglobulin-like receptor on the cell surface. The three serotypes are PV1, PV2, and PV3. Each has a different capsid protein which defines cellular receptor specificity and virus antigenicity. PV1 is the most common form encountered in nature; however, all three forms are very infectious. Wild polioviruses can be found in approximately 10 countries and PV1 is highly localized in India, Pakistan, Afghanistan, and Egypt. Type 2 has been eradicated. Wild PV3 is only found in about five countries.
Each serotype is used to prepare vaccines against polio. Oral polio vaccine contains live attenuated strains of the three serotypes of poliovirus. They were formerly classified as a distinct species belonging to the genus Enterovirus in the family Picornaviridae. In 2008 the Poliovirus species was removed from the genus Enterovirus and the three serotypes were assigned to the species Human Enterovirus C.
The determinant of infection for any virus is its ability to enter a cell and produce additional infectious particles. Poliovirus is strictly a human pathogen and doesn’t naturally infect any other species. Infection occurs through the fecal-oral route. A person ingests the virus and replication occurs in the alimentary tract. The virus is then shed in the feces. This replication causes secondary viremia and leads to the development of minor symptoms such as fever, headache and sore throat. Paralytic disease can occur when the virus enters the central nervous system and replicates in motor neurons within the spiral cord, brain stem, or motor cortex, resulting in the selective destruction of motor neurons leading to paralysis.
Poliovirus evades the immune system by being able to survive highly acidic conditions and because it can replicate very quickly overwhelming host organs before an immune response happens. Anyone exposed to polio develops immunity to it. However, infection of one serotype does not provide immunity against others. Humans are the only known natural hosts of poliovirus although monkeys have been infected in experiments.
In 2002 researchers created the first synthetic virus by synthesizing poliovirus from its chemical code.