TEM micrograph of<unk> virus<unk> myelitis is caused by infection with a member of the genus Enterovirus known as<unk> virus (PV). This group of RNA viruses colonize the gastrointestinal tract – specifically the oropharynx and the intestine. The incubation time (form the first signs and symptoms) ranges from three to 35 days, with a more common span of six to 20 days. PV infects and causes disease in humans alone. Its structure is quite simple, composed of a single (+) sense RNA genome enclosed in a protein shell called a capsid. In addition to protecting the virus' genetic material, the capsid proteins enable<unk> virus to infect certain types of cells. Three serotypes of<unk> virus have been identified –<unk> virus type 1 (PV1), type 2 (PV2), and type 3 (PV3) – each with a slightly different capsid protein. All three are extremely virulent and produce the same disease symptoms. PV1 is the most commonly encountered form, and the one most closely associated with paralysis. Individuals who are exposed to the virus, either through infection or by immunization via<unk>  vaccine, develop immunity. In immune individuals, IgA antibodies against<unk> virus are present in the tonsils and gastrointestinal tract and able to block virus replication; IgG and IgM antibodies against PV can prevent the spread of the virus to motor neurons of the central nervous system. Infection or vaccination with one serotype of<unk> virus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype. A rare condition with a similar presentation, nonpoliovirus<unk> myelitis, may result from infections with nonpoliovirus enteroviruses. Transmission<unk> myelitis is highly contagious via the fecal–oral (intestinal source) and the oral–oral (oropharyngeal source) routes. In endemic areas, wild<unk> viruses can infect virtually the entire human population. It is seasonal in temperate climates, with peak transmission occurring in summer and autumn. These seasonal differences are far less pronounced in tropical areas. The time between first exposure and first symptoms, known as the incubation period, is usually 6 to 20 days, with a maximum range of 3 to 35 days. Virus particles are excreted in the feces for several weeks following initial infection. The disease is transmitted primarily via the fecal–oral route, by ingesting contaminated food or water. It is occasionally transmitted via the oral–oral route, a mode especially visible in areas with good sanitation and hygiene.<unk>  is most infectious between 7 and 10 days before and after the appearance of symptoms, but transmission is possible as long as the virus remains in the saliva or feces. Factors that increase the risk of<unk>  infection or affect the severity of the disease include immune deficiency, malnutrition, physical activity immediately following the onset of paralysis, skeletal muscle injury due to injection of vaccines or therapeutic agents, and pregnancy. Although the virus can cross the maternal-fetal barrier during pregnancy, the fetus does not appear to be affected by either maternal infection or<unk>  vaccination. Maternal antibodies also cross the placenta, providing passive immunity that protects the infant from<unk>  infection during the first few months of life.
Polio
Sequela
Rubella
Typhidot
Smallpox
Mumps
Tongue disease
Cowpox