Polio, also called poliomyelitis, is a highly contagious viral disease that was virtually eradicated in the latter half of the last century in large part due to strong support of research by its most notable victim, President Franklin Delano Roosevelt.
Humans are the only known natural hosts for poliovirus, which enters the body when fecal matter carrying the virus is ingested, usually through contaminated drinking water or through hand-to-mouth contact when people fail to wash their hands properly. The virus then multiplies in the intestine over a 6-20 day period before symptoms appear.
Approximately, 95% of people infected with polio do not show any symptoms of the disease, but can still spread it. The 4-8% of polio infections that do result in illnesses can produce a range of symptoms from stiffness, dizziness, and headaches to paralysis. Nonparalytic polio occurs in 1-2% of infections, with patients usually recovering fully in about a week. Paralytic polio, the most severe and infamous form of the disease occurs in less than 1% of all infections and only one in 200 of those lead to irreversible paralysis (usually in the legs). About 5%-10% of those who contract paralytic polio die of respiratory paralysis.
Poliovirus is a member of the Picornaviridae family of RNA viruses. It is a simple virus whose genome is a single-stranded RNA molecule of approximately 7500 nucleotides. There are three immunologically distinct serotypes to make the single stranded RNA of poliovirus, all of which are capable of causing disease.