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Polio virus.
Poliomyelitis ("polio") is a viral paralytic disease. The causative agent, a virus called poliovirus, enters the body orally, infecting the intestinal lining. It may proceed to the blood stream and into the central nervous system causing paralysis and muscle weakness.

There are effective vaccines against polio, and since their introduction, the disease has been wiped out in the Americas. The first mass vaccination of children against polio began in Pittsburgh, Pennsylvania on February 23, 1954. The World Health Organization is working to eliminate polio worldwide.

People who have survived polio sometimes develop additional symptoms, notably muscle weakness, decades later; these symptoms are called post-polio syndrome.

The first medical report on poliomyelitis was by Jakob Heine in 1840. Karl Oskar Medin was the first to empirically study a poliomyelitis epidemic in 1890. The work of these two physicians has led to the disease being known as the Heine-Medin disease.

Polio victims

Synthetical polio viruses

In 2002, US microbiologists managed to fully synthesise polio viruses without using any part of natural polio viruses except for their (immaterial) genetic information in the form of DNA, which was replicated and converted to the RNA found in natural polio viruses. The RNA fragments were then put into a special "cell-free juice", which consists of human cells that had their membranes and structural compounds removed, which started the virus assembly mechanism. The synthetical viruses were able to infect, paralyse and kill a breed of laboratory mice. There are concerns that states (in particular "rogue states") or terrorist organisations may synthesise lethal viruses in a similar way, and use them for extortion or bioterrorism.