Composite image showing illustration of polio virus capsids against a transmission electron micrograph (TEM) of polio virus particles. Poliovirus particles (virions) are composed of an outer protein coat (capsid) encasing RNA (ribonucleic acid), the genetic material of the virus. Polio virus causes poliomyelitis, a disease that destroys motor neurons (nerve cells) which control muscles for swallowing, circulation, breathing, and limb movement.