Pathology is the study of the causes and effects of disease or injury. The word pathology also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices.

Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. In about 0.5 percent of cases, it moves from the gut to affect the central nervous system and there is muscle weakness resulting in a flaccid paralysis.

Prevalence is the proportion of a population who have a specific characteristic, for example a disease, in a given time period.