Polio, or poliomyelitis, is a highly contagious viral infection that can lead to paralysis, breathing problems, or even death. The term poliomyelitis is from the Greek polios poliÃ³s meaning, grey myelos myelÃ³s referencing the, spinal-cord and itis. Meaning inflammation polio can be classified as either symptomatic. or asymptomatic
1 Prions are proteins that can force conformational changes in natural proteins and seem to cause disease (kuru, new variant Creutzfeldt-Jakob disease, and fatal familial insomnia).  A virus is an obligate intracellular pathogen (meaning that it must live within the cells of its host in order to reproduce).
Facultative means optional or discretionary (antonym obligate), used mainly in biology in phrases such as: 1  Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production. It can survive in either environment. Facultative biped, an animal that is capable of walking or running on two legs as well as walking or running on four limbs or more, as appropriate.