The causative agent of Poliomyelitis is a virus.
Poliomyelitis, also known as polio, is an infectious disease caused by a virus called the poliovirus. This virus primarily affects the nervous system and can lead to paralysis, muscle weakness, and even death. The virus is spread from person to person, usually through contaminated food or water.
The other options, Fungus, Protozoan, and Bacterium, are not the cause of Poliomyelitis.