Color enhanced Transmission Electron Micrograph (TEM) of a cluster of polio virus particles (Mohoney type 1). Each particle is composed of a protein coat (capsid) around a core containing RNA genetic material, and is only 27 nanometers across. Poliovirus, the causative agent of poliomyelitis (commonly known as polio), is a human enterovirus and member of the family of Picornaviridae. Poliovirus is composed of an RNA genome and a protein capsid. Poliovirus is a positive-stranded RNA virus. Poliovirus is structurally similar to other human enteroviruses (coxsackieviruses, echoviruses, and rhinoviruses), which also use immunoglobulin-like molecules to recognize and enter host cells. Poliovirus was first isolated in 1909 by Karl Landsteiner and Erwin Popper. In 1981, the poliovirus genome was published by two different teams of researchers. Because of its short genome and its simple composition, only RNA and a nonenveloped icosahedral protein coat that encapsulates it, poliovirus is widely regarded as the simplest significant virus. Poliovirus is one of the most well-characterized viruses, and has become a useful model system for understanding the biology of RNA viruses. Magnification: 65,000x.