Most human viruses only infect humans. A viral particle. RNA or DNA that is coated with protein, and with or without a lipid envelope. The envelope is derived from host lipid bilayers. The envelope usually contains spikes, glycoproteins that project from the surface of the envelope.
Spikes function in attachment and entry to host cells.
Made up of a protein, without nucleic acid. Prions cause mad cow disease, Scrapie, Creutsfeld-Jakob disease, and Kuru. Icosahedral viruses have cubical symmetry. For example, poliovirus Enveloped icosahedral viruses. For example, herpes simplex virus Enveloped helical viruses.