Viruses are microorganisms, which are tiny organisms that are difficult for individuals to observe with the naked eye, and should belong to species in the larger category of organisms, other microorganisms include bacteria, mycoplasma, chlamydia, rickettsia, fungi, actinomycetes, and spirochetes. Viruses are non-cellular organisms that are tiny, simple in structure and contain only one nucleic acid and must parasitize and proliferate by replication in living cells. Viruses are non-cellular life forms, consisting of a long chain of nucleic acids and a protein shell, and have no metabolic mechanism or enzyme system of their own, so they are chemical substances that have no life activity and cannot reproduce themselves independently when they leave the host cell.