ABSTRACT
Viruses are classified according to several criteria (Table 3.1), including the type of nucleic acid in the genome (DNA or RNA); whether the genome is linear, circular or segmented; the polarity of the genome (positive or negative); the morphology of the capsid (icosahedral, helical or complex); and whether an envelope is present. Moreover, strains within a given species can be discriminated according to the specificity of antibodies. If a particular antibody is neutralizing, all strains recognized by it are termed a serotype.
