Relation of stage of illness to presence of virus in test material &s to appearance of specific antibody Stage or period Virus Specific of illness detectable antibody Incubation R arely No Prodrome Occasionally No Onset Frequently Occasionally Acute pl ase Frequently Frequently Recovery Rare Usually Convalescence ry rarely suallyRelation of stage of illness to presence of virus in test material & to appearance of specific antibody Stage or period of illness Virus detectable Specific antibody Incubation Rarely No Prodrome Occasionally No Onset Frequently Occasionally Acute phase Frequently Frequently Recovery Rarely Usually Convalescence Very rarely Usually