Measles is caused by a ssRNA virus belonging to the Paramyxoviridae ... This is followed by the acute onset of a rosey pink, nonpruritic macular rash, predominantly on the neck and trunk.

Blood tests for hepatitis A virus IgM, hepatitis B virus core IgM ... The patient’s fever and diffuse macular rash are consistent with secondary syphilis, and his arthritis most likely reflects ...

An exanthem is any eruptive skin rash that may be associated with fever ... exanthems are most often related to infection and, of these, viral infections are the most common.