Family Paramyxoviridae, Genus Morbillivirus. The same genus contains the viruses of Canine Distemper and Bovine Rinderpest.
Man is the only known reservoir.
New world monkeys are more resistant than old world monkeys but exhibit high mortality when infected. Virus is excreted from the mucous membranes of the eye and pharynx and later from the respiratory and urinary tracts. Virus is shed in the prodromal phase and continues through the exanthematous phase. Can spread from man to monkey, monkey to monkey, man to man, and back to monkey to man. Many infections occur subclinically.