unambiguous identification of the species.

Before then, a more liberal naming system was in effect: a species name shall consist of as few words as practicable but must not consist only of a host name and the word virus. Numbers, letters, or combinations thereof may be used as species epithets where such numbers and letters are already widely used. However, newly designated serial numbers, letters or combinations thereof are not acceptable alone as species epithets. If a number or letter series is in existence