The first published edition of the Catalogue2 listed 23 antigenic groups based on demonstrated serologic relationships between member viruses and an ungrouped category for viruses which were serologically unique. In the second published edition,5 the list of antigenic groups had expanded to 47; and reference was made to the Bunyamwera Supergroup, which was created to recognize intergroup relationships indicated by low level but reproducible cross-reactions between some members of different groups.
At present, the registered viruses constitute 50 antigenic groups, including an “Unassigned” collection of viruses serologically placed within the Bunyamwera Supergroup but which cannot be assigned to any of the individual groups. There is also a category termed “Ungroup” viruses; each of the ungrouped viruses is unique and must wait the discovery of a serologically related virus to become recognized as a group member. With the registration of Olifantsvlei virus, the Olifantsvlei (OLI) antigenic group was constituted and placed within the Bunyamwera Supergroup (the other member of the OLI serogroup has been studied but has not yet been registered). The Colorado tick fever (CTF) group was constituted upon registration of Eyach virus and demonstration of its relationship to Colorado tick fever virus. The Nairobi sheep disease (NSD) antigenic group was formed and (by priority) replaced the Ganjam serogroup upon demonstration of a close antigenic relationship of Nairobi sheep disease virus to Ganjam virus. The Marburg (MBG) antigenic group comprises Marburg virus plus the related, recently registered Ebola virus.