Genus Influenzavirus B

Type Species	Influenza B virus	(FLUBV)

Distinguishing Features

Member viruses of the genus Influenzavirus B all have 8 genome segments. As for members of the genus Influenzavirus A, hemagglutin and the neuraminidase receptor-destroying enzyme are different glycoproteins. The conserved end sequences of the viral RNAs of the influenzaviruses B are 5-AGUAG(A/U)AACAA . . . and 3-UCGUCUUCGC . . . Influenza B virus proteins have sizes similar to those for Influenza A virus. NB, the second product of Influenza B virus segment 6, has an Mr 11 10³ (glycosylated 18 10³).

Antigenic Properties

Antigenic variation within the HA and NA antigens of influenzaviruses B has also been analyzed in some detail. In contrast to influenzaviruses A, no distinct antigenic subtypes are recognized for Influenza virus B, however, viruses with antigenically and genetically distinguishable lineages of HA and NA (e.g., the B/Victoria/2/87-like and the B/Yamagata/16/88-like viruses) have been shown to co-circulate in humans for over a decade. Influenzaviruses B are designated by their serotype/site of origin/strain designation/and year of origin. Antibody to HA neutralizes infectivity.

Biological Properties

Influenzaviruses B have circulated continuously in humans since they were first isolated in 1940 and have caused recurrent epidemics of respiratory disease. Although antigenic change (antigenic drift) occurs more slowly among influenzaviruses B than influenzaviruses A, influenzaviruses B cause epidemics characterized by high attack rates in student populations every 3 to 5 years.

List of Species Demarcation Criteria in the Genus

No separate species are currently recognized in the genus Influenzavirus B. This genus is comprised of a cluster of strains that replicate as a continuous lineage and can reassort genetically with each other. Although considerable antigenic and sequence differences exist among viruses in this genus, these differences are not sufficient for designation of separate species.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus name, genome sequence accession numbers [ ], and assigned abbreviation ( ) are:

Species in the Genus

Influenza B virus B/Lee/40	[M20170, M20168, M20172, K00423, K01395, J0209, J02095, J02096]	(FLUBV)

Tentative Viruses in the Genus

None reported.