Family: Pneumoviridae

Genus: Orthopneumovirus

Distinguishing features

Members of the genus Orthopneumovirus possess 10 genes including two NS1 and NS2 which are promoter proximal (i.e. before) the N gene. The gene order is NS1-NS2-N-P-M-SH-G-F-M2-L. Alignments of the L proteins show moderate conservation of the sequences between the human, murine, bovine and ovine viruses. Their genome length is larger than that of the members of the other genus. 

Virion

See discussion under family description. 

Genome organization and replication

See discussion under family description. 

Biology

See discussion under family description. 

Species demarcation criteria

HRSV and MPV are distinguished by host range (humans versus mice) and a lack of cross-neutralization. Amino acid sequence relatedness between these two viruses varies from undetectable to intermediate, depending on the protein (for example, the NS1 and NS2 proteins lack demonstrable relatedness, whereas the N and F proteins share 60% and 40% amino acid identity, respectively). Their gene organization differs only in that MPV lacks the M2/L gene overlap and has an additional ORF in the P mRNA. BRSV differs from HRSV in host range, specifically cattle versus humans. The two viruses share considerable sequence and antigenic relatedness, but also can clearly be distinguished on either basis. For example, the N and F proteins have 81% amino acid sequence identity between BRSV and HRSV, compared to 96% and 89%, respectively, between the two HRSV subgroups. The G attachment protein has only 21-29% and 30% amino acid sequence identity between HRSV versus ovine isolates  and BRSV, respectively, compared to 53% identity between the HRSV subgroups.  Antisera against BRSV or HRSV will cross-neutralize each other with a 6- to 64-fold reduction in efficiency. 

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations. 

Caprine and ovine RSV strains have been described. Caprine RSV appears to be closely related to BRSV, and ovine RSV and BRSV appear to represent two subgroups of ungulate RSV, similar to the two subgroups of HRSV. A virus called canine pneumovirus has been isolated from dogs with respiratory disease, but complete genome sequence analysis indicates that it is very highly related to MPV (95-96% nucleotide sequence identity) (Renshaw et al., 2011). A survey of specimens from bats worldwide by RT-PCR and sequence analysis provided preliminary evidence of possible additional species of orthopneumovirus, but this remains to be substantiated (Drexler et al., 2012).