Family: Picornaviridae
Genus: Megrivirus
Distinguishing features
The genus is distinguished on the basis of genetic characters.
Virion
Morphology
No details are available on the morphology of virions.
Nucleic acid
Genome (Honkavuori et al., 2011, Phan et al., 2013, Lau et al., 2014, Boros et al., 2014b, Liao et al., 2014, Kim et al., 2015, Boros et al., 2017, Wang et al., 2017, Yinda et al., 2019): 8,541–10,101 nt (5′-UTR: >461–833 nt; ORF: 7,455–8,916 nt; 3′-UTR: 175–671 nt). The 5′-UTR contains a type IV-B IRES with the exception of harrier megrivirus which has a type II IRES; the 3′-UTR is exceptionally long. The location of the cre has not been identified.
Genome organization and replication
Genome layout:
VPg+5′-UTRIRES - [(L-)1AB-1C-1D/(2A1-2A2-2A3-)2A4H-box/NC-2B-2C/3A-3B-3C-3D]-3′-UTR-poly(A)
The deduced polyprotein ranges from 2,485 to 2,972 aa. Only members of Megrivirus E have an L protein of unknown function. 1AB remains uncleaved and has an N-terminal myristoylation signal. There are 1–4 2A proteins, the last of which exhibiting an H-box/NC motif. A second ORF has been proposed at the 3′-end of the genome but not yet demonstrated. Sequence data indicate interspecies recombination in the evolution of megriviruses (Lau et al., 2014, Boros et al., 2014b).
Biology
The virus is suspected to be the etiological agent of turkey viral hepatitis (Honkavuori et al., 2011, Tzianabos and Snoeyenbos 1965). The natural host is poultry (turkey and chicken). No virus has been isolated. Viral RNA was detected in liver, bile, intestine, serum and cloacal swabs of turkeys suffering from turkey viral hepatitis; RNAs of related viruses have been detected in chickens, ducks, feral pigeons, harriers and penguins.
At least 10 types are distinguished by means of phylogenetic analysis (Megrivirus A: 2 types, Megrivirus B: 2 types, Megrivirus C: 2 types, Megrivirus D: 1 type, Megrivirus E: 1 type; natural interspecies recombinants: MeV-B3CP-APol, MeV-A1CP-CPol).
Derivation of names
Megrivirus: from the host (turkey) genus name Meleagris
Species demarcation criteria
Members of a species of the genus Megrivirus:
- are less than 55% divergent in P1 aa sequence
- are less than 40% divergent in 2C + 3CD aa sequence
- share an essentially identical genome organization
The divergence (number of differences per site between sequences) of members of different Megrivirus species ranges from 0.52–0.67 for P1 and 0.31–0.53 for 3CD. Megrivirus taxonomy is complicated by apparent interspecies recombination events in the evolution of viruses belonging to the species Megrivirus A and Megrivirus C.