Genus: Megrivirus


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 (Lau et al., 2014, Honkavuori et al., 2011, Boros et al., 2014b, Liao et al., 2014, Phan et al., 2013, 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.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Megrivirus Amegrivirus A2; duck megrivirusLYKC663628NC_024120Complete genomeMeV-A2
Megrivirus Amegrivirus A3; goose megrivirus 1W18KY369299Complete genomeMeV-A3
Megrivirus Amegrivirus B3CP-APOL; goose megrivirus 2; recombinant virusHN56KY369300Complete genome
Megrivirus Bmegrivirus B1; pigeon mesivirus 1HK21KC876003NC_038957Complete coding genomeMeV-B1
Megrivirus Bmegrivirus B2; pigeon mesivirus 2pigeon/GALII5-PiMev/2011/HUNKC811837Complete genomeMeV-B2
Megrivirus Cmegrivirus C1; chicken megriviruschicken/B21-CHV/2012/HUNKF961186NC_039235Complete genomeMeV-C1
Megrivirus Cmegrivirus C227CKF979336Complete genomeMeV-C2
Megrivirus Cmegrivirus C3RS/BR/2015/3RMG846465Complete genomeMeV-C3
Megrivirus Cmegrivirus A1CP-CPOL; turkey hepatitis virus; recombinant virus2993DHM751199Complete genome
Megrivirus Dmegrivirus D1; harrier megrivirusharrier/MR-01/HUN/2014KY488458NC_034617Complete genomeMeV-D
Megrivirus Emegrivirus E1; penguin megriviruspenguin/KGI-BHS-P5/2015MF405436NC_039004Complete genomeMeV-E

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.