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 the 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al., 2015, Boros et al., 2017, Wang et al., 2017), (R. Zell, C.K. Yinda, J. Esefeld, H.U. Peter and J. Matthijnssens (unpublished)): 8,541–10,101 nt (5′-UTR: >461–833 nt; ORF: 7,455–8,916 nt; 3′-UTR: 175-671 nt). 5′-UTR contains a type IV-B IRES with exception of harrier megrivirus which has a type II IRES; 3′-UTR is exceptionally long. The location of the cre has not been identified. 

Genome organization and replication

Genome layout:

VPg+5′-UTRIRES-IVB- [(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 a L protein. 1AB remains uncleaved and has a N-terminal myristoylation signal. There are 1–4 2A proteins, the last of which exhibiting a H-box/NC motif. A second functional 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).

Antigenicity

See discussion under family description.

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). 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.

Species demarcation criteria

Members of a species of the genus Megrivirus share an essentially common 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 an apparent interspecies recombination event in the evolution of viruses belonging to the Megrivirus A and Megrivirus C species.

Sequence data of capsid protein-encoding gene regions indicate at least 10 types (Megrivirus A: 3 types, Megrivirus B: 2 types, Megrivirus C: 3 types, Megrivirus D: 1 type, Megrivirus E: 1 type).

Member species

SpeciesVirus name(s)Exemplar isolateExemplar accession numberExemplar RefSeq numberAvailable sequenceOther isolatesOther isolate accession numbersVirus abbreviationIsolate abbreviation
Megrivirus Amegrivirus A2; duck megrivirusLYKC663628NC_024120Complete genomeMeV-A2
Megrivirus Amegrivirus A3; goose megrivirus 1W18KY369299MeV-A3
Megrivirus Amegrivirus B3CP-APOL; goose megrivirus 2; recombinant virusHN56KY369300
Megrivirus Bpigeon mesivirus 1HK21KC876003NC_038957Complete coding genomeMeV-B1
Megrivirus Bmegrivirus B2; pigeon mesivirus 2pigeon/GALII5-PiMev/2011/HUNKC811837MeV-B2
Megrivirus Cchicken megriviruschicken/B21-CHV/2012/HUNKF961186NC_039235Complete genomeMeV-C1
Megrivirus Cmegrivirus C227CKF979336MeV-C2
Megrivirus Cmegrivirus A1CP-CPOL; turkey hepatitis virus; recombinant virus2993DHM751199
Megrivirus Dharrier megrivirusharrier/MR-01/HUN/2014KY488458NC_034617Complete genomeMeV-D
Megrivirus Epenguin megriviruspenguin/KGI-BHS-P5/2015MF405436NC_039004Complete genomeMeV-E

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

Derivation of names

Megri-: from the host (turkey) genus name Meleagris