Distinguishing features

Huángjiāo virus (HUJV) is the only classified thamnovirus. Like striaviruses, but unlike cuevaviruses, dianloviruses, ebolaviruses, and marburgviruses, thamnoviruses apparently infect fish (Shi et al., 2018). Notably, thamnovirus genomes encode at least one protein without obvious homologs in other filovirus genera and do not encode matrix protein (VP40) or ribonucleoprotein (RNP) complex-associated protein (VP24). 

Virion

Morphology

Not reported.

Physicochemical and physical properties

Not reported.

Nucleic acid

Virions are assumed to contain one or several copies of linear negative-sense RNA genomes that are encapsidated independently.

Proteins

Thamnoviruses likely express at least six proteins, of which at least four (nucleoprotein [NP], polymerase cofactor [VP35], glycoprotein [GP_1,2], and large protein [L]) are homologs of proteins expressed by other filoviruses. The second most abundant structural protein in a thamnovirion is assumed to be NP, which encapsidates the striavirus genome. The least abundant protein is assumed to be L, which mediates thamnovirus genome replication and transcription (Shi et al., 2018).

Lipids

Not reported.

Carbohydrates

Not reported.

Genome organization and replication

The thamnovirus genome has the gene order 3′- U1-NP-VP35-GP-VP30-L-5′, with U denoting genes expressing proteins of unknown function (Figure 1.Thamnovirus). The undetermined extragenic sequences at the extreme 3′-end (leader) and 5′-end (trailer) of the genome are assumed to be conserved and partially complementary. The transcriptional initiation and termination (polyadenylation) sites have yet to be identified. 

Figure 1.Thamnovirus. Schematic representation of the thamnovirus genome organization. Genome is drawn to scale. Courtesy of Jiro Wada, NIH/NIAID/DCR/IRF-Frederick, Fort Detrick, MD, USA.

 The replication strategy of thamnoviruses remains to be studied.  

Biology

Thamnoviruses were discovered in 2011 by high-throughput sequencing of samples taken from greenfin horse-faced filefish (Thamnaconus septentrionalis (Günther, 1874)), captured by fishing trawlers in the East China Sea (Shi et al., 2018).

Antigenicity

Not reported.

Derivation of names

Thamnovirus: from Thamnaconus septentrionalis, the fish species to which the presumed host of HUJV, greenfin horse-faced filefish, has been assigned (Shi et al., 2018).

Species demarcation criteria

The genus currently includes only a single species.

Member species

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

Related, unclassified viruses 

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