Distinguishing features

Měnglà virus (MLAV) is the only currently classified dianlovirus. Like cuevaviruses, marburgviruses, and possibly ebolaviruses, but unlike striaviruses and thamnoviruses, dianloviruses infect bats. Dianlovirus genomes are highly reminiscent in organization of marburgvirus genomes but contain four rather than only one gene overlap (Yang et al., 2019).

Virion

Morphology

Not reported.

Physicochemical and physical properties

Not reported.

Nucleic acid

Dianlovirus genomes are linear non-segmented RNA molecules of negative polarity. The genomes are about 18.5 kb (Yang et al., 2019). Genomic RNA is likely uncapped and not polyadenylated. 

Proteins

Dianloviruses express seven structural proteins, all of which are homologous to those of cuevaviruses, ebolaviruses, and marburgviruses (Table 1.Dianlovirus). The second most abundant structural protein in virions is assumed to be the nucleoprotein (NP), which encapsidates the dianlovirus genome. The least abundant protein is assumed to be the large protein (L), which mediates dianlovirus genome replication and transcription via its RNA-directed RNA polymerase (RdRP) domain. The dianlovirus ribonucleoprotein (RNP) complex likely consists of NP, RNP complex-associated protein (VP24), polymerase cofactor (VP35), transcriptional activator (VP30), and L. These RNP complexes associate with the matrix protein (VP40), which lines the inner side of the virion membrane and GP_1,2, which form globular spikes on the outside of the virion membrane (Yang et al., 2019).

Table 1.Dianlovirus. Location and functions of dianlovirus structural proteins.

IFNA1, interferon alpha 1; IFNB1, interferon beta 1; NEDD4, NEDD4 E3 ubiquitin protein ligase; NPC1, NPC intracellular cholesterol transporter 1; PRKRA, protein activator of interferon induced protein kinase EIF2AK2; RNP, ribonucleoprotein; STAT1, signal transducer and activator of transcription 1; TSG101, tumor susceptibility 101; VP, virus protein

Lipids

Not reported.

Carbohydrates

Not reported. 

Genome organization and replication

The dianlovirus genome has the gene order 3′-NP-VP35-VP40-GP-VP30-VP24-L-5′ (Figure 1.Dianlovirus). The undetermined extragenic sequences at the extreme 3′-end (leader) and 5′‑end (trailer) of the genome are assumed to be conserved and to be partially complementary. Genes are flanked by conserved transcriptional initiation and termination (polyadenylation) sites. Four dianlovirus genes overlap (Yang et al., 2019). 

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

The replication strategy of dianloviruses remains to be studied but is assumed to be highly similar to that of marburgviruses and reminiscent of that of cuevaviruses and ebolaviruses. Dianlovirions are assumed to associate with attachment factors at the plasma membrane that mediate infection by endocytosis. Dianlovirus GP_1,2 mediates cell surface C-type lectin binding and subsequent low-pH-dependent fusion into endosomes, followed by GP_1,2 binding to the endosomal receptor NPC intracellular cholesterol transporter 1 (NPC1), which is also used by cuevaviruses, ebolaviruses, and marburgviruses. Uncoating is presumed to occur in a manner analogous to that of other mononegaviruses. Dianlovirus transcription and genome replication likely take place in the cytoplasm and, in general, follow the models for members of the families Paramyxoviridae and Pneumoviridae. Transcription starts at the conserved transcriptional initiation site, and polyadenylation occurs at a stretch of uridine residues within the transcriptional termination site. The 5′-terminal non-coding sequences favor hairpin‑like structures for all mRNAs. Replication involves the synthesis of full-length positive-sense copies (antigenomes). During infection, it is assumed that massive amounts of nucleocapsids accumulate intracellularly and form intracytoplasmic inclusion bodies. Virions are likely released via budding from plasma membranes (Figure 3.Filoviridae) (Yang et al., 2019).

Biology

Dianloviruses were discovered in 2019 by high-throughput sequencing of samples taken from an apparently healthy Rousettus sp.) in China (Yang et al., 2019).

Antigenicity

Initial studies indicate that MLAV is antigenically distinct from other filoviruses, but more closely related to marburgviruses than to ebolaviruses (Sherwood and Hayhurst 2019).

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.

Derivation of names

Dianlovirus: from 滇 [diān], an abbreviation denoting China’s Yúnnán Province, and filovirus (Yang et al., 2017).

Related, unclassified viruses 

Virus names and virus abbreviations, are not official ICTV designations.