ICTV Report

Family: Nairoviridae

Genus: Norwavirus

 

Distinguishing features

Běijí nairovirus (BJNV; discouraged synonym: Gakugsa virus [unpublished]) and Grotenhout virus (GRHV; discouraged synonyms: Norway nairovirus 1 and Pustyn virus [unpublished])) are the only classified norwaviruses. Both infect ixodid ticks. Notably, norwaviruses have bisegmented genomes (Pettersson et al., 2017, Vanmechelen et al., 2017, Meng et al., 2019, Luo et al., 2021, Wang et al., 2021, Liu et al., 2022, Cai et al., 2023, Wang et al., 2023a).

Virion

Virions are spherical and enveloped with a diameter of approximately 90-100 nm (Wang et al., 2021).

Nucleic acid

Norwaviruses have bisegmented negative-sense RNA genomes of 18.6 kb (small [S] segment: 3.7 kb; large [L] segment: 14.9 kb) (Pettersson et al., 2017, Vanmechelen et al., 2017, Meng et al., 2019, Luo et al., 2021, Wang et al., 2021, Liu et al., 2022, Cai et al., 2023, Wang et al., 2023a).

Proteins

Based on sequence data only, norwaviruses likely express two structural proteins: nucleoprotein (N) and large protein (L) (Pettersson et al., 2017, Vanmechelen et al., 2017, Meng et al., 2019, Luo et al., 2021, Wang et al., 2021, Liu et al., 2022, Cai et al., 2023, Wang et al., 2023a).

Genome organization and replication

The S segment encodes N and the L segment encodes L (Figure 1 Norwavirus). Norwavirus genomic segments are expected to assume circular forms via non-covalent binding of complementary and conserved 3′ and 5′ terminal sequences.

Norwavirus genome
Figure 1 Norwavirus. Schematic representation of norwavirus genome organization. The 5′- and 3′-ends of each segment (S and L) are, by analogy to other nairovirids, predicted to be complementary at their termini, likely promoting the formation of circular ribonucleoprotein complexes within the virion.

Biology

BJNV infects taiga ticks (ixodid Ixodes persulcatus (Schulze, 1930)) in China and Russia and is associated with human febrile illness in northeastern China. Human BJNV isolates replicate in suckling mice but are not lethal (Meng et al., 2019, Wang et al., 2021, Liu et al., 2022, Cai et al., 2023, Wang et al., 2023a). GRHV infects castor bean ticks (ixodid Ixodes ricinus (Linnaeus, 1758)) in Belgium, China, and Russia (Vanmechelen et al., 2017, Luo et al., 2021).

Species demarcation criteria

Members of different species in the genus are <93% identical in the L amino-acid sequence.