Herbeviruses were originally isolated from Culex mosquitoes in Africa. Unlike most viruses of other genera in the family Peribunyaviridae, herbeviruses do not encode any non-structural proteins, and possess a 500 nt insertion in the RNA-directed RNA polymerase/endonuclease (L) protein ORF and a truncated glycoprotein ORF (Marklewitz et al., 2013). Data from in vitro analyses indicate that herbeviruses are not able to infect vertebrates and so they are considered to be arthropod-specific viruses (Marklewitz et al., 2013).
Mature virions are spherical, enveloped, of 90−110 nm in diameter (Marklewitz et al., 2013).
Herbeviruses have the peribunyavirus-typical tripartite, negative-sense genome. The terminal ends have a conserved seven nucleotide sequence (coding sense) 5′-AGTAGTG…CACTACT-3′, whereas the remaining non-coding region is highly variable in sequence and length (Marklewitz et al., 2013). Similar to orthobunyaviruses, viral mRNA is 5′-capped via cap snatching from host mRNAs and is truncated relative to the vRNA (Marklewitz et al., 2013).
Herbevirus genomes encode four structural proteins: L, the glycoproteins Gn and Gc, and the nucleocapsid protein N (Table 2.Peribunyaviridae). These viruses do not encode any non-structural proteins (Marklewitz et al., 2013) (Figure 1.Herbevirus).
Virion lipids are derived from host membranes (Marklewitz et al., 2013).
The Gn and Gc proteins contain N-linked glycosylation sites and are likely to be modified by N-glycosylation (Marklewitz et al., 2013).
Genome organization and replication
Herbevirus S segments encode a nucleocapsid protein (N) of 225−226 amino acids. Their M segments of 2683–3118 nt are about 1200 nt shorter than the typical orthobunyavirus M segment, corresponding to a 482 amino acid truncation at the N-terminus of the Gc protein. Regions coding for the non-structural protein NSm of other peribunyaviruses have not been described. The L segments are about 500 nt longer than the L segments of orthobunyaviruses and contain a unique conserved region of unknown function upstream of the RdRP motifs (Marklewitz et al., 2013).
Figure 1.Herbevirus. Herbevirus coding strategy. vcRNAs are depicted in 3′→5′ direction and mRNAs are depicted in a 5′→3′ direction. Coloured boxes on the mRNAs depict ORFs that encode the N, nucleocapsid protein; Gn and Gc, external glycoproteins; L, large protein.
Replication of genomes, morphogenesis in the Golgi complex, and virus secretion at the cellular membranes are similar to those of other peribunyaviruses (see ‘Genome organisation and replication’ on the family page).
Herbeviruses were originally isolated from Culex mosquitos in Côte d’Ivoire, Ghana, and Uganda. A vertebrate host has not been identified, and in vitro studies have shown restricted growth in cell culture above 31°C (Marklewitz et al., 2015), suggesting that these viruses are restricted to mosquitoes (Marklewitz et al., 2013).
Species demarcation criteria
Species within the genus Herbevirus can be defined by (Junglen et al., 2016):
- the approximately 1 kb sequence fragment containing the core polymerase domain (premotif A to motif E) of the third conserved region of the L protein being less than 90% identical at the amino acid level compared to that of any other described herbevirus.