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Viruses assigned to the genus Almendravirus form a distinct monophyletic group based on well-supported Maximum Likelihood trees inferred from complete L sequences. Almendraviruses are capable of replication in mosquito cells in vitro but appear to be unable to replicate in vertebrates and so may infect only mosquitoes. The genome organisation features a gene encoding a small class 1a viroporin-like protein between the G gene and L gene.
In ultra-thin sections of infected insect cells, bullet-shaped virions (130–460 nm x 40–55 nm) have been reported but these may include defective-interfering particles and longitudinally fused virions (Vasilakis et al., 2014, Contreras et al., 2017).
Almendravirus genomes consist of a single molecule of negative-sense, single-stranded RNA and range from approximately 10.9–11.9 kb (Vasilakis et al., 2014, Contreras et al., 2017).
The N, P, M, G and L share sequence homology and/or structural characteristics with the cognate proteins of other rhabdoviruses. The small class 1a viroporin-like proteins encoded in the U1 gene range from 51 to 80 amino acids (6.1–9.5 kDa) and feature a very short N-terminal domain, a predicted hydrophobic transmembrane domain and a C-terminal domain that is rich in basic residues (Vasilakis et al., 2014, Contreras et al., 2017).
Almendravirus genomes include five genes (N, P, M, G and L) encoding the structural proteins and an additional gene between the G and L genes encoding a class 1a viroporin-like protein (U1) (Vasilakis et al., 2014, Contreras et al., 2017). In the Balsa virus (BALV) genome, there is an alternative ORF (Px) within the P gene. All other almendravirus ORFs occur in discrete transcriptional units including conserved transcription initiation and transcription termination/polyadenylation sequences (Figure 1.Almendravirus).
Figure 1.Almendravirus. Schematic representation of almendravirus genome organisations. N, P, M, G and L represent ORFs encoding the structural proteins. The U1 ORFs (yellow) each encode class 1a viroporin-like proteins.
Each of the viruses assigned to the genus was isolated from mosquitoes in the Americas. The viruses replicate in mosquito cell lines but failed to replicate in vertebrate (mammal, bird or reptile) cell cultures or in suckling mice. They have been isolated from Culex, Aedes, Anopheles and Psorophora mosquitoes and may be mosquito-specific viruses. The known distribution of members of the genus includes Peru, Panama, Colombia and Florida (Vasilakis et al., 2014, Contreras et al., 2017).
Viruses assigned to different species within the genus Almendravirus have several of the following characteristics: A) minimum amino acid sequence divergence of 5% in N; B) minimum sequence divergence of 10% in L; C) minimum amino acid sequence divergence of 15% in G; D) significant differences in genome organisation as evidenced by numbers and locations of ORFs; E) can be distinguished in virus neutralisation tests; and F) occupy different ecological niches as evidenced by differences in hosts and/or arthropod vectors. All viruses currently assigned to the genus meet criteria A, B, C and F.
The genus name is derived from the name of the virus assigned to the type species (Puerto Almendras virus; PTAMV; species Puerto Almendras almendravirus).
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