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The genus is distinguished on the basis of genetic characters.
Unlike other picornaviruses, kobuvirus capsids show a distinctive surface morphology when observed by electron microscopy (Figure 1E.Picronaviridae). The crystal structure of Aichi virus A (AiV-A1) was recently resolved (Sabin et al., 2016)
Virions are stable at pH 3.5.
Genome (Yamashita et al., 1998, Yamashita et al., 2003, Smits et al., 2013, Reuter et al., 2008, Reuter et al., 2009, Otomaru et al., 2016, Pankovics et al., 2016): up to 8,280 nt (5′-UTR: up to 744 nt; ORF: 7,299–7,467 nt; 3′-UTR: 136–240 nt). The genome of Aichi virus (AiV-A) has a high G+C base composition (59%). The 3′-UTR differs in the three species: members of Aichivirus A have the longest 3′-UTR at 240 nt, however, the 3′-UTRs of bovine kobuvirus (BKV, Kobuvirus B) and porcine kobuvirus (PKV, Kobuvirus C) are shorter at 177 and 170 nt, respectively. In AiV-A1, there is a 5′-proximal stem-loop involved in RNA replication and encapsidation. The IRESs of members of the Aichivirus A and Aichivirus B species are of type V, however, those of Aichivirus C (PKV) possess a type IV IRES. The cre is located in the 2A gene region of rabbit kobuvirus but has not been identified in other kobuviruses.
The deduced polyprotein is of c. 2,432–2,488 amino acids. There is a leader polypeptide of unknown function, and distinctive length (170–195 aa). 1AB remains uncleaved; however, a myristoylation signal (GxxxT) is present at the amino terminus of the polypeptide. The 2A protein contains an H-Box/NC motif.
AiV-A1 grows in cell cultures (BSC-1, Vero). AiV-A1 is thought to be a cause of human gastroenteritis. Kobuviruses have been isolated from humans, cattle, sheep and pigs. Kobuvirus genomes have been detected in faeces of dogs, cats, mice, marmots, rats, ferrets, goats, rabbits, bats, birds and in sewage.
Twenty genetic types are distinguished by means of phylogenetic analysis (Aichivirus A: 10 types, Aichivirus B: 3 types, Aichivirus C: 2 types, Aichivirus D: 2 types, Aichivirus E: 1 type, Aichivirus F: 3 types).
Aichivirus and bovine kobuvirus have been distinguished by neutralization of infectivity and serological assays.
Aichivirus: from the Aichi prefecture in Japan
Kobuvirus: from Japanese kobu, 'knuckle, bump' (reference to surface structure of virus particle).
Members of a species of the genus Kobuvirus:
The divergence (number of differences per site between sequences) of members of different Kobuvirus species ranges from 0.37–0.60 for P1 and 0.21–0.48 for 3CD.
grey squirrel kobuvirus [grey squirrel/UK/2010]
Norway rat kobuvirus 2 [rat/NYC-D21a/USA/2013]
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