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Avian encephalomyelitis virus (AEV) is most similar to hepatitis A virus (genus Hepatovirus), but differs by possessing i) a type IV IRES (HAV is type III), ii) 2A with a H-box/NC motif and iii) 2B and 3A polypeptides with little sequence identity to the HAV counterparts.
No surface morphology is visible by EM.
AEV is stable at pH 3.0 and has a buoyant density of 1.31 to 1.33 g cm-3.
Length of genome (Marvil et al., 1999): c. 7,032 nt (5'-UTR: 494 nt; ORF: 6,405; 3'-UTR: 135 nt). There is little similarity between the genome sequences of tremoviruses and those of other picornaviruses. The 5′-UTR contains a 5′-terminal hairpin, two putative pseudoknots, and a short (ca. 40 nt) pyrimidine-rich (i.e. not pure poly-C) tract upstream of the type IV IRES. Nucleotide sequence identity between different strains is generally greater than 80%. AEV RNA contains the shortest of all picornavirus 5′-UTRs. The location of the cre is thought to possibly lie within the 3D region.
Similar to hepatoviruses, protein 1A of AEV is predicted to be extremely small, does not appear to be myristoylated at its N-terminus, and therefore may not be a component of the mature virus particle.
The polyprotein has a length of 2,134 aa and contains only a single proteinase (3Cpro). There is no L protein. The 2A protein has a H-box/NC motif. The primary cleavage of the polyprotein is predicted to occur at the 2A/2B junction, and is probably catalyzed by 3Cpro. Like hepatoviruses, the 1D/2A cleavage may be directed by an unknown cellular protease, or the VP1 protein may be subject to C-terminal trimming as in cardioviruses. The IRES is type IV.
Only a single serotype, avian encephalomyelitis virus 1 (AEV-1), has been recognized.
AEV causes encephalomyelitis in young chickens, pheasants, quail and turkeys. It can be transmitted both vertically and by the faecal-oral route; field strains are enterotropic. A live, highly enterotropic AEV vaccine is widely used to control the disease.
Tremo: from an alternative name for avian encephalomyelitis, epidemic tremor.
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