From the Picornavirus Study Group
Taxanomic proposal no. 1

1. Proposal
To create a new genus, Parechovirus, within the family Picornaviridae

2. Purpose
Biological and sequence analysis has indicated that two species of picornavirus, human echovirus 22 and human echovirus 23, have a number of important features which differentiate them from all other picornaviruses studied to date. These viruses, which are currently classified, like the other echovirus serotypes, within the enterovirus genus, are highly divergent in sequence, no protein having a greater than 30% level of identity when compared with any other picornavirus. A further feature that distinguishes these viruses from all other picornaviruses is the apparent lack of cleavage in VP0, which, also unusually, is not myristoylated. The mature capsid therefore appears to comprise only three proteins, VP0, VP3 and VP1. Since, in all other respects, these viruses conform to the description of the Picornaviridae, it is proposed to move them from the enteroviruses to a new genus, Parechovirus, while retaining them within the family (with an appropriate amendment to the latter's description).

3. Revised organisation
The family would now consist of the following six genera:

• Enterovirus
• Rhinovirus
• Cardiovirus
• Aphthovirus
• Hepatovirus
• Parechovirus

4. Derivation of proposed name
Parechovirus, a contraction of Para-echovirus, recalls the former classification of the viruses as echoviruses, the "e" of "echo" alluding to the fact that these are enteric viruses, while the par(a) prefix conveys the fact that they belong to a lineage distinct from (or parallel with) that of the true echoviruses and other members of the enterovirus genus.

5. References

Hyypiä, T., Horsnell, C., Maaronen, M., Khan, M., Kalkkinen, N., Auvinen, P., Kinnunen, L. and Stanway, G. (1992). A distinct picornavirus group identified by sequence analysis. Proc. Natl. Acad. Sci., USA 89:8847-8851.

Stanway, G., Kalkkinen, N., Roivainen, M., Ghazi, F., Khan, M., Smyth, M., Meurman, O. and Hyypiä, T. (1994). Molecular and biological characteristics of echovirus 22, a representative of a new picornavirus group. J. Virol. 68:8232-8238.

• human parechovirus 1 (formerly human echovirus 22)
• human parechovirus 2 (formerly human echovirus 23)

4. Derivation of proposed name
As for proposal 1

5. References
As for proposal 1.

From the Picornavirus Study Group
Taxanomic proposal no. 3

1. Proposal
To transfer human Vilyuisk encephalomyelitis virus from the genus Enterovirus to the genus Cardiovirus

2. Purpose
Vilyuisk human encephalomyelitis virus (VHEV, often referred to simply as "Vilyuisk virus") is thought to be the cause of a neurodegenerative disease among the Yakuts people of Siberia. Isolated originally from the cerebrospinal fluid of one such patient, the virus has since been passed in the brains of mice. The virus is antigenically related to Theiler's murine encephalomyelitis virus (TMEV), a naturally occurring enteric picornavirus of mice, which was at one time classified as an enterovirus but is now assigned to the cardioviruses. The sequence of VHEV RNA confirms that the virus is related closely enough to TMEV to identify it as "a divergent Theiler's virus"¹, and hence to require transfer to the cardioviruses. The predicted sequence of the capsid protein precursor is 78% identical to that of TMEV². Like TMEV, it has no poly(C) tract, and it encodes a leader protein like that of other cardioviruses, unrelated to the aphthovirus-type leader.

3. Revised organisation
It is proposed to list VHEV as a separate species within the "TMEV cluster" (see proposal 5) of the cardiovirus genus, the encephalomyocarditis-like viruses comprising the other cluster. In addition to the genetic distance that separates them, these two clusters are distinguished by the presence in the latter of a poly(C) tract and the association of the former with chronic neurodegenerative disease.

4. Derivation of proposed name
No new names proposed.

5. References

¹ Pritchard, A.E., Strom, T. and Lipton, H.L. (1992) Nucleotide sequence identifies Vilyuisk virus as a divergent Theiler's virus. Virology 191:469-472.

² Michiels, T., Jarousse, J. and Brahic, M. (1995) Analysis of the leader and capsid coding regions of persistent and neurovirulent strains of Theiler's virus. Virology 214:550-558.

From the Picornavirus Study Group
Taxanomic proposal no. 4

1. Proposal
To classify equine rhinovirus type 1 (ERV1) within the genus Aphthovirus.

2. Purpose
It has long been known that ERV1, a currently unclassified picornavirus, has physico-chemical properties, e.g. acid lability, unlike those of human rhinoviruses, but similar to foot-and-mouth disease virus (FMDV)¹, of the genus Aphthovirus. The recently determined sequence of ERV1 RNA^2,3 reveals many other characteristics shared with the FMDVs. These features include (i) a poly(C) tract which is (ii) adjacent to a series of predicted pseudoknots, (iii) a type-I internal ribosome entry site, (iv) two in-frame AUG codons in locations, and sequence contexts, very similar to their counterparts in FMDV RNA, from which two forms of (v) an FMDV-like leader protein are predicted to be initiated, and (vi) a 2A proteinase gene of just 16 codons. Aside from (i) and (iii), which are shared also with the cardioviruses, these features are uniquely diagnostic of the aphthoviruses. Overall, the ERV1 sequence is significantly more closely related to FMDV than to any other picornavirus (including type 2 equine rhinovirus3, whose classification will be dealt with separately). Capsid proteins VP1-3 of ERV1 are FMDV-like in their distinctively short lengths, although there are several small insertions and deletions. Another difference from FMDV is the presence in ERV1 of only a single copy of the VPg gene.

While the close relationship between ERV1 and FMDV is sufficient reason to group them in one genus, the ICTV has objected on the grounds that ERV1 does not cause vesicular lesions and therefore can not literally be an aphtho virus. There are, however, many precedents where it is understood that the group name describes the type species, but not necessarily other members, of that group. There seems little necessity, therefore, to devise a new name for the aphthovirus genus.

3. Revised organisation
The genus will contain two clusters, the FMDVs comprising one, ERV1 the other.

4. Derivation of proposed name
No new names proposed.

5. References

¹ Newman, J.F.E., Rowlands, D.J., Brown, F., Goodridge, D., Burrows, R. and Steck, F. (1977). Physicochemical characterization of two serologically unrelated equine rhinoviruses. Intervirology 8:145-154.

² Li, F., Browning, G.F., Studdert, M.J. and Crabb, B.S. (1996) . Equine rhinovirus 1 is more closely related to foot-and-mouth disease virus than to other picornaviruses. Proc. Natl. Acad. Sci., USA, 93:990-995.

³ Wutz, G., Auer, H., Nowotny, N., Grosse, B., Skern, T. and Kuechler, E. (1996). Equine rhinovirus serotypes 1 and 2: relationship to each other and to aphthoviruses and cardioviruses. J. Gen. Virol. 77:1719-1730.