Type Species

Human parechovirus

(HPeV)

Virion Properties

Nucleic Acid

Predicted protein sequences of parechoviruses are highly divergent, no protein having a greater than 30% level of identity when compared with any other picornavirus.

Proteins

In contrast to most other picornaviruses, protein 1AB of parechoviruses appears not to be cleaved, and its N-terminus, also unusually, is not myristylated. The mature capsid therefore appears to comprise only three proteins, 1AB, 1C and 1D.

Biological Properties

Viruses primarily multiply in the gastrointestinal tract causing diarrhea, frequently with respiratory complications. Infection is particularly prevalent in young children. The cytopathology may be unusual in including changes in granularity and chromatin distribution in the nucleus, when viewed in the electron microscope.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:

Species in the Genus

Human parechovirus (2 serotypes)

(HPeV)

Human parechovirus 1 (formerly Human echovirus 22)

[L02971]

(HPeV-1)

Human parechovirus 2 (formerly Human echovirus 23)

[AJ005695]

(HPeV-2)

Tentative Species in the Genus

None reported.

Unassigned Species in the Family

Equine rhinitis B virus (formerly Equine rhinovirus 2)

[X96871]

(ERBV)

Distinguishing Features

ERBV sediments in CsCl with a density of 1.41-1.45 g/cm³. The virus is unstable below pH 5. ERBV possesses an usually long 3-NTR of 167 nts. At the 5-end, a poly(C) tract is thought to be present. No pseudoknots have been identified. The IRES is of type 2. The CPs have between 25% and 47% identity to those of ERAV, FMDV and EMCV, though protein modeling studies indicate that they are more closely related to those of EMCV. No evidence for alternative sites of initiation of protein synthesis is available. The L protein appears to be a proteinase, but has only 23% and 18% identity to the L protein of FMDV and ERAV, respectively. The 2B and 3C proteins have exceptionally large chain lengths (283 and 251 aa). The 2A protein has a chain length of 18 aa, ending in NPGP, and there is only one VPg. ERBV causes upper respiratory disease in horses, with a viraemia and faecal shedding. Infections may be permanent.

Aichi virus

[AB010145]

(AiV)

Distinguishing Features

Unlike other picornaviruses, Aichi virus (AiV) exhibits icosahedral surface structure under the electron microscope. Virions are stable at pH 3.5. The genome [AB010145] has a high G+C base composition (approx. 59%), and a very long 3-NTR (240 nts). Protein 1AB appears not to be cleaved. There is a leader polypeptide of unknown function, and distinctive length (170 aa rather than 67 aa or 217 aa in EMCV and FMDV, respectively). AiV grows in cell cultures (BS-C-1, Vero). AiV is thought to be a cause of human gastroenteritis.

Porcine teschovirus (formerly Porcine enterovirus 1)

(PTV)

Distinguishing Features

Virions are stable at acid pH. Buoyant density in CsCl is 1.33 g/cm³. Empty capsids are often observed in virus preparations. Genomes encode a single VPg and a leader (L) protein. The 2A polypeptide is very short (aa), and ends in NPGP. Clinical manifestations may include a polioencephalomyelitis which may differ in severity.

List of Species with Similar Properties

Porcine teschovirus 1

(PTV-1)

Porcine enterovirus 2-7

(PEV-2 to 7)

Porcine enterovirus 11-13

(PEV-11 to 13)

List of Unassigned Viruses in the Family

Acid-stable equine picornaviruses

(EqPV)

Avian entero-like virus 2 to 4

(AELV-2 to 4)

Avian nephritis virus 1 to 3

(ANV-1 to 3)

Barramundi virus-1

(BaV)

Cockatoo entero-like virus

(CELV)

Duck hepatitis virus 1

(DHV-1)

Duck hepatitis virus 3

(DHV-3)

Equine rhinovirus 3

(ERV-3)

Guineafowl transmissible enteritis virus

(GTEV)

Harbour seals picorna-like virus

(SPLV)

Ljungan virus^*

[AF020541]

(LV)

Sea-bass virus-1

(SBV)

Sikhote-Alyn virus

(SAV)

Smelt virus-1

(SmV-1)

Smelt virus-2

(SmV-2)

Syr-Daria Valley fever virus

(SDFV)

Taura syndrome virus of marine penaeid shrimp

(TSV)

Turbot virus-1

(TuV-1)

Turkey entero-like virus

(TELV)

Turkey hepatitis virus

(THV)

Turkey pseudo enterovirus 1 to 2

(TPEV-1, 2)

^* Ljungan virus is most closely related to the parechoviruses.

The significance of the reported serological cross-reaction between Cricket paralysis virus and EMCV is not presently understood.

Phylogenetic Relationships within the Family

See Fig. 4.

Similarity with Other Taxa

The “picornavirus superfamily” comprises the families Picornavriridae, Sequiviridae, Comoviridae, and Potyviridae, which share the following features:

1.

Genome: This consists of one, or two (in the case of the bipartite plant viruses) molecules (segments) of ssRNA of positive sense. Each segment acts as the exclusive mRNA for the genes it carries (i.e., there are no sgRNAs), contains a single ORF, and is linked to its 5-proximal via an O-phosphate ester bond to a tyrosine or serine residue of a genome-linked protein (VPg).

2.

Gene expression: The single polyprotein encoded by each genome segment is processed proteolytically to functional proteins by proteases, and these proteases are exclusively virus encoded.

3.

Genes: All members of the superfamily encode, in addition to VPg, a 2C-like protein having a nucleotide binding sequence motif, a 3C^pro-like protease, and a 3D^pol-like polymerase.

4.

Gene maps: The gene order, 2C-VPg-3C^pro-3D^pol, is common to all members of the superfamily, the 3D^pol gene always being located at the 3-terminus of the relevant ORF. Similarly, where CP gene(s) are present in an ORF, they are always 5-proximal.

5.

Virion structure: There is considerable morphological variation within the superfamily, which contains both icosahedral and rod-shaped viruses. However, the two icosahedral representatives whose crystal structures are known, Picornaviridae and Comoviridae, exhibit the same, pseudo T = 3, arrangement of three major protein subunits, which, themselves share the same, -barrel, tertiary structure.

Derivation of Names

Aphtho: from Greek aphtha, “vesicles in the mouth”; English: aphtho, “thrush”; French: fièvre aphteuse.

Cardio: from Greek kardia, “heart”.

Entero: from Greek enteron, “intestine”.

Hepato: from Greek hepatos, “liver”.

Parecho: from par(a)echo (echo, the former name of the type species, = the sigla for “enteric cytopathic human orphan”).

Picorna: from the prefix “pico” (= ‘micro-micro’) and RNA.

Rhino: from Greek rhis, rhinos, “nose”.


Human parechovirus (2 serotypes)		(HPeV)
Human parechovirus 1 (formerly Human echovirus 22)	[L02971]	(HPeV-1)
Human parechovirus 2 (formerly Human echovirus 23)	[AJ005695]	(HPeV-2)


Equine rhinitis B virus (formerly Equine rhinovirus 2)	[X96871]	(ERBV)


Porcine teschovirus 1	(PTV-1)
Porcine enterovirus 2-7	(PEV-2 to 7)
Porcine enterovirus 11-13	(PEV-11 to 13)


Acid-stable equine picornaviruses		(EqPV)
Avian entero-like virus 2 to 4		(AELV-2 to 4)
Avian nephritis virus 1 to 3		(ANV-1 to 3)
Barramundi virus-1		(BaV)
Cockatoo entero-like virus		(CELV)
Duck hepatitis virus 1		(DHV-1)
Duck hepatitis virus 3		(DHV-3)
Equine rhinovirus 3		(ERV-3)
Guineafowl transmissible enteritis virus		(GTEV)
Harbour seals picorna-like virus		(SPLV)
Ljungan virus^*	[AF020541]	(LV)
Sea-bass virus-1		(SBV)
Sikhote-Alyn virus		(SAV)
Smelt virus-1		(SmV-1)
Smelt virus-2		(SmV-2)
Syr-Daria Valley fever virus		(SDFV)
Taura syndrome virus of marine penaeid shrimp		(TSV)
Turbot virus-1		(TuV-1)
Turkey entero-like virus		(TELV)
Turkey hepatitis virus		(THV)
Turkey pseudo enterovirus 1 to 2		(TPEV-1, 2)

1.	Genome: This consists of one, or two (in the case of the bipartite plant viruses) molecules (segments) of ssRNA of positive sense. Each segment acts as the exclusive mRNA for the genes it carries (i.e., there are no sgRNAs), contains a single ORF, and is linked to its 5-proximal via an O-phosphate ester bond to a tyrosine or serine residue of a genome-linked protein (VPg).
2.	Gene expression: The single polyprotein encoded by each genome segment is processed proteolytically to functional proteins by proteases, and these proteases are exclusively virus encoded.
3.	Genes: All members of the superfamily encode, in addition to VPg, a 2C-like protein having a nucleotide binding sequence motif, a 3C^pro-like protease, and a 3D^pol-like polymerase.
4.	Gene maps: The gene order, 2C-VPg-3C^pro-3D^pol, is common to all members of the superfamily, the 3D^pol gene always being located at the 3-terminus of the relevant ORF. Similarly, where CP gene(s) are present in an ORF, they are always 5-proximal.
5.	Virion structure: There is considerable morphological variation within the superfamily, which contains both icosahedral and rod-shaped viruses. However, the two icosahedral representatives whose crystal structures are known, Picornaviridae and Comoviridae, exhibit the same, pseudo T = 3, arrangement of three major protein subunits, which, themselves share the same, -barrel, tertiary structure.