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The genus is distinguished on the basis of genetic characters.
No surface morphology is visible by EM. The crystal structures of human parechovirus 1 and 3 and Ljungan virus 1 have been resolved (Zhu et al., 2015, Shakeel et al., 2016).
Virions are acid stable. The buoyant density in CsCl is 1.36 g cm-3.
Genome (Smits et al., 2013, Hyypia et al., 1992, Ghazi et al., 1998, Niklasson et al., 1999, Joffret et al., 2013): 7,339–7,608 nt (5′-UTR: 710–730 nt; ORF: 6,543–6,753; 3′-UTR: 87–111 nt). The 5′-UTR contains a typical type II IRES. The cre has been identified in the 1AB region for human parechoviruses and is thought to lie within the 3B region of Ljungan viruses.
The deduced polyprotein ranges from 2,180–2,250 aa. The polyprotein contains only a single protease (3Cpro). Members of Parechovirus B, C, D possess a 2A protein with NPG↓P motif. all parechoviruses have 2A protein with a H-box/NC motif.
Human parechoviruses replicate in the respiratory and gastrointestinal tract. Infection is particularly prevalent in infants and young children but it is probably often asymptomatic apart from infections with human parechovirus (HPeV) type 3 which can present with severe neonatal sepsis and central nervous system damage. In addition to respiratory infections and diarrhoea, infections of the central nervous system (encephalitis, meningitis, ataxia) have been reported. HPeV types 1 and 6 have been found in monkeys with diarrhoea, although disease association was not proven. The cytopathology may be unusual in including changes in granularity and chromatin distribution in the nucleus, when viewed in the electron microscope. Ljungan viruses appear to infect predominantly rodents (voles) and have been proposed to infect humans, however, conclusive data is awaited. Some human parechoviruses (types 1, 2, 4, 5 and 6) possess an RGD tri-peptide (towards the carboxy-terminus of 1D) which is involved in integrin receptor-binding. The integrins αvβ3 and αvβ6 have been shown to be the primary receptors for HPeV-1 in A549 cells. Receptor usage for the remaining human parechoviruses and Ljungan viruses is not known. Sebokele virus was detected in mice (Hylomyscus spec.) in the Central African Republic. Ferret parechovirus was detected in rectal swabs of ferrets (Mustela putorius furo).
Human parechoviruses are divided into 18 genetic types and there is no cross-neutralization between types 1, 2 and 3. There may be a cross-reaction between types 2 and 5, however, the remaining types have not been tested. Ljungan viruses are divided into five genetic types, but antigenic relationships have not been studied. Parechovirus C and D each contain one type.
Parecho-: from par(a)echo from pará Greek for beside, and echo, the former name of the type species, an acronym for "enteric, cytopathic, human, orphan"
At least 25 types have been characterized genetically by phylogenetic clustering: Parechovirus A (18 types), Parechovirus B (5 types), Parechovirus C (1 type), Parechovirus D (1 type).
Members of a species of the genus Parechovirus:
The divergence (number of differences per site between sequences) between members of different Parechovirus species ranges from 0.44–0.63 for P1 and 0.34–0.59 for 3CD.
Manhatten parechovirus [rat/NYC-A11/USA/2013]
parechovirus-like picornavirus [falcon/HA18_080/2014/HUN]
Yili teratoscincus roborowskii picornavirus 2 [LPWC210215]
Phylogenetic analysis indicates that these viruses may be members of novel Parechovirus species.
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