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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.
Length of 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 has lengths ranging from 2,180-2,250 aa. The polyprotein contains only a single protease (3Cpro). The 2A protein is believed to lack protease activity and is related distantly to a family of cellular proteins involved in the control of cell proliferation (H-box/NC motif). Ljungan virus possesses an NPG↓P motif following the predicted 1D polypeptide, suggesting the possible presence of a second 2A; however, it is believed that this short 2A-like sequence may form part of 1D.
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.
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 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.
Members of a species of the genus Parechovirus:
The divergence (number of differences per site between sequences) of known Parechovirus species ranges from 0.44-0.63 for P1 and 0.34-0.59 for 3CD.
Parecho: from par(a)echo (echo, the former name of the type species, an acronym for "enteric, cytopathic, human, orphan")
Manhatten parechovirus [rat/NYC-A11/USA/2013]
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