The family Picornaviridae comprises small non-enveloped viruses with RNA genomes of 6.7 to 10.1 kb, and contains >30 genera and >75 species. Most of the known picornaviruses infect mammals and birds, but some have also been detected in reptiles, amphibians and fish. Many picornaviruses are important human and veterinary pathogens and may cause diseases of the central nervous system, heart, liver, skin, gastrointestinal tract or upper respiratory tract. Most picornaviruses are transmitted by the faecal–oral or respiratory routes. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Picornaviridae, which is available at www.ictv.global/report/picornaviridae.

PB1-F2 is a pro-apoptotic polypeptide of many influenza A virus (FLUAV) isolates encoded by an alternative ORF of segment 2. A comprehensive GenBank search was conducted to analyse its prevalence. This search yielded 2226 entries of 80 FLUAV subtypes. Of these sequences, 87 % encode a PB1-F2 polypeptide greater than 78 aa. However, classic swine influenza viruses and human H1N1 isolates collected since 1950 harbour a truncated PB1-F2 sequence. While PB1-F2 of human H1N1 viruses terminates after 57 aa, classic swine H1N1 sequences have in-frame stop codons after 11, 25 and 34 codons. Of the avian sequences, 96 % encode a full-length PB1-F2. One genetic lineage of segment 2 sequences which is avian-like and different from the classic swine FLUAV comprises PB1-F2 sequences of porcine FLUAVs isolated in Europe (H1N1, H1N2, H3N2). Of these PB1-F2 sequences, 42 % also exhibit stop codons after 11, 25 and 34 codons. These amino acid positions are highly conserved among all FLUAV isolates irrespective of their origin. Molecular genetic analyses reveal that PB1-F2 is under constraint of the PB1 gene. The PB1-F2 polypeptide of FLUAVs isolated from European pigs is expressed in host cells as demonstrated by immunohistochemistry. Using different PB1-F2 versions fused to an enhanced GFP, mitochondrial localization is demonstrated for those PB1-F2 polypeptides which are greater than 78 aa while a truncated version (57 aa) shows a diffuse cytoplasmic distribution. This indicates similar properties and function of porcine and human FLUAV PB1-F2.

The molecular classification of the porcine enterovirus (PEV) groups II and III was investigated. The sequence of the almost complete PEV-8 (group II) genome reveals that this virus has unique L and 2A gene regions. A reclassification of this group into a new picornavirus genus is suggested. PEV group III viruses are typical enteroviruses. They differ from other enteroviruses by a prolonged stem-loop D of the 5′-cloverleaf structure.

Genetic analysis of the M2 sequence of European porcine influenza A viruses reveals a high prevalence of amantadine resistance due to the substitution of serine 31 by asparagine in all three circulating subtypes, H1N1, H3N2 and H1N2. The M segment of all resistant strains belongs to a single genetic lineage. Whereas the first amantadine-resistant porcine strain was isolated in 1989, isolation of the last amantadine-susceptible strain dates to 1987, suggesting a displacement of amantadine-susceptible viruses by resistant strains soon after emergence of the mutation. Analysis of natural selection by codon-based tests indicates negative selection of codons 30, 31 and 34 which confer amantadine resistance. The codons 2, 11–28 and 54 of porcine and human strains exhibit differences in the patterns of substitution rates, suggesting different selection modes. Transfer of amantadine resistance by exchange of the M segment and viability of recombinant A/WSN/33 viruses with avian-like M segments raises concerns about the emergence of natural human reassortants.