Infectious salmon anaemia virus (ISAV) is an orthomyxovirus causing a multisystemic, emerging disease in Atlantic salmon. Here we present, for the first time, detailed sequence analyses of the full-genome sequence of a presumed avirulent isolate displaying a full-length hemagglutinin-esterase (HE) gene (HPR0), and compare this with full-genome sequences of 11 Norwegian ISAV isolates from clinically diseased fish. These analyses revealed the presence of a virulence marker right upstream of the putative cleavage site R267 in the fusion (F) protein, suggesting a Q266-->L266 substitution to be a prerequisite for virulence. To gain virulence in isolates lacking this substitution, a sequence insertion near the cleavage site seems to be required. This strongly suggests the involvement of a protease recognition pattern at the cleavage site of the fusion protein as a determinant of virulence, as seen in highly pathogenic influenza A virus H5 or H7 and the paramyxovirus Newcastle disease virus.

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We report a rapid increase in enterovirus D68 (EV-D68) infections, with 139 cases reported from eight European countries between 31 July and 14 October 2021. This upsurge is in line with the seasonality of EV-D68 and was presumably stimulated by the widespread reopening after COVID-19 lockdown. Most cases were identified in September, but more are to be expected in the coming months. Reinforcement of clinical awareness, diagnostic capacities and surveillance of EV-D68 is urgently needed in Europe.

Uncultivable HPR0 strains of infectious salmon anaemia viruses (ISAVs) infecting gills are non-virulent putative precursors of virulent ISAVs (vISAVs) causing systemic disease in farmed Atlantic salmon (Salmo salar). The transition to virulence involves two molecular events, a deletion in the highly polymorphic region (HPR) of the hemagglutinin-esterase (HE) gene and a Q266→L266 substitution or insertion next to the putative cleavage site (R267) in the fusion protein (F). We have performed ultra-deep pyrosequencing (UDPS) of these gene regions from healthy fish positive for HPR0 virus carrying full-length HPR sampled in a screening program, and a vISAV strain from an ISA outbreak at the same farming site three weeks later, and compared the mutant spectra. As the UDPS data shows the presence of both HE genotypes at both sampling times, and the outbreak strain was unlikely to be directly related to the HPR0 strain, this is the first report of a double infection with HPR0s and vISAVs. For F amplicon reads, mutation frequencies generating L266 codons in screening samples and Q266 codons in outbreak samples were not higher than at any random site. We suggest quasispecies heterogeneity as well as RNA structural properties are linked to transition to virulence. More specifically, a mechanism where selected single point mutations in the full-length HPR alter the RNA structure facilitating single- or sequential deletions in this region is proposed. The data provides stronger support for the deletion hypothesis, as opposed to recombination, as the responsible mechanism for generating the sequence deletions in HE.

Acute gastroenteritis (AGE) has a major impact on morbidity and mortality worldwide. The viral aetiology of diarrhoeal diseases may remain unknown due to limited diagnostic facilities. Non-polio enteroviruses (NPEVs) are the third most frequent pathogen detected in stool specimens from AGE cases, yet their potential role in AGE is uncertain. In Nepal, limited data are available on NPEVs, due to both the lack of an adequate surveillance program and the availability of tests. The global polio eradication initiative effort of the WHO has eradicated the incidence of poliomyelitis and acute flaccid paralysis (AFP) from many parts of the world, including Nepal. However, cases of AFP associated with NPEVs have been reported in different countries, including the neighbouring India. This study aims to investigate the diarrhoeal stool samples from a birth cohort until the age of 36 months for NPEVs and the genotype diversity of NPEV in community children with diarrhoea. A total of 280 longitudinal diarrhoeal stool samples that were negative for other enteric pathogens were tested using RT-PCRs. NPEVs was detected in 97 stool specimens (34.6%) and were significantly more frequent in infants up to one year of age. This study identified 17 various NPEV types, with the dominating species being Enterovirus B (EV-B). Ten different types of echoviruses were recorded in this study, with the two rare NPEVs B74 and A120. Based on prevalence, seasonality, and diversity, further studies are warranted to investigate the role of enterovirus in diarrhoeal disease.