A27 Whole genome characterization of influenza D viruses detected in cattle herds in northern Italy between 2015 and 2017

Influenza D virus (IDV) is a new viral genus identified within the Orthomyxoviridae family, showing 50 per cent amino acid identity with human influenza C virus. Similar to human influenza viruses of the C genus, IDV also harbors 7 genomic segments and uses 9-O-acetylated sialic acids as cell receptors. This newly emerged virus exhibits a broad host range and is capable of infecting swine, cattle, sheep, goats, ferrets, and guinea pigs. In Italy, IDV was first detected in archived samples collected between 2014 and 2015 from cattle and swine in the Po Valley area. Here, we report the genetic characterization of IDV viruses detected in an extensive area of northern Italy, namely Veneto, Lombardy, and Piedmont, through passive surveillance between September 2015 and October 2017. A total of 482 samples, including nasal swabs, lungs, and bronchoalveolar lavage fluid, collected from 309 cattle farms were tested. Thirty cattle herds turned out to be positive, for a total of 40 samples positive by Real Time RT-PCR targeting the PB2 gene. Representative IDV positive swabs were sequenced on an Illumina Miseq platform, and phylogenetic analyses were performed for each genome segment. The analyses of the seven gene segments demonstrated that the viruses identified in the north of Italy clearly grouped within a genetic cluster of IDV sequences previously described in Italy and in the USA, thus suggesting a common origin for these viruses. Interestingly, the IDVs identified in Italy presented a low similarity (96.1% to 98.8% for the seven gene segments) to the French IDVs, which is the only other European country where this pathogen has been identified and characterized so far. The wide IDV host range and the ability of this virus to reassort are a matter of concern. Results of this study indicate that IDV is extensively circulating among bovine herds in Northern Italy and suggest a potential role of IDV in the bovine respiratory disease complex, highlighting the need to perform surveillance on an ongoing basis to track its spread and evolution.