Virological Surveillance of Influenza Virus Type A, B, C, D in Italy

Background Influenza A, B, C and D (IAV, IBV, ICV, IDV) viruses are genus of Orthomixoviridae family that can cause influenza in humans and animal. IAVs infect humans, mammal and avian species. IBV is considered a common seasonal human pathogen but can also infect pigs and seals , while ICV causes mild infection in humans. ICV has been isolated once from swine in China. IDV was first identified in 2011 in pigs with influenza-like illness but later researchers have found that IDV is widespread and fairly common in cattle IDV zoonotic role is under investigation. AIM: To investigate the circulation of IAV, IBV, ICV, IDV in cattle, swine and human in Italy. Methods Since 2015 onwards we performed a virological screening by real-time RT-PCR for influenza viruses on respiratory samples collected in Northern Italy from cattle (IBV, ICV, IDV) and swine (IAV, IBV, ICV, IDV) ). Full genomes of IAVs and IDVs were sequenced. Human samples collected during the InfluNet programme (annual active surveillance of IAV and IBV in humans), were examined for ICV and IDV by Real-time RT-PCR. Results Swine: we examined 856 herds and found 34% positive for IAV and 1.75% for IDV. IBV and ICV were not detected Cattle: we examined 888 herds and found 7.6% positive for IDV. IBV and ICV were not detected Humans: IAV or IBV were detected in 46.9% of the samples examined in the InfluNet programme in the Italian Area considered. We examined 1491 respiratory samples, IAV/ IBV negative, and we detected ICV in 0.7% of the examined cases. IDV was not detected. Genetic analysis of IDV from swine and cattle confirmed the circulation of viruses clustering with D/swine/Oklahoma/1334/2011 while the genetic analysis of IAVs from swine showed a more complicated situation with the circulation of multiple reassortant genotypes (H1N1,H1N2,H3N2). Conclusions The study showed cattle the most susceptible species to IDV infection whilst it was confirmed that IAV circulates with high prevalence among pigs. The high genotypic variability of Italian swine IAVs has undergone further growth. Circulation of ICV or IBV in cattle or swine was not demonstrated. The study did not prove IDV circulates among humans while ICV was detected only in 0.7% of respiratory illness. Despite a high positivity for IAV and IBV in humans, introduction of genes from human influenza viruses to animal species was limited to H1N1pdm 09 derived viruses detected in swine population.