Pathogenicity of H3N8 influenza viruses isolated from domestic ducks in chickens with or without Escherichia coli coinfections.

Influenza viruses from domestic aquatic birds can be transmitted to chickens, resulting in continued prevalence of the disease. H3 viruses are one of the most frequently identified subtypes in domestic ducks. Results from our previous serologic study suggested that H3 virus infections potentially exist in chickens with a wide geographical distribution in China. To better understand their pathogenic potential, two H3N8 influenza viruses isolated from domestic ducks were selected for experimental infections in chickens. We found that viral shedding lasted for at least 14 days postinfection for both viruses; however, one virus caused mortality in the chickens when coinfected with Escherichia coli. Sequencing of the viral HA gene isolated from the inoculated chickens revealed two amino acid mutations within the gene. These findings demonstrate the pathogenicity of the H3N8 domestic duck influenza viruses to chickens, highlighting the need for routine epidemiologic investigations of H3 subtype influenza viruses in chicken populations.

Genetic analysis of H3 subtype influenza viruses isolated from domestic ducks in northern China during 2004-2005.

The broad distribution and prevalence of H3 subtype influenza viruses in avian and mammalian hosts constitutes a global threat to both human and veterinary health. In this present study, six H3N8 influenza viruses isolated from domestic ducks during 2004-2005 in northern China were genetically and phylogenetically characterized. Sequence analysis showed that HA, NA, and M genes of all the six H3N8 isolates had a close relationship with those of Equine/Jilin/1/89 (H3N8) virus, which once caused outbreak in equine populations in northern China. The PB2 and PA genes of the viruses possessed the highest similarities with highly pathogenic avian H5N1 influenza viruses currently circulating in this region. These findings emphasize the importance of avian influenza virus surveillance in this region for understanding the genesis and emergency of novel reassortants with pandemic potential.