Abstract
Surveillance of wild aquatic birds and free-range domestic ducks in the Tanguar Haor wetlands in Bangladesh has identified influenza virus subtypes H3N6, H7N1, H7N5, H7N9, and H15N9. Molecular characterization of these viruses indicates their contribution to the genesis of new genotypes of H5N1 influenza viruses from clade 2.3.2.1a that are dominant in poultry markets in Bangladesh as well as to the genesis of the highly pathogenic H5N8 virus currently causing disease outbreaks in domestic poultry in Europe and the Middle East. Therefore, we studied the antigenicity, replication, and pathogenicity of influenza viruses isolated from Tanguar Haor in the DBA/2J mouse model. All viruses replicated in the lung without prior mammalian adaptation, and H7N1 and H7N9 viruses caused 100% and 60% mortality, respectively. H7N5 viruses replicated only in the lungs, whereas H7N1 and H7N9 viruses also replicated in the heart, liver, and brain. Replication and transmission studies in mallard ducks showed that H7N1 and H7N9 viruses replicated in ducks without clinical signs of disease and shed at high titers from the cloaca of infected and contact ducks, which could facilitate virus transmission and spread. Our results indicate that H7 avian influenza viruses from free-range ducks can replicate in mammals, cause severe disease, and be efficiently transmitted to contact ducks. Our study highlights the role of free-range ducks in the spread of influenza viruses to other species in live poultry markets and the potential for these viruses to infect and cause disease in mammals.
Highlights
Wild aquatic birds are the primary natural reservoir for influenza A viruses (IAVs)[1]
The intravenous pathogenicity index (IVPI) of the seven viruses (A/duck/Bangladesh/26920/ 2015 H3N6, A/duck/Bangladesh/26948/2015 H3N6, A/ duck/Bangladesh/26918/2015 H3N6, A/duck/Bangladesh/24692/2015 H7N1, A/black-tailed godwit/Bangladesh/24734/2015 H7N5, A/duck/Bangladesh/26980/2015 H7N9, and A/duck/Bangladesh/24697/2015 H15N9) ranged from 0.0 to 0.05 in chickens (Supplementary Table S1), Antigenic characterization To determine antigenic relationships among influenza viruses isolated from free-range ducks and a wild bird, we analyzed H3, H7, and H15 viruses by using a panel of polyclonal and monoclonal antibodies (MAbs) against Eurasian and North American viruses
Almost all subtypes of avian IAVs (H1–H16 and N1–N9) have been identified in wild birds, and these birds have recently been implicated in the spread of highly pathogenic avian influenza (HPAI) H5N1 and H5N8 viruses
Summary
Wild aquatic birds are the primary natural reservoir for influenza A viruses (IAVs)[1]. Isolation and IVPI of influenza viruses from wild birds and free-range ducks Pathogenicity in DBA/2J mice To determine the ability of influenza subtypes isolated from free-range ducks and a wild bird to replicate and cause disease in mammals, the pathogenicity of 3 H3N6, 1 H7N1, 1 H7N5, 1 H7N9, and 1 H15N9 viruses was studied in DBA/2J mice.
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