Abstract
BackgroundIn the fall of 2014, highly pathogenic avian influenza (HPAI) subtype H5N8 clade 2.3.4.4 was introduced into North America by migrating waterfowl from Asia where, through reassortment, novel HPAI H5N2 and H5N1 viruses emerged.ObjectivesAssess the susceptibility of pigs to HPAI H5N1, H5N2, and H5N8 clade 2.3.3.3 from North America.MethodsPigs and trachea explants were inoculated with a representative panel of H5NX clade 2.3.4.4 HPAI viruses from North America. Nasal swabs, BALF, and sera were collected to assess replication and transmission in challenged and direct contact pigs by RRT‐PCR, virus isolation, hemagglutination inhibition, and ELISA.ResultsLimited virus replication was restricted to the lower respiratory tract of challenged pigs, though absent in the nasal passages and trachea cultures, as determined by RRT‐PCR in all samples. Seroconversion of inoculated pigs was detected by NP ELISA but was not reliably detected by antigen‐specific hemagglutination inhibition. Boost with adjuvanted virus was required for the production of neutralizing antibodies to assess cross‐reactivity between wild‐type avian strains. All RRT‐PCR and serology tests were negative for contact animals indicating a failure of transmission from primary inoculated pigs.ConclusionsH5NX clade 2.3.4.4 strains can replicate in the lower respiratory tract of swine upon high titer inoculation, though appear to be incapable of replication in swine nasal epithelium in vivo or ex vivo in trachea explants in culture. Infected pigs did not produce high levels of serum antibodies following infection. Collectively, our data show HPAI H5NX clade 2.3.4.4 viruses to be poorly adapted for replication and transmission in swine.
Highlights
In the fall of 2014, A/goose/Guangdong/1/1996 lineage clade 2.3.4.4 highly pathogenic avian influenza (HPAI) A viruses of the H5 subtype were introduced to the North American continent, presumably carried by infected migratory waterfowl, and subsequently isolated from wild birds in Western Canada and the Northwestern United States.[1,2,3,4]
Previous studies have shown that while North American H5NX viruses are low in virulence properties and non-transmissible in mice and ferrets, they remain highly pathogenic for many avian species.[6,7,8]
As pigs have been proposed to be more permissive for replication of avian influenza A viruses (IAV) compared to other mammalian species,[9,10] understanding whether H5NX clade 2.3.4.4 viruses can infect and transmit in swine is a primary concern in addressing the risk emerging IAV pose to agriculture and public health
Summary
In the fall of 2014, highly pathogenic avian influenza (HPAI) subtype H5N8 clade 2.3.4.4 was introduced into North America by migrating waterfowl from Asia where, through reassortment, novel HPAI H5N2 and H5N1 viruses emerged. Methods: Pigs and trachea explants were inoculated with a representative panel of H5NX clade 2.3.4.4 HPAI viruses from North America. BALF, and sera were collected to assess replication and transmission in challenged and direct contact pigs by RRT-PCR, virus isolation, hemagglutination inhibition, and ELISA. Results: Limited virus replication was restricted to the lower respiratory tract of challenged pigs, though absent in the nasal passages and trachea cultures, as determined by RRT-PCR in all samples. Conclusions: H5NX clade 2.3.4.4 strains can replicate in the lower respiratory tract of swine upon high titer inoculation, though appear to be incapable of replication in swine nasal epithelium in vivo or ex vivo in trachea explants in culture. KEYWORDS clade 2.3.4.4, H5, highly pathogenic avian influenza, influenza, North America, pigs, swine
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