Pathogenesis and transmission studies: non-swine influenza A viruses in the swine host

Authors: ABENTE, EUGENIO - Orise Fellow; RAJAO, DANIELA - Non ARS Employee; Kitikoon, Pravina; Anderson, Tavis; Lager, Kelly; GAUGER, PHILLIP - Iowa State University; Baker, Amy

Submitted to: Swine Disease Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/27/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Abstract Influenza A virus (IAV) causes disease in poultry, pigs, and people with wild waterfowl being the natural reservoir. IAV strains have been periodically transmitted between swine and humans in both directions and avian IAV have also sporadically infected swine. If an individual is infected with two different IAV strains, the viral genes can mix or "reassort" to generate a virus that shares properties from both parental viruses, potentially making the progeny viruses more infectious or able to avoid previous immunity from vaccination or earlier infections. Since pigs may be infected with IAV from swine, human or avian sources, they pose a risk for such reassorting events. In three separate studies, we evaluated the ability to infect swine with five wildtype strains of highly pathogenic avian influenza (HPAI) subtypes H5N1, H5N2, and H5N8, and an H5N1 after reassortment with human 2009 pandemic H1N1 genes. A canine H3N2 virus was also evaluated. The wholly avian and canine viruses showed limited potential for infection or transmission in swine. However, we observed increased replication and transmission in the reassortant H5N1 that contained swine-adapted H1N1 genes. These findings highlight the restricted ability of these avian or canine IAV to infect pigs, but also caution the potential for HPAI viruses to incorporate genes from human or swine viruses and become more infectious to pigs. Introduction The Eurasian lineage of highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype have remained largely restricted to wild avian species, but may cause severe outbreaks in domestic poultry (1, 2). Recently, HPAI H5 were detected in North America and included H5N2, H5N8, and H5N1 subtypes (3). The U.S. viruses have been detected in wild birds, backyard poultry, and commercial chicken and turkey flocks, with the H5N2 subtype responsible for the commercial poultry outbreaks in the Midwest. Occasional transmission of H5N1 HPAI viruses to humans have been reported, especially of the Eurasian and Euro-African phylogenetic clades, and despite a lack of efficient human-to-human transmission (4, 5), H5N1 viruses are an important global health concern due to the high human case fatality rate observed with specific lineages of H5 hemagglutinin genes (~60%) (6). The Euro-African A lineage of HPAI H5N1 emerged outside of Asia around 2005, and was subsequently associated with a number of human cases, including those in Iraq and Egypt (7). With the relatively high number of human cases associated with the Middle Eastern HPAI H5N1 viruses, this lineage was selected for risk assessment alone or after reassortment with the 2009 H1N1 pandemic (H1N1pdm09) virus. Additionally, a new lineage of Asian avian-lineage H3N2 that had been detected in dogs in Asia since 2006 (8) was identified in dogs in the United States in 2015. This H3N2 is genetically and antigenically distinct from the former H3N8 that was previously responsible for canine influenza in the United States. This new H3N2 was first detected in the Chicago, IL area in March and then spread to other states, primarily in dogs associated with animal shelters, boarding kennels, dog day care facilities, dog parks, etc., in urban areas (https://ahdc.vet.cornell.edu/news/civchicago.cfm). It continued to be detected, with positive samples reported as recent as August 2015 (https://ahdc.vet.cornell.edu/docs/CIV_Monitoring_2015-08-08r.pdf). Since swine may be infected with some lineages of H5 HPAI and are endemically infected with human-seasonal origin H3N2 globally, the ability of these emerging viruses to infect pigs warrants further investigation. Additionally, since the H1N1pdm09 is endemic in many swine populations and is a seasonal human strain, there is a potential for a swine adapted or novel reassortant to emerge from these non-swine IAV subtypes and lineages if they were ab