Research Updates: Experimental Evaluation of 2009 Pandemic A/H1N1 in Pigs

Authors: Baker, Amy; Lager, Kelly; Harland, Michelle; CIACCI-ZANELLA, JANICE - Labex - Embrapa; ZANELLA, ERALDO - Universidad De Passo Fundo; Kehrli Jr, Marcus; GAUGER, PHILIP - Iowa State University; JANKE, BRUCE - Iowa State University; KLIMOV, ALEXANDER - Centers For Disease Control And Prevention (CDC) - United States

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2010
Publication Date: 3/6/2010
Citation: Vincent, A.L., Lager, K.M., Harland, M.L., Lorusso, A., Ciacci-Zanella, J.R., Zanella, E.L., Kehrli, Jr., M.E., Gauger, P.C., Janke, B.H., Klimov, A. 2010. Research Updates: Experimental Evaluation of 2009 Pandemic A/H1N1 in Pigs. In: Proceedings of the 41st Annual Meeting of the American Association of Swine Veterinarians, March 6-9, 2010, Omaha, Nebraska. p. 495-497.

Interpretive Summary:

Technical Abstract: Introduction: In March 2009, a novel pandemic A/H1N1 emerged in the human population in North America (2). The gene constellation of the emerging virus was demonstrated to be a combination of genes from swine influenza A viruses (SIV) of North American and Eurasian lineages that had never before been identified in swine or other species. The emergent A/H1N1 quickly spread in the human population and the outbreak reached pandemic level 6 as declared by the World Health Organization on June 11, 2009. Although the 8 gene segments of the novel virus have lineage with available sequences of corresponding genes from SIV from North America and Eurasia, no closely related ancestral SIV with this gene combination has been identified in North America or elsewhere in the world (10,11). Other than sporadic transmission to humans (6,9), swine influenza A viruses of the classical H1N1 subtype historically have been distinct from avian and other mammalian H1N1 influenza viruses in characteristics of host specificity, serologic cross-reactivity, and/or nucleotide sequence. However, spillover of human pandemic viruses to swine occurred following the Spanish flu pandemic of 1918 (H1N1) and the Hong Kong flu pandemic of 1968 (H3N2), and spillover of human seasonal viruses occurred in 1997 (H3N2) and 2003 (H1N1). In North America, multiple subtypes of endemic SIV (H3N2, H1N1, and H1N2) with a triple reassortant internal gene (TRIG) constellation derived from swine, avian and human influenza viruses co-circulate in most major swine producing regions of the U.S. and Canada since 1997-98 [reviewed in (14)]. Additionally, introduction of H1N1 and H1N2 viruses with the HA and NA genes originating from contemporary human seasonal influenza A viruses (hu-like H1) that are genetically and antigenically distinct from the classical swine H1 lineage were reported in pigs in Canada (4). Since 2005, hu-like H1N1 and H1N2 viruses have emerged in swine herds across the U.S. as human-swine reassortants possessing the TRIG (13). Four phylogenetic clusters (alpha, beta, gamma, and delta) of H1 SIV are now endemic in U.S. swine (13,15). However, to date, Eurasian lineage SIVs have not been reported in the U.S., thus the potential impact of transmission of the pandemic H1N1 virus to the U.S. pig population is unknown. This presentation will summarize a series of studies conducted at the USDA-ARS National Animal Disease Center evaluating the pandemic 2009 A/H1N1 in swine. Materials and methods. A/California/04/2009 (CA/09), A/New York/18/2009 (NY/09), and A/Mexico/4108/2009 (MX/09) received from the Centers for Disease Control and Prevention (CDC) were propagated in Madin-Darby Canine Kidney (MDCK) cells for use in the studies described below. Cross-bred pigs from a herd free of SIV and porcine reproductive and respiratory syndrome virus (PRRSV) were housed in ABSL3 containment and cared for in compliance with the Institutional Animal Care and Use Committee of the National Animal Disease Center. For pathogenesis studies (Studies 1 and 2), pigs were challenged at approximately 4-5 weeks of age. In Study 2, naïve contact pigs were placed with primary challenged pigs to evaluate transmission to direct and indirect contacts. To evaluate vaccine efficacy (Study 3), pigs were vaccinated with 2 mL of each vaccine by the intramuscular route at approximately 4 weeks of age, boosted at 7 weeks of age, and challenged at 10 weeks of age. Pigs were inoculated intra-tracheally with 2 mL of 1 x 10**5 50% tissue culture infectious dose (TCID50) of CA/09 or MX/09 as previously described (15). Pigs were observed twice daily for signs of clinical disease and fever. Nasal swabs were taken and placed into 2 mL minimal essential medium (MEM) on 0, 1, 2, 3, 4, 5 and/or 7 days post infection (dpi) to evaluate nasal virus shedding and stored at 80°C until study completion. In Studies 1