Connecting the dots between swine influenza A virus surveillance and vaccines

Authors: Baker, Amy; Anderson, Tavis; KITIKOON, PRAVINA - MERCK RESEARCH LABORATORIES; LEWIS, NICOLA - UNIVERSITY OF CAMBRIDGE; RAJAO, DANIELA - NON ARS EMPLOYEE; CAMPBELL, BRIAN

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 12/3/2013
Publication Date: 3/1/2014
Citation: Vincent, A.L., Anderson, T.K., Kitikoon, P., Lewis, N., Rajao, D., Campbell, B.A. 2014. Connecting the dots between swine influenza A virus surveillance and vaccines. Proceedings of the 45th American Association of Swine Veterinarians Annual Meeting. p. 527-532.

Interpretive Summary:

Technical Abstract: Introduction Influenza A virus (IAV) infection was first recognized in the USA swine population following the 1918 Spanish flu pandemic in humans with the identification of an H1N1 virus that became known as the classical swine H1N1. In 1997-98, the incursion of the triple reassortant viruses with gene segments from human- (HA, NA, and PB1), swine- (NP and M) and avian- (PB2 and PA) adapted viruses changed the landscape of IAV in swine in the US and subsequently around the world.(1, 2) The establishment of the triple reassortant internal gene (TRIG) constellation is recognized as a critical turning point from that point in time into the present day, during which time we observed the TRIG viruses reassort numerous times to acquire new surface genes in the USA (beta, gamma, delta1- and delta2-H1N1 and H1N2; H2N3), to be exported to new regions (China and South Korea for example), and donate genes to the first human pandemic virus of the 21st century, H1N1pdm09.(3) Concurrent with frequent reassortment has been a dramatic evolution of IAV in swine in the USA, resulting in multiple antigenic variants that co-circulate and severely challenge our control measures. Efforts have heightened on the parts of the public and animal health sectors to increase monitoring IAV in the populations of interest to gain a better understanding of the overall ecology of IAV with the ultimate hopes of improved detection and control interventions. The U.S. Department of Agriculture (USDA) implemented a swine influenza surveillance system in 2009 in response to the growing concern over endemic swine IAV, sporadic zoonotic transmission events with swine adapted IAV, the emergence of the H1N1pdm09, and the subsequent spillover of H1N1pdm09 from humans to pigs. The USDA system, implemented by the National Animal Health Laboratory Network (NAHLN) veterinary diagnostic laboratories and dependent on the voluntary participation by veterinarians and producers, has overwhelmingly responded to concerns about the insufficient quantity of virological and molecular surveillance of IAV in the U.S. swine population.(4) Data from human and swine influenza sectors have provided invaluable insights into the nature of IAV adapted to swine and the implications of spillover that occurs in both directions between humans and pigs. Apart from H1N1pdm09, sporadic infection of humans with H1N1 and H1N2 swine IAV were increasingly reported since 2005, but none occurred with the magnitude of the recent H3N2v cases associated primarily with agricultural fairs and exhibitions,(5) underscoring the continued importance of control of IAV in swine for the benefit of both human and swine health. Virologic surveillance and virus evolution Recent improvements in influenza surveillance in US swine populations have made great strides toward timely epidemiological, phylogenetic, and virological analyses that monitor emergence of novel viruses and assess changes in viral population dynamics. Virologic surveillance is the foundation necessary to begin to fully understand the breadth of the issues with IAV in swine (Figure 1). However, in-depth sequence analysis, epidemiologic study, and antigenic evaluation must be tied to the surveillance activities. Finally, phenotyping studies with virus isolates from the surveillance system may be needed to assess virulence and transmission properties as well as for testing the efficacy of existing or experimental vaccines when genetic changes or reassortants are recognized. Since the inception of the USDA surveillance system, over 37,500 pigs have been tested from approximately 9,800 accessions, with over 3,300 positive accessions and approximately 1,500 virus isolations (J. Korslund, USDA-NSU, personal communication). Acceptance and participation in the USDA system has continued to grow each year, thanks to producer and veterinarian support. Phylogenetic