Antigenic distance of swine H3N2 and human seasonal strains as an indication of risk to human populations

Authors: SOUZA, CARINE - Orise Fellow; Anderson, Tavis; VENKATESH, DIVYA - University Of Cambridge; BOLTON, MARCUS - Orise Fellow; Abente, Eugenio; LEWIS, NICOLA - University Of Cambridge; Baker, Amy

Submitted to: International Symposium on Neglected Influenza Viruses
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2018
Publication Date: 4/18/2018
Citation: Souza, C.K., Anderson, T.K., Venkatesh, D., Bolton, M., Abente, E.J., Lewis, N., Vincent, A.L. 2018. Antigenic distance of swine H3N2 and human seasonal strains as an indication of risk to human populations [abstract]. International Symposium on Neglected Influenza Viruses. Abstract No. P23.

Interpretive Summary:

Technical Abstract: H3N2 influenza A viruses (IAV) cause seasonal epidemics in humans. Globally, human-to-swine interspecies transmission events occur repeatedly, leading to H3N2 lineages that circulate in pigs and to increased viral diversity in pig populations. In North America, an H3N2 incursion occurred in the late 1990s and genetically evolved into a swine lineage named as cluster IV (CIV). Recently, a 2010 human H3N2 incursion was detected in U.S. swine, and has become the predominant H3N2 lineage in the U.S. pig population. It was also associated with a number of human variant detections in 2016 and 2017. These events highlight the potential for re-emergence of IAV from swine back into humans. Here, we quantified antigenic distance between human seasonal and endemic swine H3N2 with hemagglutination inhibition (HI) assays and antigenic cartography, utilizing a panel of monovalent anti-sera raised in pigs against human seasonal H3N2 vaccine strains from 1973–2013 and contemporary swine strains from U.S., Mexico, Canada and Denmark. Antigenic distances between viruses were calculated in antigenic units (AU), in which 1 AU is equivalent to a 2-fold loss in HI cross-reactivity. Contemporary CIV swine strains demonstrated a closer antigenic relationship with human strains from the late 1980s and early 1990s: 2.4–5.2 AU for US, 1.0–5.9 AU for Mexico, and 2.6–6.4 AU for Canada swine strains. The contemporary swine IAV strains were most antigenically similar to human strains that were likely circulating when the initial human-to-swine spillover occurred. However, the CIV swine viruses were at least 5 AU from the latest decade of human vaccine strains. In contrast, 2010 U.S. and 2004 Danish human-like swine strains demonstrated substantial antigenic distance from human vaccine strains isolated prior to 2007 (>5.0 AU), and were more closely related to human seasonal strains from the last decade (0.4–4.3 AU). Our swine sera raised against human antigens may represent human population immunity, and therefore our approach may be used to identify swine H3N2 for further risk characterization by HI against age-stratified human sera, receptor binding assays, or other risk models. Strains from other countries/regions will be evaluated to understand the global extent of antigenic diversity at this important human-animal IAV interface.