Heterosubtypic immunity increases infectious dose required to infect mallard ducks to Influenza A Virus

Authors: SEGOVIA, KAREN - University Of Georgia; FRANCA, MONIQUE - University Of Georgia; LEYSON, CHRISTINA - University Of Georgia; Kapczynski, Darrell; CHRZASTEK, KLAUDIA - Orise Fellow; BAHNSON, CHARLIE - University Of Georgia; STALLKNECHT, DAVID - University Of Georgia

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2018
Publication Date: 4/26/2018
Citation: Segovia, K., Franca, M., Leyson, C.L., Kapczynski, D.R., Chrzastek, K., Bahnson, C.S., Stallknecht, D. 2018. Heterosubtypic immunity increases infectious dose required to infect mallard ducks to Influenza A Virus. PLoS One. 13(4):e0196394. https://doi.org/10.1371/journal.pone.0196394.
DOI: https://doi.org/10.1371/journal.pone.0196394

Interpretive Summary: Avian influenza (AI) viruses cause widespread morbidity and mortality in wild and domestic bird populations and threaten the U.S. poultry food supply and safety. The viruses vary widely in their pathogenicity and the ability to cause disease among birds. The viruses are divided into low pathogenic AI (LPAI) and highly pathogenic AI (HPAI) strains. Highly pathogenic AI is an economically important disease of poultry that has significant impact on global trade. New outbreaks of HPAI in commercial poultry represent one of the most critical diseases to contain and require reporting to the World Organization for Animal Health. In 2014-15, the United States sustained its worst foreign animal disease event following the original isolation and detection of HPAI in wild aquatic birds. In these studies, we tested if ducks previously exposure to LPAI viruses demonstrated resistance to infection from HPAI viruses. We demonstrate that immunity produced against LPAI viruses can inhibit infection by HPAI virus. These studies further our knowledge of new and ongoing HPAI outbreaks as well as transmission potential in wild birds.

Technical Abstract: Previous field and experimental studies have demonstrated that heterosubtypic immunity (HSI) is a potential driver of Influenza A virus (IAV) prevalence and subtype diversity in mallards. Prior infection with IAV can reduce viral shedding during subsequent reinfection with IAV that have genetically related hemagglutinins (HA). In this experiment, we evaluated the effect of HSI conferred by an H3N8 IAV infection against increasing challenge doses of closely (H4N6) and distantly (H6N2) related IAV subtypes in mallards. Thirty 1-month-old mallards were inoculated with 10(5.9) 50% embryo infectious doses (EID50) of an H3N8 virus. One month later, groups of five birds each were challenged with increasing doses of H4N6 or H6N2 virus; age-matched, single infection control ducks were included for all challenges. Results demonstrate that naïve birds were infected after inoculation with 10(3) and 10(4) EID(50) doses of the H4N6 or H6N2 virus, but not with 10(2) EID(50) doses of either IAV. In contrast, with birds previously infected with H3N8 IAV, only one duck challenged with 10(4) EID(50) of H4N6 IAV was shedding viral RNA at 2 days post-inoculation, and with H6N2 IAV, only birds challenged with the 10(4) EID(50) dose were infected. Viral shedding in ducks infected with H6N2 IAV was reduced on days 2 and 3 post-inoculation compared to control birds. To explain the differences in the dose necessary to produce infection among H3-primed ducks challenged with H4N6 or H6N2 IAV, we mapped the amino acid sequence changes between H3 and H4 or H6 HA on predicted three-dimensional structures. Most of the sequence differences occurred between H3 and H6 at antigenic sites A, B and D of the HA1 region. These findings demonstrate that the infectious dose necessary to infect mallards with IAV can increase as a result of HSI and that this effect is most pronounced when the HA of the viruses are genetically related.