Competition between IAV subtypes through heterosubtypic immunity modulates re-infection and antibody dynamics in the mallard reservoir

Abstract

Our overall hypothesis is that host population immunity directed at multiple antigens will influence the prevalence, diversity and evolution of influenza A virus (IAV) in avian populations where the vast subtype diversity is maintained. To investigate how initial infection influences the outcome of later infections with homologous or heterologous IAV subtypes and how viruses interact through host immune responses; we carried out experimental infections in mallard ducks (Anas platyrhynchos). Mallards were pre-challenged with an H3N8 low-pathogenic IAV and were divided into six groups. At five weeks post H3N8 inoculation, each group was challenged with a different IAV subtype or the same H3N8. Two additional pre-challenged groups were inoculated with the homologous H3N8 virus at weeks 11 and 15 after pre-challenge to evaluate the duration of protection, which showed that mallards were still resistant to re-infection after 15weeks. There was a significant reduction in shedding for all pre-challenged groups compared to controls and the outcome of the heterologous challenges varied according to hemagglutinin (HA) phylogenetic relatedness between the viruses used. There was a boost in the H3 antibody titer after re-infection with H4N5, which is consistent with original antigenic sin or antigenic seniority and suggest a putative strategy of virus evasion. These results imply strong competition between related subtypes that could regulate IAV subtype population dynamics in nature.Collectively, we provide new insights into within-host IAV complex interactions as drivers of IAV antigenic diversity that could allow the circulation of multiple subtypes in wild ducks. Author summaryMany features of pathogen diversification remain poorly explored although host immunity is recognized as a major driver of pathogen evolution. Influenza A viruses (IAVs) can infect many avian and mammalian hosts, but while few IAV subtypes circulate in human populations, subtype diversity is extensive in wild bird populations. How do these subtypes coexist in wild avian populations and do they compete within these natural host populations?Here we experimentally challenged mallard ducks with different IAVs to study how an initial infection with H3N8 determines the outcome of later infections (duration of infection and virus load) and antibody responses. There was complete protection to re-infection with the same H3N8 virus based on virus isolation. In addition, there was partial protection induced by H3N8 pre-challenge 3 to other subtypes and development of heterosubtypic immunity indicated by shorter infections and reduction in viral load compared to controls. This indicates that subtype dynamics in the host population are not independent. Amongst H3N8 pre-challenged groups, the highest protection was conferred to the H4N5 subtype which was most genetically related to H3N8. The H4N5challenge also induced an increase in H3 antibody levels and evidence for antigenic seniority.Thus, previous infections with IAV can influence the outcome of subsequent ...

Are Microneutralization and Hemagglutination Inhibition Assays Comparable? Serological Results from Influenza Experimentally Infected Mallard Ducks

“…A total of 345 paired serum samples from 75 mallards were collected at different time points in three previous studies (8,17,18). These studies were conducted at the University of Georgia, Athens, GA, USA.…”

“…All animals inoculated with the H3N8 virus tested positive by rRT-PCR and virus isolation at 2 days post-inoculation (DPI) in oropharyngeal and cloacal swabs. The patterns of infection after homo-or heterosubtypic challenges were variable (8,17,18). The experimental design varied between trials, but all serum samples were collected on 0 and 14 DPI from the brachial or jugular vein.…”

“…Given the benefits of the MN assay, our objective was to determine the correspondence between the results of HI and MN assays when duck serum samples were tested. For comparison, serum samples from mallards experimentally infected with H3N8 IAV and subsequently inoculated with homo-or heterosubtypic IAV were tested by both methods (8,18).…”

No evidence for homosubtypic immunity of influenza H3 in Mallards following vaccination in a natural experimental system

“…Further, there are fewer infections with phylogenetically closely related subtypes, suggesting partial or complete protection (heterosubtypic immunity) (Latorre‐Margalef et al . , ). Homosubtypic immunity and heterosubtypic immunity have also been demonstrated in infection experiments, especially for accessing vaccine outcomes against highly pathogenic H5 and H7 viruses (Fereidouni et al .…”