Examining the role of adaptive heterosubtypic immunity in the epidemiology of low pathogenic avian influenza viruses in mallards
Segovia Hinostroza, Karen Melissa
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Influenza A virus (IAV) is a highly contagious pathogen that represents one of the most serious threats to animals and humans worldwide. Wild waterfowl from the order Anseriformes and Charadriiformes are considered the natural reservoirs for all subtypes of IAV. Several factors such as seasonality, spatial dynamics, host density, and immunity contribute to the epidemiology of IAV in these host populations. The primary goal of this research was to provide a better understanding of the role of heterosubtypic immunity (HSI) in the epidemiology of IAV in mallards. Our first objective was to evaluate the protective effect induced by prior infection with H3N8 LPAIV inoculation against subsequent infections with closely and distantly related LPAIV subtypes at different time points. Also, we wanted to determine if subsequent inoculation of birds with different IAV subtypes has a boosting effect on induction of this cross-protective immunity. The results demonstrated that the duration and extent of viral shedding was reduced in birds that had previously been infected with H3N8 and these effects were most pronounced when challenged with IAV subtypes genetically related by the hemagglutinin (HA); also, these effects were boosted with each subsequent infection. Our second objective was to determine if previous infection with H3N8 and resulting HSI increased the infective dose of closely (H4N6) and distantly (H6N2) related LPAIV during subsequent challenge in mallards. In both cases, the required infective dose was higher in birds previously infected with H3N8 as compared to naïve birds and this increase was most apparent with the more closely genetically related H4N6 virus. Our third objective was to determine the agreement between the microneutralization and hemagglutination inhibition assays for antibody detection in sera of mallards experimentally infected with the H3N8 virus. We found a slight to substantial agreement between the assays when samples were tested at different time-points. Overall, the host and viral factors investigated in this research demonstrated that HSI could be an important factor related to seasonal IAV prevalence and subtype diversity in waterfowl, and the potential for new viruses to successfully establish in mallards and other waterfowl in nature.