Abstract
Domestic mallards (Anas platyrhynchos domesticus) are traditionally used as a model to investigate infection dynamics and immune responses to low pathogenic avian influenza viruses (LPAIVs) in free-living mallards. However, it is unclear whether the immune response of domestic birds reflects the response of their free-living counterparts naturally exposed to these viruses. We investigated the extent to which the innate humoral immune response was similar among (i) wild-type domestic mallards in primary and secondary infection with LPAIV H4N6 in a laboratory setting (laboratory mallards), (ii) wild-type domestic mallards naturally exposed to LPAIVs in a semi-natural setting (sentinel mallards), and (iii) free-living mallards naturally exposed to LPAIVs. We quantified innate humoral immune function by measuring non-specific natural antibodies (agglutination), complement activity (lysis), and the acute phase protein haptoglobin. We demonstrate that complement activity in the first 3 days after LPAIV exposure was higher in primary-exposed laboratory mallards than in sentinel and free-living mallards. LPAIV H4N6 likely activated the complement system and the acute phase response in primary-exposed laboratory mallards, as lysis was higher and haptoglobin lower at day 3 and 7 post-exposure compared to baseline immune function measured prior to exposure. There were no differences observed in natural antibody and haptoglobin concentrations among laboratory, sentinel, and free-living mallards in the first 3 days after LPAIV exposure. Our study demonstrates that, based on the three innate humoral immune parameters measured, domestic mallards seem an appropriate model to investigate innate immunology of their free-living counterparts, albeit the innate immune response of secondary-LPAIV exposed mallards is a better proxy for the innate immune response in pre-exposed free-living mallards than that of immunologically naïve mallards.
Highlights
Low pathogenic avian influenza virus (LPAIV) is a zoonotic pathogen that circulates naturally in wild birds (Webster et al, 1992; Hurt et al, 2017)
We investigated the extent to which the innate humoral immune response was similar among (i) wild-type domestic mallards in primary and secondary infection with LPAIV H4N6 in a laboratory setting, (ii) wild-type domestic mallards naturally exposed to LPAIVs in a semi-natural setting, and (iii) free-living mallards naturally exposed to LPAIVs
We show that in primary-exposed laboratory mallards, LPAIV H4N6 likely activated the complement system and the acute phase response, as lysis was higher and haptoglobin lower at day 3 and 7 post-exposure compared to primary-baseline
Summary
Low pathogenic avian influenza virus (LPAIV) is a zoonotic pathogen that circulates naturally in wild birds (Webster et al, 1992; Hurt et al, 2017). Mallards (Anas platyrhynchos) are suggested to play an important role in the transmission of LPAIVs to domestic birds (chickens, turkeys, and ducks) and their wild counterparts, partly due to their great abundance (~19 million individuals), worldwide distribution, and preference for human-influenced environments (Wille et al, 2017). It has been suggested that LPAIVs do not induce strong innate immune responses in this reservoir host (Magor, 2011; Evseev and Magor, 2019). The influenza virus sensor RIG-I plays a key role in the innate immune response of domestic mallards Domestic mallards are traditionally used as a model to investigate the innate immune response to LPAIV in free-living mallards, it remains unclear how well these results reflect the immune response of their free-living counterparts upon natural exposure
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