All sera positive for anti-AIV-NP antibodies were subsequently tested at the NCFAD for antibodies specifically against subtype H5 using an in-house developed cELISA that detects antibodies against all clades of subtype H5 [39]

All sera positive for anti-AIV-NP antibodies were subsequently tested at the NCFAD for antibodies specifically against subtype H5 using an in-house developed cELISA that detects antibodies against all clades of subtype H5 [39]. == Swab samples and RNA extraction == Oropharyngeal and cloacal swabs were collected from all individuals from 2022 to 2023 and the paired swabs SIRT-IN-1 were pooled into a single tube of Multitrans viral transport medium (Starplex Scientific, Product # S160-100) and represent a single sample per individual. February 2023 following a second H5N1 incursion from Eurasia. As expected, population-level immunity waned over time, with SIRT-IN-1 ducks seropositive for anti-AIV-NP antibodies for approximately twice as long as for H5-specific antibodies, with the population seronegative to the latter after approximately six months. We observed a clear relationship of increasing antibody levels with decreasing viral RNA loads that allowed for interpretation of the course of contamination and immune response in infected individuals and applied these findings to two cases of resampled ducks to infer contamination history. Our study highlights the value of applying both AIV surveillance and seroprevalence monitoring to provide a better understanding of AIV dynamics in wild populations, which may be crucial following the global dissemination of clade 2.3.4.4b H5Nx subtypes to assess the threats they pose to both wild and domestic animals, and to humans. == Supplementary Information == The online version contains supplementary material available SIRT-IN-1 at 10.1186/s13567-024-01397-5. Keywords:Highly pathogenic avian influenza computer virus, H5N1, serology, resident and migratory ducks, immunity == Introduction == Wild birds are the reservoir hosts of avian influenza viruses (AIVs), with waterfowl being one of the main reservoir groups and vectors by which AIVs are spread, along with gulls, shorebirds, and seabirds [14]. Low pathogenic avian influenza computer virus (LPAIV) contamination of waterfowl rarely results in overt disease symptoms, with birds usually clearing the infection within a matter of days. Dabbling ducks (Anatinae) infected with highly pathogenic avian influenza computer virus (HPAIV) H5Nx subtypes, similar to LPAIV contamination, can be minimally affected while shedding large quantities of computer virus, with moderate disease symptoms and delayed local movements in some cases [58]. While many species of diving ducks (Aythyinae) also appear to be minimally affected, some such as tufted ducks (Aythya fuligula) have been shown to be particularly prone to experience symptomatic HPAIV H5Nx infections and can exhibit severe contamination outcomes and high rates of mortality [6,9,10]. Recently, higher mortality in dabbling ducks due to HPAIV infections has been observed, representing a new pattern in one of the main reservoir hosts [1012]. HPAI clade 2.3.4.4 H5Nx viruses have been circulating with increasing frequency in wild birds in Eurasia and Africa since 2005 [9,1315], with the first incursion of A/goose/Guangdong/1/1996 (GsGd) lineage H5N8 clade 2.3.4.4 viruses into North America taking place in 2014 [16]. This computer virus, and a reassortant H5N2, did not persist and become established in North American wild bird populations. However, new incursions of clade 2.3.4.4b viruses starting in late 2021 have resulted in extensive reassortment with North American lineage LPAIVs, common blood circulation of H5Nx viruses throughout North and South America within a wide array of avian hosts, and multiple spillover events into mammals [1720]. These HPAIVs now seem to be part of the endemic viral populace in wild birds in the Americas, Eurasia, and Africa. AIV surveillance in wild birds has been a global focus for decades and has contributed to understanding viral dynamics and identifying circulating strains in different regions and species. However, this has not been without difficulties. Non-gallinaceous birds infected with LPAIVs are usually asymptomatic and test positive for viral RNA for only a very short period, generally 511 days [2125], providing a thin sampling windows for the detection of active infections. An increasing number of serological studies have helped address this shortcoming, by which past AIV contamination can be documented via detection of anti-AIV antibodies in the peripheral blood circulation for a period of months [24,2628]. A combined approach of AIV contamination surveillance and serology can therefore help capture AIV dynamics in more detail and over a longer time frame, allowing interpretation of both active and past infections in populations [8,29,30]. A HPAI H5N1 clade 2.3.4.4b computer virus was identified in a great black-backed gull (GBBG,Larus marinus) that died in November 2021 in St. Johns, Newfoundland and Labrador, Canada, and was SIRT-IN-1 found to be SIRT-IN-1 closely related ENPEP to viruses circulating in northwestern Europe in the spring of 2021 [31]. Shortly.