Seasonal Dynamics of Avian Influenza Viruses in Ring-billed Gulls (Larus delawarensis) in Minnesota

Abstract

Birds within the orders Charadriiformes (shorebirds; gulls) and Anseriformes (waterfowl) are reservoir hosts for low pathogenicity avian influenza viruses (LPAIVs), but their role in the transmission dynamics of highly pathogenic avian influenza viruses (HPAIVs) is unclear. The novel reassortant HPAIV H5N2 that emerged in Minnesota in 2015 was devastating to the poultry industry, resulting in significant financial losses and destruction of millions of domestic poultry. To date, waterfowl have been the predominant focal species for most AIV surveillance and epidemiological studies, yet gulls, in particular, are documented to harbor reassortant AIVs of both North American and Eurasian lineages and are underrepresented in North American surveillance efforts. To address this gap in surveillance, 1346 ring-billed gulls (Larus delawarensis) were sampled during spring and fall migrations and at three breeding sites in 2017 across Minnesota. We found significant seasonal, spatial, and age-cohort dynamics in AIV apparent prevalence within ring-billed gulls in Minnesota. The highest apparent prevalence estimate was 68.36% for juvenile gulls during the Fall migration period. Each season immunologically naïve juveniles consistently had the highest prevalence. Spatial heterogeneity was detected at nesting colony sites; St. Louis County exhibited low prevalence estimates in both adults (0.0%) and juveniles (7.02%), whereas Cass County exhibited the highest prevalence in adults (3.54%) and juveniles (73.07%). No HPAIVs were detected in our sampling efforts, but the high prevalence of LPAIVs, particularly in immunologically naïve birds and all age-cohorts in Fall 2017 warrant further targeted surveillance efforts of ring-billed gulls and other closely related species. Identification of the prevalence of LPAIV H5 and H7 viruses is the highest priority for future research as these variants have the greatest potential for mutating into highly pathogenic forms in poultry.