Prevalence of Avian Influenza Virus in Synanthropic Birds Associated with an Outbreak of Highly Pathogenic Strain EA/AM H5N1

The 2022 - 2023 highly pathogenic avian influenza (HPAI) virus outbreak of H5N1 Eurasian lineage goose/Guangdong clade 2.3.4.4b is the largest in North American history and has significantly impacted wild bird populations and domestic poultry across the United States. Synanthropic birds may play an important role in transmitting the virus laterally to other wild bird species and domestic poultry. Understanding the prevalence of HPAI H5N1 in different avian orders may help inform management decisions and potential risk factors for both wild and domestic bird populations. Following the confirmation of infection of HPAI H5N1 in domestic poultry at two commercial premises in IN, USA, we sampled and tested 266 synanthropic avian species within the Columbiformes and Passeriformes orders and found no detection of the virus at either location. Additionally, laboratories within the National Animal Health Laboratory Network were queried for influenza Type A rRT-PCR assay test results from morbidity and mortality events in wild birds, consisting of 10,786 birds tested across eight orders and 1,666 avian influenza virus detections. Query results were assessed by taxonomic groups for viral prevalence and suggested that the virus most often was observed in predatory and scavenging birds. Although detections were found in non-predatory synanthropic birds including the orders Columbiformes, Galliformes, and Passeriformes, the risk of transmission from and between these groups appears comparatively low, with apparent prevalence rates of 0.0090, 0.0688, and 0.0147, respectively. The highest prevalence was observed in raptors (0.2514), with prevalence rates in exclusively scavenging Cathartidae reaching up to 0.5333. There is strong evidence that consumption of infected tissues is a key pathway for transmission of avian influenza viruses. Understanding the impact of the 2022 - 2023 HPAI outbreak in wild bird populations can provide pertinent information on viral transmission, disease ecology, and risk to humans and agriculture.