Avian influenza overview March - April 2023

Area of Science:

• Veterinary Virology
• Epidemiology
• One Health

Background:

• Highly pathogenic avian influenza (HPAI) A(H5Nx) virus, clade 2.3.4.4b, has been circulating globally.
• Previous outbreaks in Europe showed significant poultry and wild bird involvement.
• Understanding the current epidemiological trends and host range is crucial for risk assessment.

Purpose of the Study:

• To summarize and analyze HPAI A(H5Nx) virus outbreaks in Europe between March and April 2023.
• To assess changes in outbreak frequency and presentation compared to previous periods.
• To evaluate the expanding geographical distribution and host range, including mammalian infections and human cases.

Main Methods:

• Retrospective analysis of reported HPAI A(H5Nx) outbreaks in domestic and wild birds across 24 European countries.
• Comparison of outbreak data with previous reporting periods and the spring of 2022.
• Review of HPAI virus detections in mammalian species and human infections globally.

Main Results:

• 106 domestic and 610 wild bird outbreaks were reported in Europe.
• Poultry outbreaks decreased compared to previous periods and spring 2022, often presenting atypically with low mortality.
• Wild birds, particularly black-headed gulls and threatened species, remained heavily affected. HPAI A(H5N1) expanded in the Americas with new mammal infections. Two human A(H5N1) and four other avian influenza human infections were reported globally.

Conclusions:

• While European poultry outbreaks decreased, the ongoing epidemic in wild birds poses a persistent risk, especially with the dispersal of young birds.
• The virus's expansion into new mammalian hosts in the Americas highlights its evolving host tropism.
• The risk to the general EU/EEA population remains low, but is low to moderate for occupationally exposed individuals.