As a seasonal precursor to outbreaks of HPAI in commercial flocks, many nations including Japan report isolation of H5 avian influenza from both migratory and domestic wild birds based on the intensity of surveillance.

In their quarterly annual report to the World Organization for Animal Health, Japan documented isolation of H5 avian influenza isolates from wild birds from December 2023 through April 30, 2024.  Forty individual birds were identified as infected, predominately large-billed crows and a peregrine falcon. 

Japan encounters seasonal introduction of HPAI by migratory birds moving either southward in fall or northward in spring migrating to and from Eurasia.  Most of these isolates were characterized as a H5N5 highly pathogenic strain.  This virus circulated in crows that are ubiquitous and due to their feeding habits are likely to transmit infection to commercial poultry if allowed either direct or indirect contact with flocks.

Raptors become infected through consuming prey carrying H5 avian influenza virus. Mortality in falcons suggests the presence of infection in diverse species representing a high risk to poultry flocks.