In the past, only two consistent cases of migratory birds have been recorded, caused by highly pathogenic viruses: in South Africa in 1961 (H5N3) and Hong Kong in winter 2002-03 (H5N1).
In passato sono state registrate solo due consistenti more di uccelli migratori, provocate da virus altamente patogenici: in Sudafrica nel 1961 (H5N3) e a Hong Kong nell’inverno 2002-03 (H5N1).