The cases in western Europe in February 2006 after a cold spell on the Black Sea showed that irus can spread through infected wild birds traelling short distances, but no eidence for long distance transmission during seasonal migration has yet been found.

• 2006年2月春寒过后，在西欧黑海发生的疫情显示，病毒可通过受感染的野生鸟类的短途旅行播撒，但在候鸟的季节性长途迁徙中还未发现证据。