Avian influenza is a viral disease affecting both wild and domestic birds. Over the past years, we have regularly heard and read news about cases and outbreaks of varying sizes. Unfortunately, this year is no exception, as both poultry and waterfowl keepers, as well as conservationists, are closely monitoring events in recent weeks with great concern. In early November, infections appeared in Hajdú-Bihar and later in Szabolcs-Szatmár-Bereg counties, spreading to other areas of the Great Hungarian Plain, including the famous migration site, Hortobágy, and the Southern Great Plain. The virus has now begun to decimate the birds resting here during the peak of crane migration. But what exactly is this deadly disease threatening birds?