LAUSR

Received: 25.10.2017 Accepted: 01.11.2017 Since November 2016, Switzerland is affected by a major outbreak of avian influenza (AI) in wild birds. The Avian Influenza A virus belongs to the family Orthomyxoviridae and is a single stranded, segmented, negative-sense RNA virus. Single point mutations (antigenic drift) occur frequently, and exchange of entire genome segments between two different influenza viruses co-infecting a host cell simultaneously (antigenic shift) may lead to significant changes in virus characteristics and are key factors for onset of new pandemics. Haemagglutinin (HA) and neuraminidase (N) are the two major surface glycoproteins. Highly pathogenic avian influenza (HPAI) viruses contain a multi basic cleavage site within the HA, exhibit an intravenous pathogenicity index > 1.2 in 6-week-old inoculated chickens or cause more than 75% mortality within 10 days in 4 to 6-weekold intravenously inoculated chickens (OIE, 2015). The recent AI strain, HPAI H5N8 2016/17, belongs to clade 2.3.4.4b, which is different from the HPAI H5N8 clade 2.3.4.4a virus, that was introduced into Europe in February 2014, causing outbreaks in commercial chicken holdings in Hungary, Germany, Italy, the Netherlands and the United Kingdom (Verhagen et al., 2015). Clinical symptoms of AI vary from subclinical to severe respiratory or enteric disease depending on the virus strain, the virus pathogenicity and the host. Wild ducks as the natural reservoir usually exhibit no or mild, mostly enteric symptoms. In contrast, HPAI in chickens and turkeys may lead to 100% mortality within a few days (Swayne et al., 2013).