BackgroundThe epidemiology of avian influenza viruses (AIVs) in gulls is only partially known. The role of the world's most numerous gull species, the black-legged kittiwake (Rissa tridactyla), as a potential AIV reservoir species has been unclear. The prevalence of AIV and humoral response against AIV were therefore studied in a colony of apparently healthy black-legged kittiwakes breeding in a nesting cliff in the South West Barents Region of Norway (70°22' N, 31°10' E), in 2008 and 2009.ResultsAIVs were detected from the oropharynx and cloaca in low amounts, with prevalences of 15% and 5%, in 2008 and 2009, respectively. Direct, partial sequencing of the hemagglutinin (HA) gene revealed that the H4 subtype was present. In 2009, antibodies to influenza A virus were detected in sera from 57 of 80 adult birds. In contrast, none of the three-week-old chicks (n = 18) tested seropositive. Hemagglutination inhibition (HI) assays demonstrated that the adult kittiwakes primarily had antibodies specific to the gull-associated H13 and H16 subtypes, with antibodies to H16 being most common.ConclusionsThese results support that the highly pelagic black-legged kittiwake is a reservoir of AIV. The serological findings suggest that H16 might be the main AIV subtype in the black-legged kittiwake. Further studies are needed to understand the ecology of AIV in the black-legged kittiwake and in gulls in general.

Infectious salmon anaemia (ISA) is a viral disease that was fi rst recorded in 1984 in farmed Atlantic salmon. The infectious salmon anaemia virus (ISAV) is classifi ed as the type species of the genus Isavirus in the Orthomyxoviridae family and is evolutionary remote to the infl uenza viruses. The genome consists of eight negative single-stranded RNA segments, and it utilises the same mechanisms as infl uenza viruses to enter and exit cells. Although a common ancestor of ISAV and other genera of Orthomyxoviruses could be dated back several millions of years, there are still many similarities between ISAV and the infl uenza viruses regarding morphology, replication cycles and interactions with their respective hosts.