Current status of influenza virus in Dutch coastal seals: Possible threat to animal and human health?
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In this experiment the seroprevalence of antibodies against influenza A virus among seals living in Dutch coastal waters is studied. Over 500 serum samples of seals (harbor seals and grey seals) were tested in a NP-ELISA for the presence of antibodies. The two positive samples, along with 5 other samples displaying a result just above the cut-off value were tested in HAI assays against all common influenza subtypes. This revealed one adult grey seal reacting with a HI titer of 40 against the avian influenza A virus strain A/HerringGull/Netherlands/3/2006 (H4N6) while not showing a HI titer against A/Seal/Massachusetts/47/83 (H4N5), an influenza A virus strain that has been isolated from seals. This indicates infection with a not previously described influenza A/H4 strain in seals. The other positive sample (adult grey seal 2007) stayed undetermined. All sera were screened for antibodies against influenza A/H4 virus in a HAI assay, this revealed no additional positive samples. Infections with influenza A have not been described in grey seals before. The absence of antibodies against influenza A viruses in the vast majority of the seals makes this population very vulnerable for the introduction of a new influenza A virus. Our findings do not indicate a current risk for human health by seal influenza.