Martin W

    First wild bird cases of avian influenza in European Union
    BirdLife news release

    Three swans and a wild goose in Greece, up to 22 dead swans in southern
    Italy and Sicily, and a swan in Slovenia have died of avian influenza.
    Five of the Italian birds have tested positive for the deadly strain of
    the H5N1 virus that originated in poultry and has been circulating
    widely within Asia for the last decade. Bulgaria is expected to announce
    its first cases of the virus soon in infected geese.

    This is another worrying development in the spread of avian influenza
    following the virus’s appearance, last week, in Nigeria. Unlike the
    African outbreak, however, which is restricted to poultry and was linked
    by the government to the illegal import of infected chickens, the
    European outbreaks involve wild birds.

    All the swans are believed to be Mute Swans Cygnus olor, a species that
    visits southern Italy and Greece from the Black Sea region. Their
    movement into southern Europe is likely to be in response to freezing
    weather conditions around the Black Sea.

    In outbreaks of H5N1 so far, wild birds normally die within a few days
    of infection. The appearance of the swans in Italy, Slovenia and Greece
    indicates they were likely infected just prior to setting off on their

    It is possible the swans caught the disease from other wild birds,
    although this is unlikely given the tens of thousands of waterfowl that
    have tested negative for H5N1 over the last decade. A more likely route
    is through contact with infected poultry or their faeces. Mute Swans,
    like wild geese but unlike most ducks, often feed by grazing on
    agricultural fields.
    The practice of spreading poultry manure onto
    fields as fertiliser is widespread in many parts of Eastern Europe, and
    this is a possible source of infection. The United Nations Food and
    Agriculture Organisation (FAO) has warned “Viruses can stay alive in the
    manure for many weeks. If the manure is spread too quickly in the
    fields, the virus may contaminate poultry.” The swan deaths highlight
    the need for implementation of strict biosecurity measures in infected
    areas, and also highlight the need for monitoring of healthy wild birds
    for the presence of the virus.

    Swans seem particularly susceptible to H5N1 avian influenza, and Mute
    Swan deaths have previously been reported in Russia and in October 2005
    in Croatia. Tests on the Croatian swans found the birds excreted tiny
    amounts of the virus. Even so, it was remarkable that waterbirds sharing
    the same fish ponds as infected swans remained free of the disease.

    The finding of dead swans will fuel the debate over how H5N1 is
    spreading. However, if wild birds had been spreading the disease across
    continents there would have been trails of dead birds following
    migration routes, which isn’t the case.

    The “wild bird” theory for the
    spread of H5N1 provides no explanation as to why certain countries on
    flight paths of birds from Asia remain flu-free, whilst their neighbours
    suffer repeated infections, nor of why only a single strain of H5N1 is
    found in outbreaks west of China.