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
journeys.
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.