Silent spread of H5N1 in Europe’s ducks
FAO has warned that H5N1 silently spread by domestic ducks could become endemic in Europe.
Asia is home to over 80% of the world’s domestic duck population but Germany received the biggest ‘hit’ of the H5N1 highly pathogenic avian influenza virus recorded anywhere in the world. Within two weeks during August and September 2007, 365,000 ducks were culled on three farms. Initial outbreak in the southern state of Bavaria at Wachenroth in the state’s Erlangen-Hoechstadt region was followed by positive blood samples identified in two similarly large flocks at farms nearby.
Disease was first identified in ducklings at Wachenroth on 24 August 2007 following death of 400 birds over a short period subsequently confirmed as the lethal H5N1 sub-type. Bavarian authorities wasted no time and culled the entire flock of 160,000 ducks within 24 hours, reportedly by gassing or electrocution in several large containers.
Suspected source of infection was cereal straw carried into the poultry houses for bedding. Ottmar Fick, chief veterinarian in the Erlangen district of northern Bavaria, said it remained unclear how straw stored on the farm was contaminated although infected wild swans found in Bavaria during July 2007 were possibly the source.
Veterinary officials claimed that the outbreak was probably more widespread and of longer duration than first thought due to ducks carrying H5N1 without showing symptoms of disease. Less than two weeks later, German authorities announced a further 205,000 ducks would be slaughtered at two farms in nearby Bavarian towns of Trumling and Hofing near Schwandorf, east of Nuremburg, after laboratory tests on blood samples indicated exposure to the H5N1 subtype.
Head of Bavaria's state office for health and food safety, Volker Hingst, claimed the cull was a precautionary because the birds were not visibly sick. Such observations are consistent with previous Asian experience of H5N1 in domestic ducks, the so-called ‘silent’ carriers, which carry the virus without showing symptoms. For ultra-cautious Germany, positive blood tests were enough, and culling began on 8 September. It was not immediately clear how the virus arrived at the two farms but they were apparently business subsidiaries of the infected duck farm near Elangen.
Subsequent reports said the H5N1 virus had been found in 18 deep-frozen ducks set aside as batch samples at a poultry-company slaughterhouse, and suggested infected meat may have entered the food chain. H5N1 virus is known to persist almost indefinitely at low temperatures, although Roland Eichorn of the Bavarian consumer affairs ministry was quick to point out that contaminated meat would pose no problems providing it was properly cooked. He did not completely rule out the possibility of infected meat from the Wachenroth butchery reaching shops but said officials moved quickly after first signs of the outbreak, impounding all meat produced at the farms.The most surprising aspect of this outbreak – by far the largest single H5N1 event in Europe and for ducks worldwide – is the relatively small amount of news coverage generated in Germany and Europe in general at the time. In retrospect, it appears it to have been a ‘milestone’ event for H5N1, at least as far as Europe is concerned.