H5 in Asymtomatic Birds in Bavaria
Recombinomics Commentary
September 17, 2007
Straw contaminated with the H5N1 strain of bird flu was the likely source of an outbreak of the disease at a poultry farm in southern Germany that resulted in 160,000 birds being slaughtered, an official said Monday.
Ottmar Fick, the chief veterinarian in the Erlangen district of northern Bavaria, said it remained unclear how the straw, which was stored on the farm, became infected, although wild birds were a possible source.
German authorities said Friday that more than 200,000 ducks would be slaughtered at two farms in Bavaria after tests indicated the presence of the H5N1 strain of bird flu.
The head of Bavaria's state office for health and food safety, Volker Hingst, said the slaughter was "a purely precautionary measure," taken after "laboratory indications of H5N1" were found. The birds were not visibly sick, he said.
The two farms are located near Schwandorf, east of Nuremberg, and have a total of 205,000 ducks. It was not immediately clear how the virus might have gotten there.
However tests of the Friedrich Loeffler Institute would have resulted in that it acts with the found viruses around completely different strain than in Erlangen.
The above reports describe three geographically and/or genetically distinct H5 outbreaks on Bavaria. The initial report involved highly pathogenic H5N1 that was first noted in dead or dying ducks. Those positives led to additional testing at farms that had commercial ties to the initial outbreak. High path H5N1 and antibodies was found there in ducks that were not visibly sick. Those positives were followed by additional testing at additional farms, where low path H5 was detected. As expected, the low path H5 was genetically distinct from the high path (Qinghai) H5N1 found earlier at the other Bavarian locations.
H5 in Europe has been circulating for some time. Usually it does not produce significant mortality in waterfowl. In contrast, Qinghai H5N1 can produce significant mortality, as seen in the initial outbreak, as well as dead or dying wild birds throughout Europe. In 2006, Germany had over 300 confirmed cases of Qinghai H5N1 in wild birds, which was followed by a similar number in central and southern Germany this year.
However, Qinghai H5N1 does not always produce fatal disease in waterfowl. The outbreak at Qinghai Lake in May, 2005 was followed by an outbreak in and around Chany Lake in July, 2005. The Russian outbreaks also involved the Qinghai strain, which was isolated from a healthy crested grebe. Sequence of all eight gene segments had the characteristic Qinghai markers and was very similar to H5N1 from wild bird and poultry outbreaks in Russia and neighboring regions in Kazakhstan.
Similarly, Qinghai H5N1 sequences were detected in a healthy teal in the Nile Delta in December, 2005. Although the PCR positive sample failed to yield H5N1 virus, repeated RNA extractions led to HA and NA sequences which were clearly Qinghai and most closely related to H5N1 isolated from an asymptomatic cat in Austria in early 2006.
Moreover, H5 antibodies have been routinely detected in wild birds in Russia in 2005, 2006, and 2007, providing additional evidence for non-fatal Qinghai H5N1 infections in wild birds.
The above findings create significant sensitivity issues in surveillance programs world-wide. Many of these programs focus on H5 detection in swabs from healthy wild birds. These programs have failed to detect Qinghai H5N1 in regions where Qinghai H5N1 virus is isolated form dead or dying wild birds, indicating these assays do not have the sensitivity to detect H5N1 in healthy wild birds. Extensive testing of captive birds can yield positives by PCR, but detection of H5 antibodies is more common, and such assays are actively avoided in most of the surveillance programs.
Thus, the recent results from Germany demonstrates widespread H5 infections in domestic waterfowl in Germany, suggesting widespread H5 in wild birds which is largely missed by H5 PCR tests on live wild birds. The testing of the live birds should include tests for H5 antibodies, which signal the presence and spread of low and high path H5 in wild birds.
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