Migration of Qinghai H5N1 Into the Czech Republic
Recombinomics Commentary
June 23, 2007
The most likely way that the virus was transmitted was via the bedding that was used for the flock. It was contaminated by the droppings of wild birds. That's how the virus could have hit a flock that was being held indoors."
According to the latest news, another four wild birds, which were suspicious of bird flu, were found near Litomysl in east of the Czech republic.
The above comments suggest that the H5N1 infection at the turkey farm in the Czech Republic was cause by wild birds. Moreover, the deaths of wild birds in the region are under investigation. Similarly, media reports describe the testing of dead swans in Germany.
The presence of H5N1 in wild birds in the region would not be a surprise. Earlier this year H5N1 was reported in Hungary, and test of dead or dying wild birds last season identified Clade 2.2 Qinghai H5N1 in over 700 birds.
The status of H5N1 in Europe was highlighted this week in the Options for the Control of Influenza VI by Ian Brown, who runs the veterinary lab in Weybridge, England, and Ilaria Capua, who runs the veterinary lab in Padova, Italy.
Both emphasized the reduced detection of H5N1 in wild birds this season. Capua suggested hat the failure to detect H5N1 in wild birds in Europe and Africa indicated the widespread detection in 2006 was due to a transient presence of H5n1 in that population. Brown, acknowledged that the detection in 2006 was in dead or dying wild birds and also provided data showing that most of the positives were in mute swans, and most were in Germany or Austria. He also noted that the winter in 2006 was harsh, and the mute swans likely served a sentries because they were large and deaths were frequently reported.
He also noted that H5N1 in Europe has also been detected in crested hawk-eagles in Belgium in 2004 as well as quarantined exotic birds in 2006. However, these data provided more evidence for the introductions of H5N1 into Europe via wild birds. The H5N1 in the smuggled birds in Belgium was Clade 1 from Thailand. The sequences have been made public, and the isolates clearly are Clade 1 with many regional markers from Thailand. Although smuggling of infected birds from Thailand was likely not limited to the two birds confiscated, Clade 1 H5N1 has never been reported in poultry or wild birds outside of a subset of countries in southeast Asia. Similarly, the phylogenetic tree of the HA from the exotic birds that died in quarantine was Clade 2.3 (Fujian). Although the Fujian strain has spread from China into southeast Asia, it has never been reported outside of eastern or southeastern Asia. Thus, the establishment of H5N1 in wild birds or poultry in Europe is not likely to be linked to smuggling and trade from eastern or southeastern Asia.
In contrast, all H5N1 west of China has been Clade 2.2 (Qinghai) strain. First reported at Qinghai Lake in May, 2005, the strain has spread into Mongolia, Russia, and Kazakhstan in the summer of 2005, and then west into Europe, the Middle East, and Africa in the fall of 2005. This season it also spread into South Korea and Japan. The number of countries reporting Clade 2.2 H5N1 has now grown to approximately 50, and all reported the outbreaks after the initial report from Qinghai Lake. Moreover, the vast majority of the countries have reported HPAI H5N1 infections for the first time.
In many cases, the Qinghai H5N1 has only been reported in wild birds. Although such reports have been lower this season, the reduced levels are tightly linked to surveillance progams that lack sensitivity to detect H5N1 in healthy wild birds. This season many countries are surrounded by H5N1, yet have failed to report any H5N1. This was true of Western Europe in the fall of 2005. Although H5N1 had migrated into the region, as evidenced by H5N1 detection in Romania, western Turkey, and the Nile Delta, no country in Western Europe reported H5N1 until 2006. These detection / reporting failures were also throughout Africa.
Moreover, the subsequent widespread H5N1 detection in early 2006 was limited to dead or dying birds. Only Russia and Egypt have reported isolation of H5N1 from healthy wild birds.
The surveillance shortfalls are cause for concern, especially when the false negatives are used to proclaim wild birds largely free of H5N1, as was done in the Capua presentation.
A more serious and sensitive effort at detecting H5N1 in both health and dead wild birds would be useful. These isolates evolve via recombination, and tracing of polymorphisms are useful for predicting new emerging sub-clades, which are appropriate vaccine targets.
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