Re-emergence of H5N1 in Guangdong Ducks
Recombinomics Commentary
September 17, 2007
Since 2003, H5N1 has re-emerged in Asia with a vengeance, claiming dozens of lives and spreading to Europe, the Middle East and Africa through migrating birds and the poultry trade. Prevention and rapid response when outbreaks occur are therefore extremely important. But no matter how stringent the efforts or affluent the society, the risks of an ever-evolving virus such as H5N1 remain, as has been shown by the several outbreaks among chickens in Japan.
Tests on several wild birds found dead in Hong Kong this year determined that they were carrying H5N1. With initial tests on the ducks in Guangdong pointing to them also having the virus, it is clear that there is a need for defences to be strengthened.
The above comments on the recently confirmed outbreaks of H5N1 on five farms in Guangdong province describe the recent geographical expansion of H5N1 outside of China and regions to the northeast, but the role of trade in this dramatic expansion has no scientific basis.
H5N1 re-emerged in people in late 2003 in northern Vietnam as well as poultry in South Korea and Indonesia. These outbreaks were followed by human cases in Vietnam and Thailand in 2004 as well as China, Indonesia, and Cambodia in 2005. However, Clade 1 in southeast Asia, Clade 2.1 in Indonesia, and Clade 2.3 (Fujian strain) in China and southeast Asia have not been reported in wild birds, poultry, or people in countries to the west of China.
The expansion to the west began in 2005 and followed the report of clade 2.2 (Qinghai strain) in wild birds at Qinghai Lake in May. First reports were in Russia, Kazakhstan, and Mongolia, which were followed by first reports of Asian H5N1 in Europe, the Middle East, and Africa in late 2005 or early 2006. All of these reports of H5N1 in poultry, wild birds, or mammals, including humans, were the Qinghai strain.
Although the other clades and sub-clades were widely detected in China and countries to the east, including initial reports in a goose in Guangdong province in 1996, there is no evidence for these strains in the expanded geographical reach. Clade 1 from Thailand was smuggled into Belgium in 2004, but no Clade 1 cases have been reported in poultry, wild birds, or mammals outside of southeast Asia, other than the two smuggled birds. Similarly, exotic birds in quarantine in the UK in 2006 were positive for Clade 2.3 (Fujian strain), but other than the quarantined birds, no Clade 2.3 has been reported in poultry, wild birds, or mammals outside of China and southeast Asia.
Thus, although multiple clades of Asian H5N1 have been reported in Asia since 1996, no H5N1 was reported to the west of china prior to the Qinghai H5N1 in wild birds in 2005, and all H5N1 isolated since 2005 in countries west of China have been Qinghai, including wild birds in Europe, the Middle East, and Africa.
The H5N1 in Guangdong province will almost certainly be clade 2.3 (Fujian strain) and the emergence of this strain in vaccinated ducks on five farms remains a cause for concern.
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