Saturday, January 29, 2011

EID Journal: H5N1 Branching Out

 

 

 

# 5268

 

 

From the CDC’s EID journal we’ve a dispatch describing a new clade of the H5N1 virus discovered among wild birds at Gengahai Lake in Qinghai, China.

 

Gengahai Lake is located some 90 Km from Qinghai Lake, the scene of the massive die-off of birds from H5N1 in May of 2005.

 

 Qinghai Lake

First the link and abstract, then a little discussion.

 

New Avian Influenza Virus (H5N1) in Wild Birds, Qinghai, China

Yanbing Li, Liling Liu, Yi Zhang, Zhenhua Duan, Guobin Tian, Xianying Zeng, Jianzhong Shi, Licheng Zhang, and Hualan Chen 

Abstract


Highly pathogenic avian influenza virus (H5N1) (QH09) was isolated from dead wild birds (3 species) in Qinghai, China, during May–June 2009. Phylogenetic and antigenic analyses showed that QH09 was clearly distinguishable from classical clade 2.2 viruses and belonged to clade 2.3.2.

 

 

In the relatively short history of the H5N1 bird flu virus, the huge bird die off in 2005 at Qinghai lake was a watershed moment. Up until then, the H5N1 virus had been pretty much limited to southeast Asia; Hong Kong, Vietnam, Thailand, Laos, and China.

 

But suddenly, and unexpectedly, we learned that waterfowl (brown headed gulls, cormorants, ducks, geese, etc.) – species that normally carry avian flu viruses with little ill effect – had died by the thousands at Qinghai lake.

 

Something had obviously changed with the virus.

 

As flu viruses mutate, new strains are continually produced that are either `biologically competitive’ and go on to spread, or are not, and quickly fade away.

 

When one of these competitive strains diverges enough genetically from its ancestors, it is designated as being a new `clade’ of the virus.

 

Essentially a new branch on the virus’s phylogenetic tree.

 

What emerged at Qinghai Lake was clade 2.2 of the H5N1 virus.

 

And over the next 18 months, this new clade managed to spread widely – likely on the wings of migratory birds -  across Asia, and into Europe and Africa.

 

Other clades have appeared, and have staked out claims on their own territories across the globe.

 

Clades 2.1.1, 2.1.2. and 2.1.3 for instance, are very common in Indonesia while 2.2.1 and 2.2 are often to be found in Egypt.

 

There are now more than a dozen identified clades, although some of them were temporarily blips, and are no longer seen in the wild.  You can see the evolution of the virus over the years in the graphic below.

 

image

For more on this evolution see Variations On A Bird Flu Theme.

 

What researchers have discovered at Gengahai Lake, 4 years after the original outbreak of clade 2.2, is a new clade (2.3.2) – not seen before in migratory birds in Qinghai.

 

Some excerpts from the discussion (but follow the link to read the whole paper):

 

Our results indicated that QH09 virus is a reassortant containing 7 gene segments of clade 2.3.2 viruses detected in wild birds and the PA gene of CK/Yamaguchi/7/04-like virus, which contributed the PA gene to 1 QH05 virus

 

<SNIP>

 

Similar genotypes of QH09-like clade 2.3.2 viruses were also detected in great-crested grebes and black-headed gulls in Russia in 2009 (12). Bar-headed geese, whooper swans, and other anseriforme birds in Mongolia were infected with QH09-like clade 2.3.2 viruses (13).

 

Therefore, QH09-like clade 2.3.2 virus is likely adapted to wild birds and is similar to clade 2.2 viruses, and its presence in Qinghai suggests that wild birds have spread this virus to other regions.

<SNIP>

 

Qinghai Lake is located near multiple avian flyways. Although there are no reports of detection of clade 2.3.2 virus in wild birds near Qinghai Lake, the finding of clade 2.3.2 virus in the Gengahai wetlands of Qinghai increases concerns about a potential pandemic and the likelihood that avian influenza virus (H5N1) will again spread and increase its genetic diversity.

 

Therefore, determining movements of wild migratory waterfowl from Qinghai Lake and their virologic status is needed to assess potential avian vectors of HPAI virus (H5N1).

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