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H5N1 Wild Bird Flu Tracking in Mongolia

Recombinomics Commentary

August 13, 2005

Many of the birds that migrate to Qinghai Lake Nature Preserve in China (the site of an H5N1 outbreak in wild birds this spring) also migrate to Mongolia, thus providing a unique opportunity to collect samples from migratory birds for testing for avian influenza.

As noted in the official report to the OIE from the Mongolian government, at least 80 birds died at Erkhel Lake.  At the lake the WCS/Mongolia team counted over 6500 apparently healthy birds of 55 different species.

Over the course of the survey, the team collected samples from 774 individual birds from the 10 sites.  The majority of samples were faecal samples but also included tissues from 4 birds found dead at the site.  Samples came from the following species: Bar-headed goose (_Anser indicus_), Herring Gull (_Larus argentatus_), Black-headed gull (_Larus ridibundus_), Eurasian Widgeon (_Anas penelope_), Ruddy Shelduck (_Tadorna ferruginea_), and Whooper Swans (_Cygnus cygnus_).

The collection of samples from nature reserves in Mongolia is welcome.  The recent migration of H5N1 in long range migrating birds (wild bird flu) has rapidly spread H5N1 along the southern border of Russia and northern border of Kazakhstan (see map).  The initial samples of this expansion came from the Qinghai Lake Nature Reserve in Qinghai Province (red dot on map) in May.  China indicated in their OIE report that 5 species were identified: bar-headed geese (Anser indicus), great black-headed gulls (Larus ichthyaetus), brown-headed gulls (Larus brunnicephalus), ruddy shelducks (Tadorna ferruginea) and great cormorants (Phalacrocorax carbo).

There is some overlap in the species and the sequences of the H5N1 isolated from the birds provide a wealth of information that is considerably more detailed than banding techniques.  At Qinghai Lake, 12 isolates were collected and sequencing shows that the H5N1's are recombinants, with some genetic information from Asia and some from Europe.  Among the European characteristics is a constellation of 3 polymorphisms in the PB2 gene.  This sequence had been previously found in an H3N2 isolate from a child in Hong Kong.  Although the child had not traveled outside of the area, the sequence of the H3N2 was closely related to swine isolates in Europe (H1N1, H1N2, and H3N2).  The bar headed geese from Qinghai Lake provide a mechanism for moving gene fragments from Europe to Hong Kong.  The intermingling at nature reserves provides opportunities for dual infections, which generate new recombinant genes.  These new formed genes contain some genetic information from one source and some from another. It is via this recombination process that H5N1 evolves.

This evolution has created new genes identified in the Qinghai Lake isolates.  These new genes are closely related to genes in Asia, but have evolved away from the isolate from Vietnam used to make the current pandemic vaccine in clinical trials.  Thus, the vaccine under development worldwide will not be effective against the wild bird flu sequences spreading across Asia and heading for Europe.

The H5N1 in these birds is readily isolated because it is so virulent.  It kills experimentally infected chickens in 20 hours and mice in 3-4 days.  The experiments, which determine biologically if the virus is highly pathogenic (HPAI), have been successful at Harbin using samples from Qinghai Lake, Tacheng and Changji in Xinjiang, and Tibet.

Isolates have also been obtained from the Chany Lake region in Novosibirsk (cluster of yellow dots on map).  Preliminary sequence data identifies clear links to the Qinghai Lakes isolates, including an NA gene that is virtually identical, an identical HA cleavage site, and the PB2 polymorphism E627K, which may help account for the virulence and may indicate that isolates will produce neurological effects.  The isolates from Qinghai lake were the first H5N1 bird isolates that had E627K.  Although this polymorphisms is found in all human isolates, all prior H5N1 isolates with the change were only found in H5N1 isolated from mammals (mouse brain, tigers, and humans with poor outcomes in 1997 in Hong Kong, and 2004 in Vietnam and Thailand).

Collection of samples will increase the likelihood of isolating new viruses which can help determine how the H5N1 is being transmitted and how it is evolving via recombination.


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