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Further Spread of H5N1 across Central Asia

By Eric Toner, M.D., August 30, 2005

Over the past 3 months, highly pathogenic avian influenza virus H5N1 has spread across central Asia, apparently carried by migrating waterfowl. While low pathogenic avian influenza is normally carried worldwide by asymptomatic migratory water birds, this cross-continent spread of a highly pathogenic virus is unprecedented.

On May 4, a die-off of wild geese was discovered at Qinghai Lake, a nature preserve in central China. Approximately 100 days later and 2400 miles to the west, outbreaks were reported in the Ural Mountains of Russia. During this same period, outbreaks also occurred as far north as the northern border of Mongolia and as far south as the Tibetan capital of Lhasa, and there are now unconfirmed reports of outbreaks in the area of the Caspian Sea. These outbreaks have involved both domestic fowl and wild migratory birds. A map on the website of the European Commission provides a clear illustration of the recent spread of avian influenza in Asia, including outbreaks reported from the following areas:

  • 91 villages across 6 regions of Russia

  • 2 villages in the neighboring Pavlodar region of Kazakhstan

  • 2 areas of Xinjiang province of western china

  • Eastern Qinghai Province

  • Southern Tibet

Sequence analysis of the specimens indicates that all of these outbreaks are closely related and appear to have arisen from a strain that was found in southeast China last year.

H5N1 is now on the border of Europe and the Indian subcontinent. As migratory birds carrying the virus move south over the next several months, additional spread is likely, but whether the highly pathogenic virus will move further west is still uncertain. Given that the virus cannot be eradicated from the wild bird population now that it has been established, and that it is being transmitted between species and across disparate locations, continued spread seems likely. As noted in the CBN Bulletin of July 7th, it appears that a pandemic of H5N1 among birds is underway.

The increasingly wide spread of this avian influenza virus is worrisome. Every time a human is exposed, infection is possible, and each time human infection occurs, the virus has an opportunity to adapt to human hosts. As flu season begins in the northern hemisphere over the next few months, opportunities for reassortment between H5N1 and H3N2 strains in a co-infected human will increase. Such reassortment could produce a new virus that is both highly pathogenic and transmissible between humans. To date, no human cases have been confirmed from Central Asia, although rumors of cases persist. However, given the scale of the geographic spread of the virus among migratory birds, it is increasingly possible that a human pandemic could start from a location other than Vietnam or Thailand, making expanded surveillance for human cases of H5N1 crucial.