Commentary
H5N1 Clade 7 Cases in China Raise Concerns
Recombinomics Commentary 19:20
February 5, 2009
But it is slightly different from what we have discovered last year in our market and the outbreak in our local farm in December, which is clade 2.3.4.
On the eight human infections of avian flu in the Mainland, we do not have the full report yet. But according to the preliminary information that is given to us, it is similar to the various virus that was isolated in northern China in the last one or two years.
The above comments from today’s press conference on the H5N1 confirmed birds in Hong Kong strongly suggest that the human cases in China (see updated map) are due to clade 7.
Hong Kong regularly has wild bird outbreaks at this time of the year, and this year, like last year is clade 2.3.2. This sub-clade was also in long range migratory birds in Japan and related sequences were also reported in Korea and southeastern Russia last spring.
Human cases in China have been almost exclusively linked to clade 2.3.4, which is closely related to clade 2.3.2 and both are derivatives of the Fujian strain, which is widespread in southern China.
The only other reported human case in China was clade 7, which was the first confirmed case in the mainland from a fatal infection in Beijing in 2003. Clade 7 was also involved in a series of poultry outbreaks in northern China in the 2005/2006. These outbreaks were difficult to control and required use of multiple vaccines.
More recently, the outbreak in Jiangsu in December was also hard to control and was also clade 7. New vaccinations followed that outbreak, which China reported as asymptomatic.
However, some media reports indicated poultry had died, but was still shipped to market. Shortly after these reports the fatal infection in Beijing developed symptoms, as did the mother of the child (3F) who recovered from an H5N1 confirmed infection.
Clade 7 has been reported in areas adjacent to Beijing, although last year it was also found in Vietnam, and the WHO clade 7 vaccine target is a 2008 isolate from Vietnam.
Published sequences from clade 7 from Shanxi or Hunan has a number of receptor binding domain changes flanking position 190, which is also true of the Tamiflu resistant H1N1 spreading through Asia and the northern hemisphere. These changes allow for escape of the virus from host immune responses as well as vaccines. Thus, both H1N1 and clade 7 H5N1 have created vaccine resistance issues.
Confirmation of clade 7 in the human cases would be useful. This clade will have limited cross reactivity with current pandemic vaccines directed against clade 1 or clade 2.
Release of sequences from the outbreaks in Jiangsu, as well as the recent human cases in China and Vietnam would be useful.
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