Recombinomics: Clade 7 Silent Spread Causing Fatal H5N1 Cases in China?

Commentary

Clade 7 Silent Spread Causing Fatal H5N1 Cases in China?
Recombinomics Commentary 17:24
January 18, 2009

Gene sequencing by the National Avian Influenza Reference Laboratory indicated that this virus is very similar to the avian influenza virus variant isolated in Shanxi in 2006.

The above comments are from the OIE report submitted by China for the two H5N1 outbreaks in Jiangsu, China (see updated map). Although 376,998 birds were culled, there were no fatalities listed in the December 26 report because the birds were asymptomatically infected. This raised concerns that similar infections at other farms led to the silent spread of clade 7, which was the clade in Jiangsu as well as Shanxi in 2006 and other poultry outbreaks in areas surrounding Beijing, as well as fecal samples from Hunan in 2006. There were also reports of clade 7 in Vietnam in 2008 prior to the outbreaks in Jiangsu.

The Jiangsu outbreak was followed by the confirmed case (19F) in Beijing, who had purchased and gutted ducks in Hebei and developed symptoms on Dec 24. It is unlikely that these birds had symptoms, and a survey of birds near Beijing failed to identify dead or dying poultry. However, a health care worker in Beijing did develop symptoms, raising concerns of increased efficiency of transmission to humans.

The Beijing case(s) were followed by the fatality in Shandong (27F), who developed symptoms on January 5. The possible exposure has not been disclosed.

These two cases were followed by the case (2F) in Hunan, who is in critical condition in Shanxi. Surveys of markets in Hunan and Shanxi failed to identify dead or dying poultry.

Thus, there has been no linkage of any of the three confirmed H5N1 to dead or dying poultry. However, vaccination of poultry with a poorly matched vaccine would yield asymptomatic birds shedding H5N1 virus, which would facilitate spread in immunized birds that could lead to fatal human infections.

More information on the H5N1 isolated from the three cases this month would be useful.

Clade 7 is readily distinguished from clade 1 or clade 2.1, 2.2, or 2.3, and the distinction can be seen in the HA cleavage site (clade 7 has a G at the third position instead of an R or S).

Media Links