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Fujian H5N1 Bird Flu Spreads Through China and Southeast Asia
April 4, 2006
Recent release of HA sequences from H5N1 infected patients in Anhui and Guangxi provinces in China has focused attention on the sequences previously released from a duck in Fujian Province. The human HA sequences had a cleavage site of RERRRKR, a glycosylation site linked to A158T, changes near the receptor binding domain (P185S and R193K, and a change just upsteam from the HA cleavage site, Q317L. All of these changes were found in the Fujian duck sequences.
2006 H5N1 sequences from Malaysia (Wilayah Persekutan near Kuala Lampur) and Laos (isolated 02/22/06) have been released at Los Alamos and they have the same changes. In addition, the NA sequences of the 2006 isolates have been released, and they are also closely related to the NA sequence from the Fujian duck. The presence of these sequences in Fujian, Anhui, and Guangxi, including all three public human H5N1 sequences from China, and now in the two 2006 isolates from Malaysia and Laos, raise concerns that this sequences is being widely distributed in China and southeast Asia.
The wide distribution and associate with human cases in China is cause for concern. Distribution is likely to be linked to migratory birds and movement into areas which have had human H5N1 cases in the past creates new opportunities for recombination. Changes in the receptor binding domain, S227N in isolates from Hong Kong, sans Fujian Province, and Vietnam raise concerns that the changes near the receptor binding domain make increase efficiencies in transmission to humans. Moreover, one of the human isolates from China has an additional change, Q226R, within the receptor binding domain.
This emerging sequence fro Fujian province is not likely to appreciably cross react with a vaccine directed against the HA H5N1 sequence from Vietnam or Indonesia. Thus, a new pandemic vaccine related to this emerging sequence is warranted. As H5N1 continues to rapidly evolve via recombination, it is necessary to recognize this fundament mechanism of drifts and shifts and to target existing H5N1 for vaccine development and immunization now, before the H5N1 efficiency markedly increases.