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Stable H5N1 Bird Flu Sequences in Thailand and Vietnam
December 31, 2004
The sequences of HA and NA from an isolate, A/tiger/Thailand/CU-T3/2004(H5N1), from one of the tigers from the Sri Racha Tiger Zoo have been available at GenBank. Both genes are closely related to other H5N1 sequences from Thailand, including the isolates from a leopard, A/leopard/Suphanburi/Thailand/Leo-1/04(H5N1), and tiger, A/tiger/Suphanburi/Thailand/Ti-1/04(H5N1). The two cats died on January 27 at nearby Khao Khew Zoo.
The close homology suggests that there was little change in H5N1 in Thailand between the beginning of the year and the summer, further demonstrating that the fidelity of replication is quite high and the major changes happen when new sequences arrive for a new season. The HA from the Sri Racha isolate was virtually identical to a chicken isolate, A/chicken/Ayutthaya/Thailand/CU-23/04(H5N1), from Ayutthaya, north of Bangkok.
The high conservation of sequences between the beginning of the year and the summer was also seen in isolates from Hau Giang in the Mekong Delta area in Vietnam. Although H5N1 has become endemic to both areas, the isolates in Thailand remain closely related to earlier Thai isolates while the isolates from Vietnam maintain close homology to earlier Vietnam isolates. The Thai and Vietnamese isolates are closest to each other, and have many polymorphisms in common which are not found in other H5N1 isolates, but are present in mammalian isolates.