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Vietnam Reports 304 H5N1 Outbreaks
December 2, 2005
Vietnam's latest OIE filing details 304 H5N1 outbreaks. The vast majority of these outbreaks began in the last week in October or in November. The outbreaks were primarily in northern Vietnam and had the following distribution:
Bac Giang (13), Bac Lieu (1), Bac Ninh (22), Cao Bang (3), Dong Thap (8), Ha Giang (1), Ha Noi (1), Hai Duong (42), Hai Phong (1), Hoa Binh (1), Hung Yen (5), Nghe An (8), Ninh Binh (31), Phu Tho (1), Quang Ninh (7), Son La (18), Thai Bonh (1), Thai Nguyen (3), Thanh Hoa (47), TP-Hai Phong (87), Vinh Phuc (3).
It is unclear if these are linked to migratory birds, but the isolates from Qinghai Lake were HPAI H5N1 and all had the PB2 polymorphism E627K, which is associated with increased virulence in mammals. Earlier this year the outbreaks in northern Vietnam were milder, but clusters were more common and larger. The outbreaks were associated with a recombinant H5N1 that had dropped an R in the HA cleavage site.
Sequence data from the recent outbreaks would be useful. All indigenous H5N1 sequences in Vietnam since 2004 have been amantadine resistant, while none of the H5N1 wild bird sequences have had mutations in the M2 ion channel, the target of the amantadines. Moreover, all of the H5N1 wild bird sequences at Qinghai Lake had the missing R and had a cleavage site of RRRKKR, matching the 1996 Guangdong goose sequence.
The mixing of the two HPAI H5N1 sequences could create new problems and may be reflected in recent concerns about increase human-to-human transmission of H5N1 in Vietnam, Thailand, Indonesia, and China.