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2005 H5N1 Vietnam Recombinant Emerged in Hau Giang in 2004
June 30, 2005
The twenty 2005 H5N1 sequences at Los Alamos provide additional clues on the emergence of the latest versions of H5N1 in Vietnam. 10 of the sequences are of HA and all 10 are missing an arginine (ARG) residue within the HA cleavage site. The motif is not new. It was present in sequences from Yunnan, a province in China adjacent to northern Vietnam, as well as isolates in South Korea, Japan, and other locations in China such as Guangdong. These data indicate the 2005 versions circulating in both northern and southern Vietnam in 2005 are recombinants.
However, there is a 2004 isolate (A/chicken/Viet Nam/HauGiang-617/2004(H5N1) from Hau Giang in southern Vietnam which is also missing the ARG, and it's match to the 2005 isolates is even closer than the earlier isolates, indicating the recombinant appeared in Vuetnam in 2004 and was associated in time and location with an outbreak of human cases in northern and southern Vietnam beginning in the middle of July, 2004.
Between the middle of July and early August, there were human cases reported in Hau Giang in the south and Ha Tay in the north. The two cases in the north were young children and both were confirmed to be H5N1 positive. Only one case in the south was confirmed, because no samples were collected on the initial cases. However, the confirmed case in Hau Giang was an older sister of a brother and cousin that died with bird flu symptoms. This familial cluster was unusual in that the brother and cousin developed symptoms at about the same time, while the older sister developed symptoms after her brother died, which is the common bimodal distribution found in virtually all familial clusters in Vietnam and Thailand. The bimodla distribution signals human-to-human transmission.
The sample at GenBank is from a chicken, but was collected from an outbreak that happened at the same time as the human cases. The 10 sequences at Los Alamos indicate that this HA cleave site recombinant spread throughout Vietnam and was present in all 10 2005 H5N1 HA sequences. Thus, the recombinant in 2005 was present in Vietnam in the summer of 2004, and this recombinant emerged as the dominant genotype throughout Vitnam in 2005.
It was associated with human-to-human transmission in the summer of 2004.