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Fujian H5N1 In Thailand
August 16, 2006
The strain has a genetic character close to that of the virus in southern China, he said, adding that virologists were still unsure how it crossed the border from there into Thailand.
There are four types of the H5N1 virus in the region _ the so-called Thai-Vietnamese type, the Indonesian type, and another two types occurring in China. The Thai-Vietnamese type has plagued Thailand since official confirmation of the first outbreak in early 2004.
The above comments almost certainly indicate the “new” H5N1 in Thailand is the Fujian strain, first reported in a duck in Fujian province in 2005. That H5N1 had a novel HA cleavage site. The most common cleavage site in Asian H5N1 is PQRERRRKKR. Many H5N1 isolates from China are missing a K to give a cleavage site of PQRERRRK_R. This cleavage site has been seen in Korea, Japan, and China. However, the Fujian stain has another change just upstream from the cleavage site to give PLRERRRKKR. This cleavage site was in all reported human cases in 2005 and 2006 from China.
The reported Fujian infections became more widespread in early 2006. Scientist from the University of Hong Kong placed two Fujian sequences on deposit at Los Alamos. Both were from birds, but they were from Laos and Malaysia, indicating the H5N1 Fujian strain from China was becoming more widespread. After the release of the sequences, Thailand acknowledge the infection, but insisted that only one farm was involved. Malaysia has not acknowledge the H5N1.
At about the same time H5N1 was detected in wild birds in the Hong Kong area. The description of the sequences sounded like the Fujian strain. Recently, the sequences were made public and all were the Fujian strain with the novel cleavage site.
The widespread reporting of the Fujian strain earlier this year strongly suggested that more reports would appear in southeast Asia. This possibility was bolstered by the appearance of Fujian polymorphism in H5N1 from Indonesia. Human H5N1 sequences from Indonesia were recently released. Like the initial H5N1 from July of 2005, the isolates had an Indonesian genetic background with polymorphisms from Thailand, Vietnam, and both strains from China, Qinghai and Fujian. Thus it was clear that H5N1 in Indonesia was acquiring these neighboring polymorphisms via recombination.
Thus, the acknowledgement of two distinct strains in Thailand is not a surprise. The Fujian strain is also a likely cause of the recent outbreaks in neighboring Laos, Cambodia, and Vietnam.
The human infections in China and Thailand suggest there are unreported infections throughout southeast Asia. The Fujian strain is from Clade 2 while the early H5N1 in southeast Asia is Clade 1. These differences may generate false negatives in the many people hospitalized with bird flu symptoms.
Recently China reported a new fatal case in Xinjiang province. The confirmation of H5N1 took 2 months and false negatives were generated by regional testing. These negatives raise concerns that monitoring of human cases throughout Asia and beyond remains scandalously poor, more than two years after the outbreaks of H5N1 in people and poultry beginning in late 2003.
Similarly, the failure to test patients with bird flu symptoms in areas were poultry is dying is also cause for concern, as noted in the recent Garut cluster in Indonesia. Although a genetic link between poultry and people in most reported cases in Indonesia has not been established, the outbreaks in poultry correlate with outbreaks in people.
More comprehensive testing of people and animal reservoirs in Asia is long overdue.