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Monitoring of Bird Flu with Pandemic Potential
January 6, 2005
>>Eight of the 12 patients had direct exposures to ill poultry 2-8 days before onset. Seven of the 12 were young children, and routine laboratory testing at the time of admission to hospital identified marked lymphopenia in 8. Although the initial chest radiographs would not immediately identify these cases as unusual, deaths in children and younger adults from hospitalized, radiographically confirmed pneumonia typically range from 1% to 10% and from 1%-5% among patients with radiographically confirmed pneumonia in rural Thailand. Thus, the progression in 9 of the 12 patients to ARDS, followed by the death of 8 patients, separates these cases as a form of unusually severe pneumonia.<<
The recent report on missed bird flu case in Thailand at the beginning of 2004 raises questions about monitoring, A new flu season is beginning and new human fatalities have been reported in Vietnam along with H5N1 infections in poultry in Vietnam, Thailand, and Indonesia. Conditions created by the tsunami in Thailand and Indonesia raise additional monitoring concerns.
The recent report focuses on H5N1 confirmed cases in Thailand in early 2004. However, similar missed cases were also reported in Vietnam and Thailand over the summer. In Vietnam there was a case cluster involving a brother, cousin, and older sister. The brother and sister developed bird flu symptoms and died prior to collection of samples for testing for H5N1. The older sister subsequently developed symptoms and she tested positive for H5N1. The family was located in Hau Giang and isolates from infected chickens were closely related to earlier isolates. A similar cluster was also detected in Thailand involving a mother daughter and aunt. The daughter developed bird flu symptoms but was diagnosed as having Dengue Fever and died before samples had been collected. Her mother and aunt subsequently developed bird flu symptoms and tested positive for H5N1. The mother died, but viral RNA was isolated from cadaver tissues and the sequence was closely related to H5N1 from earlier that year. Had the index cases transmitted virus to relatives, the cases would have also probably gone undetected.
A similar situation has developed in Korea. Swine isolates have been sequenced and shown to contain human genes from 1933, The genes are from a popular lab cell line, WSN/33 and have been publicly available for over a month at GenBank. The sequences raise questions on their origin as well as their pandemic potential since the H1N1 isolates have human surface proteins and the virus produces lethal neurotropic infections in mice. These sequences have yet to be publicly acknowledged.
Thus far H5N1 has not been reported to have acquired efficient human to human transmission and there have been no reports of WSN/33 like infections in humans. However, flu season is beginning, and close monitoring of these virus is warranted, including H5N1 in tsunami affected areas.