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H5N1 Antibodies in Poultry Workers in India
May 11, 2005
>> But virus isolation and sequencing has not been attempted in India, as there is a lack of such a secure bio-safety facility, said Dr A C Mishra, director of the National Institute of Virology, Pune……
Indian researcher Dr Nalini Ramamurthy, director of The King Institute of Preventive Medicine, Chennai said their group chanced upon these three cases of "sero-positivity" in a poultry farm in Kattangalathur, about 45 km south of Chennai, while routinely monitoring the human population for influenza antibodies.
All the three who show positivity have never travelled overseas nor is any poultry imported into India from regions where epidemics have occurred-East Asia-so a native exposure to the virus is the only alternative, she says. <<
The finding of H5N1 antibodies in poultry workers in India is cause for concern. Since the positive serum was collected in 2002, the current situation in India is unknown. Prior to 2002, the only reported human cases of H5N1 infection were in Hong Kong in 1997.
The evolution of H5N1 has been significant since 1997, and the only reported recent cases of infection have been in Vietnam and Thailand, other than low titer antibody detected in Japan in workers who were sanitizing a heavily infected farm in 2004.
More screening for antibody in more recent serum collections from poultry workers would help define the current situation. Isolation and sequencing of the virus would help determine the relationship between the H5N1 in India and the H5N1 elsewhere in Asia.
Detection of virus has become a widespread problem due in part to mismatched primers. Universal primers have not kept pace with the evolving virus, and false negatives have been documented in Vietnam. Unfortunately, these false negatives are probably widespread. WHO consultants have looked at known positives of WSN/33 from Korean pigs and have not been able to confirm the data with their primers. Evolution away from primer sequences such as those listed at the WHO website may be creating detection problems elsewhere as well. Thailand has claimed that there were no human infections of H5N1 this season. However, patients with bird flu symptoms and exposure have been reported to be negative by their PCR test.
Use of lab test to exclude has led to serious undercounts. In southern Vietnam only about 20% of patients with bird flu symptoms and exposures have tested positive for H5N1. These patients have been hospitalized and placed in isolation. Patients with milder symptoms or non-respiratory symptoms are much less likely to have been tested. In northern Vietnam false negatives and non-testing would be a significant concern because milder cases have been documented, suggesting many H5N1 positive patients simply recover at home and are not tested or reported.
The detection of H5N1 in sera collected in 2002 in India suggests the virus is more widespread than previously reported.
Monitoring of H5N1 worldwide is a major cause for concern.
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