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Neurotropic H5N1 in Japan Duck Meat Imported from Shandong
June 27, 2005
>> An H5N1 influenza A virus was isolated from duck meat processed for human consumption, imported to Japan from Shandong Province, China in 2003. This virus was antigenically different from other H5 viruses, including the Hong Kong H5N1 viruses isolated from humans in 1997 and 2003.
This duck meat isolate was highly pathogenic to chickens upon intravenous or intranasal inoculation, replicated well in the lungs of mice and spread to the brain, but was not as pathogenic in mice as H5N1 human isolates
However, viruses isolated from the brain of mice previously infected with the virus were substantially more pathogenic
We found that the genotype of Dk/Yokohama/aq10/03 was unique and distinct from any of the H5N1 virus genotypes previously reported, including a recent isolate in Japan
the PB2 gene was closely related to a Dutch H7N7 human isolate (A/Netherlands/1/2003), which was transmitted directly from a chicken. Similarly, the PA gene was most closely related to a A/chicken/Shantou/4231/2004 strain and to a recent H5N1 isolate from Japan, and the NP gene most closely related to an H3N8 isolate from an aquatic bird (A/aquatic bird/Hong Kong/399/99)
These results indicate that an H5N1 virus with a novel, previously unreported genotype was circulating in China. <<
The above comments are from an ahead of print version of a Virology paper describing the isolation of H5N1 from duck meat imported into Japan from Shandong Province in 2003. This is similar to isolation of H5N1 in 2001 from duck meat imported into South Korea from Shanghai. In both instances several closely related H5N1 isolates were found during routine screening of imported duck meat.
In both instances the isolate virus was a unique reassortant with homologies to other H5N1 in most genes. The Yokahama isolate described above had many biological properties associated with disease in humans, including the ability to replicate in mice without adoptation, as well as containing variants that could be isolated from mouse brain.
In the report above as well as the isolate in Korea, the virus was isolated from duck meat, suggesting H5N1 was in asymptomatic ducks. These data suggest many versions of H5N1 are circulating in China. Neither of the duck meat isolates were the Z genotype. The NA of the recent isolate did not have the 20 aa deletion found in Z genotype isolates as well as the 2001 isolate in Korea. Instead, the NA was like the Z* genotype from the two Hong Kong patients in 2003.
Infections by H5N1 were not reported by China in 2001 or 2003, further suggesting H5N1 is widespread and diverse in China, providing a large gene pool for further recombination. Moreover, presence in asynptomatic ducks would suggest asymptomatic waterfowl could silently transmit H5N1 bird flu throughout Asia, bringing in new sequences and new problems each season.
These data also highlight the unusual lethality of H5N1 in waterfowl in Qingahi and Xinjiang provinces, which are cause for concern.