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H5 Bird Flu in Philippines Low Pathogenic by PCR
July 12, 2005
>> In a routine testing done on samples collected from a small farm in Calumpit, Bulacan province, a low pathogenic H5 avian influenza virus was detected in ducks using hemagglutination inhibition and PCR.
Samples are being sent to the OIE Reference Laboratory for avian influenza in the Australian Animal Health Laboratory, Geelong, Victoria for confirmation of the specific strain involved.
All ducks in the farm are apparently healthy with no mortalities, and all the native chickens in the same farm have tested negative. <<
The above commentary in the OIE report by the Philippines sounds like the H5 detected is not H5N1. The H5N1 isolates in Asia are all HPAI (High Pathogenic Avian Influenza) based on the sequence at the HA cleavage site and or pathogenicity index. Some islolates are missing one ARG and others are missing one LYS, but the cleavage sites are still HPAI. The above report indicates the cleavage site is LPAI (Low Pathogenic Avian Influenza) , which would be more like other H5's in Asia such as the South Korean H5N2 sequence, PQKETK/GLF . LPAI can convert to HPAI, most commonly via non-homologous recombination. Because of the high frequency of H5N1 in Asia, conversion via homologous recombination is also possible.
Since H5N2 is currently being detected in Japan and was previously detected in South Korea and Taiwan, there is a good possibility that the LPAI in the Philippines will be H5N2.
Migratory birds in Asia also LPAI and have various H5 sero-types. However, the migratory birds at Qinghai Lake were HPAI and had a cleave site with a full complement of basic amino acids, matching the prevalent H5N1 cleavage site in Asia.