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H5 Spread on South Korean Farms
November 27, 2006
Bird flu was found in a pair of chickens raised in South Korea's southern city of Seosan, north of Iksan where the first outbreak took place and thousands of chickens were subsequently culled, government officials said Monday.
The chickens found to be infected with the deadly epidemic had been born out of eggs supplied from the Iksan poultry farm where the highly-virulent strain of bird flu was discovered last week, the provincial officials said.
The above comments indicate the H5N1 on South Korean farms may have spread. Earlier reports had indicated that the infected farm was on a migratory bird flyway, which would also be true for the second farm, which is near the western coast of the South Korean peninsula. Both high and low path H5 is spread by migratory birds.
The time and location of the first outbreak suggest the H5N1 is being spread by migratory birds. The last confirmed outbreak of H5N1 in Korea was in December, 2003. That outbreak was quickly followed by H5N1 in Japan in early 2004. H5N1 from both countries was very similar and the H5N1 in Japan was found in wild birds.
The sequences from Korea and Japan in 2003/2004 were subsequently found in dead waterfowl at Qinghai Lake in the spring of 2005, further linking H5N1 in Korea and Japan to long range migratory birds. These birds were the likely source of the H5N1 outbreaks that exploded in Asia in 2004.
At that time, there was little sequence data on wild birds, but the H5N1 in Hong Kong in 2002 and 2003 had many polymorphisms that were not in H5N1 isolates from 2001, indicating the new polymorphisms had flown into the region.
The Qinghai outbreak provide clear data for the transport and transmission of H5N1 because the Qinghai isolates had the novel HA cleavage site of GERRRRKKR as well as PB2 E627K. Moreover, the strain could killed wild and domestic waterfowl, which created a trail of dead and dying birds along the migration routes.
Prior to the Qinghai outbreak, the Asian strain of H5N1 had not been detected west of China. The newly introduced H5N1 into Russia, Kazakhstan, Mongolia, India, Afghanistan, and countries throughout Europe, the Middle East, and Africa were all infected with the Qinghai strain of H5N1 in 2005/2006
Detection of the Qinghai strain in eastern Asia has been limited. Although over 700 Qinghai H5N1 infections were identified in Europe, only one Qinghai isolate has been reported in eastern Asia (Shantou in 2006). However, this detection failure is likely to be due to surveillance issues, which have been largely limited to feces from live markets in southern China.
More aggressive testing of dead or dying waterfowl would be useful. Most H5N1 detected in Europe have been from dead wild birds. Detection in live birds is rare, unless the level of H5N1 in the area is high, such as the detection of H5N1 in wild birds in Siberia after widespread detection in dead or dying poultry on farms.
Surveillance of H5N1 remains poor worldwide. These failures are largely due to efforts focused on testing live wild birds, and active avoidance of dead or dying birds. In the United States, approximately 35,000 live of hunter killed birds have been tested this year, while the number of dead or dying birds is less than 1000 throughout the country, including Alaska and Hawaii. Although low path H5N1 has been detected in the live birds collected over a wide area, there has been no H5N1 reported in dead or dying birds from the same areas, indicating the collection and testing experimental design is fatally flawed.
Thus, more outbreaks on farms form migratory birds are expected to occur without warning, because the surveillance methods worldwide have largely failed.
More details on the age of the infected chickens, as well as sequence data on the bird flu detected in both locations would be useful.