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The Emergence and Spread of Qinghai H5N1 Bird Flu
May 9, 2006
Today is the one year anniversary of the report of 189 dead bar headed geese at Qinghai Lake in China. Although H5N1 infection was initially denied, China filed an OIE report on May 21, 2005 indicating that H5N1 was detected in the bar headed geese as well as four additional species of waterfowl, and the number of dead birds was 519. This report was followed by a series of news conferences that quickly raised the total to over 1000 followed by a final number of over 5000 dead birds.
The bird die off at Qinghai Lake was without precedent. Usually wild waterfowl are resistant to H5N1 and the die-off signaled a major change in the transmission of highly pathogenic H5N1 because the dead birds were long range migratory waterfowl. Most of the dead birds were bar headed geese which fly over 1000 miles in 24 hours. Recently H5N1 has again been reported in two counties in Qinghai Province, signaling the completion of one season of H5N1 spread of the Qinghai strain of H5N1.
The Asia strain of H5N1 was first reported in a Guangdong goose in 1996. This report was followed by an outbreak of H5N1 in 1997 in adjacent Hong Kong which infected 18, 6 of whom died. Culling of all poultry in Hong Kong halted reported human cases until 2003, but H5N1 was frequently found in Hong Kong , resulting in repeated culls and signaling H5N1 spread in China.
In 2003 a Hong Kong family that traveled to Fujian Province was infected with H5N1. The isolated virus was similar to the 1997, but quite distinct. The export of H5N1 into a visiting family signaled additional H5N1 in China, but H5N1 was not reported until it exploded into adjacent countries in 2004. Vietnam and Thailand were hardest hit, but H5N1 was also reported in adjacent Cambodia, Laos, and Malaysia as well as Hong Kong, South Korea, Japan, Indonesia, and many provinces in China.
H5N1 had changed again. One version was in southeast Asia (Vietnam, Thailand, Laos, Cambodia, Malaysia), while another version was in South Korea, Japan, Hong Kong China, and Indonesia, although there were also regional differences outside of southeast Asia.
All human cases however were reported in Vietnam and Thailand in 2004. Cambodia also reported human cases in early 2005 and all human isolates were closely related.
The H5N1 isolated at Qinghai Lake was distinct. Although it had many of the features in the east and southeast Asian versions, it also had sequences that had been found in European isolates. In addition Qinghai isolates had a change (PB2 E627K) that had never been reported in H5N1 from birds. All prior H5N1 with this change was from H5N1 from mammals, including humans. It was also found in all human serotypes (H1, H2, H3) isolated from humans.
Thus, the Qinghai strain of H5N1 was easily distinguished from the H5N1 to the east, but its ability to be transported and transmitted over long distances was unclear. Its high lethality may have cause it to burn out at Qinghai Lake. However, the large number of waterfowl that visit Qinghai Lake in the spring discounted this possibility and the Qinghai outbreak in May was followed by reports of fatal H5N1 infections in farm ducks in Xinjiang province, northwest of Qinghai Lake. The fatal infections in domestic waterfowl strongly suggested that the Qinghai strain of H5N1 was migrating towards southern Siberia, where many birds from Qinghai Lake summer. This possibility was confirmed in July when Russia reported H5N1 infections in farms surrounding Chany Lake in southern Siberia (see summary of OIE reports on Qinghai strain of H5N1 bird flu).
The outbreak in Russia was supported by similar reports of H5N1 in region of Kazakhstan adjacent to Chany Lake as well as dead birds at nature reserves in Mongolia, including Erhel Lake. OIE reports out of Russia indicated the H5N1 infections were extensive, covering a series of southern provinces. Sequence data confirmed that the outbreaks in Russia, Kazakhstan, and Mongolia were all due to the Qinghai strain of H5N1. Reports from Russia also indicated that H5N1 was also found in two dozen species of wild birds shot by hunters, indicating H5N1 could be both transmitted and transported by long range migratory birds.
The reports from Russia in August left little doubt that H5N1 would soon be migrating into Europe. Early reports cited H5N1 in the Volga Delta and the intersection of migratory bird flyways in the southern Siberian region of Russia left little doubt that the migration of H5N1 into new areas of Europe, the Middle East, and Africa would happen in the fall and winter.
These predictions were confirmed with reports of H5N1 in Romania, Croatia, and Turkey in the fall. The sequence data again confirmed that the new outbreaks were due to the Qinghai strain. Ukraine also reported H5N1, and these reports raised serious doubts about surveillance in European and Middle East countries which claimed to be H5N1 free.
At the beginning of 2006, human cases were reported in Turkey. These reports were followed by OIE reports from Turkey indicating H5N1 had been widespread in eastern Turkey since mid November. These reports cast further doubt on claims of neighboring countries that they were H5N1 free since the birds in Turkey had passed over many H5N1 countries and had then traveled over the Middle East into Africa.
By the end of January, reports of H5N1 in Europe began to appear and these reports were followed by a flurry of reports in February. Reports of H5N1 in the Middle East and Africa also began to appear and the number of countries reporting H5N1 for the first time was without precedent.
Reporting countries described H5N1 in a large number of wild and domestic species and raised additional surveillance questions about denials from neighboring countries. Human cases were reported in Turkey, Iraq, Azerbaijan, Jordan, and Egypt.
H5N1 is now beginning to migrate back north, out of Africa into western Europe and North America as well as out of eastern Asia into Qinghai Lake. This will be followed by further migration into southern Russian by H5N1 from Asia, India, Africa, and Europe. The interactions at Qinghai Lake in China and Chany Lake in Russia, should lead to significant evolution of H5N1 in the upcoming months, setting the stage for a new round of migrations in the fall.