H5N1 Transportation and Transmission By Wild Birds
Recombinomics Commentary
September 3, 2007
The Wildlife Conservation Society Field Veterinary Program Director William Karesh is among those attending the meeting in Bangkok.
"We tested thousands of birds in Africa, in Nigeria, in that area, and we cannot find a wild bird with the disease. [That] Does not mean it cannot occasionally get into them, but it is probably not going to go anywhere. It is a dead end," he said.
The above comments are very similar to the statements made in August, 2005 by the same investor representing the same organization. At that time he was investigating the dead wild birds at Erhel Lake in Mongolia. A few months earlier, the Qinghai strain of H5N1 was found in dead wild birds at Qinghai Lake in central China. The die-off of over 5000 wild waterfowl infected with H5N1 was without precedent, because H5N1 frequently produced mild or no symptoms in waterfowl. Sequence analysis identified a new clade, designated clade 2.2 which had a number of novel polymorphisms, including an HA cleavage site of GERRRKKR as well PB2 E627K, which was reported for the first time in H5N1 from a bird. The strains was lethal in experimental chickens, resulting in death within 24 hours. The strain was also fatal in experimental mice. The fnding of the novel strain in long range migratory birds, including bar-headed geese which could fly 1000 miles in 24 hours, was cause for concern.
The outbreak at Erhel demonstrated that the novel Qinghai strain did not burn itself out at Qinghai Lake. Instead, the Qinghai outbreak was followed by infections at Chany Lake in Siberia and adjacent Kazakhstan, as well as outbreaks in remote regions of Mongolia, including Erhel Lake.
Investigators from the Wildlife Conservation Society were helping to collect and test the birds at Erhel Lake. The Qinghai strain of H5N1 was confirmed, but comments from investigators suggested that because of the number of H5N1 positive dead birds was low, and tests of live birds in the area were negative, the infection would dead end.
The predictions of dead end infections in Mongolia, China, and Russia had no real rationale basis. The H5N1 was detected in Russia and Mongolia for the first time, and the match with the Qinghai strain demonstrated that the infection did not die out at Qinghai Lake in May, 2005. The return of Qinghai H5N1 infections a year later in Qinghai Province as well as Siberia and Mongolia in 2006 provided confirmation that the Qinghai strain did not die out in those regions.
However, the H5N1 infections in wild birds in Mongolia and Siberia in the summer of 2005 suggested that H5N1 would spread to Europe, the Middle East, and Africa, as well as south Asia and Korea and Japan because of overlapping flyways. In the following months, all of the above locations, involving more than 50 countries, reported H5N1 infections and in all cases, the H5N1 was the Qinghai strain.
Recently, H5N1 in wild birds in the summer was reported in Germany, France, and the Czech Republic, indicating Qinghai H5N1 was now endemic in wild bird populations in Europe.
Although all of the above outbreaks have been confirmed via isolation and sequencing of H5N1, some groups are still maintaining that the H5N1 in wild birds was died out. These statements are based on assays of live wild birds, which have been shown again and again to produce dismal results. H5N1 was widely detected in Europe in early 2006, yet none of the countries reporting H5N1 in dead or dying wild birds could detect H5N1 in live wild birds. The same was true in Africa, with the exception of the healthy teal in Egypt.
The detection of H5N1 in Egypt in a healthy teal provided insight into the repeated negatives in live birds. Although the teal was PCR H5 positive, efforts to isolate the virus were unsuccessful. The RNA levels were low, so repeated extractions of RNA were required to generate a sequence. The sequence was clearly Qinghai, and was closely related to Qinghai isolates from Austria in 2006. The Egyptian sample was collected in December, 2005, when countries in western Europe and all of Africa claimed that there was no H5N1 in wild or domestic birds.
Thus, the repeated negatives provide little information about the frequency of H5N1 in wild birds. The H5N1 in dead and dying wild birds in the same regions highlights the short-comings of the live bird assays. Other investigators, such as those in Russia, have no problem indentifying H5 sequences or antibodies in live wild birds.
The focus of the conservation groups on assays that have significant sensitivity issues for the Qinghai strain of H5N1 in live wild birds, and the failure of these groups to use more sensitive assays, such as those that measure H5 antibodies, remain causes for concern.
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