Broadened Host Range and Efficient Human Transmission of Evolved H5N1
Recombinomics Commentary
April 30, 2005
>> there is a steadily increasing number of clusters of disease, where it appears to have spread between people. There are now at least seven of these, almost all in the northern province of Haiphong. WHO officials say this is unprecedented.
Finally, the virus itself seems to have changed physically. Vietnamese health experts say that it has evolved in the north of the country by dropping an amino acid.
The US government's Centers for Disease Control and Prevention, which has analysed many of specimens of the virus from Vietnam, adds that new strains of it "are becoming more capable of causing disease for mammals". <<
The comments above suggest that the northern H5N1 not only has been associated with a lower case fatality rate in larger clusters, but the dropped amino acid is also associated with a broader host range.
The confirmation of H5N1 in the family of five in Haiphong signaled the start of the flu pandemic. All five family members were admitted on the same day and all recovered relatively quickly. The recovery in a week or two is similar to a bad case of human flu, suggesting there may be many more unreported cases. The above comments suggest there have been seven clusters in Haiphong alone. The neighbors of the family of five had been admitted to the hospital a few days after the family of five. Although test results were not reported, the above comments suggest these neighbors may represent another cluster in Haiphong.
On April 15 northern Vietnam had sent the CDC a large number of the 1000 samples they had collected from people and animals. The above comments may indicate earlier results, since the clusters in northern Vietnam have been reported since the beginning of the year. Earlier there were also comments about the genetic composition of H5N1 changing, and recently the lost amino acid was acknowledged. The lost amino acid sounds like isolates from China in 2003, which have also lost an amino acid in the polybasic region of HA. It sounds like the new isolates from northern Vietnam are recombinants. The recombined genes are more efficient at infecting mammals, including humans, but this recombination resulted in a reduced case fatality rate.
These changes have striking parallels with the 1918 pandemic which began as a mild infection in the sping of 1918 and evolved into an efficient killer in the fall. The current information coming out of northern Vietnam suggests a similar sequence of events may be happening in 2005, and the flu pandemic has begun as indicated. Moreover, the finding of WSN/33 in swine in Korea suggests the pandemic in 2005 may be beginning on two fronts, with avian viruses becoming more human-like in Vietnam and human viruses becoming more avian-like in Korea. Unfortunately, both sets of viruses can infect birds which could create more mixing and matching of genetic information. This genetic instability could frustrate vaccine efforts based on the last 2004 isolates form Vietnam.
These problems may make the pandemic of 2005 strikingly similar to the pandemic of 1918.
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