- "WHO assumes that the incubation
time for bird flu in humans is 7 to 10 days, longer than that of regular
flu, she said.
- Henry Niman, who runs recombinomics.com,
a Web site tracking the genetics of flu cases, argues that the incubation
period is closer to the two to four days of regular flu, so the boy may
have been infected by another family member, meaning that the virus may
have made three consecutive human-to- human jumps.
- But Cheng said the health agency's "working
hypothesis" was still that it had jumped only twice."
- The WHO working hypothesis on a limited
transmission chain is similar to its investigations of earlier clusters,
which focused on common sources other than humans, leading to a gross underestimate
of the number of cases of human-to-human transmission (H2H) and length
of transmission chains. The clusters in Turkey and Azerbaijan also
involved long transmission chains, but the WHO used tortured arguments
to eliminate H2H, which created faulty data, which then created additional
faulty data such as the 7 to 10 day incubation time.
- The two clusters that WHO linked to
duck blood pudding are good examples. None of the H5N1 positive patients
had the meal within the common 2-4 day incubation period. In the
cluster in Hanoi in 2004/2005, the time between the meal and symptoms was
1 and 17 days. A WHO committee review of H5N1 in the New England Journal
of Medicine stated "The case-to-case intervals in household clusters
have generally been 2 to 5 days, but the upper limit has been 8 to 17 days,
possibly owing to unrecognized exposure to infected animals or environmental
sources". However, this upper limit of 17 days is due to WHO's
efforts to link the brother to the meal, instead of the index case.
The brother developed symptoms when the index case died, which is a common
feature of the familial clusters that involve H2H. Moreover, the use of
7-10 days as indicated above, reduces the number of links in the transmission
- The shorter incubation time of 2-5 days
also explains the 5-10 day gap between the onset date for the index case
and other family members. H5N1 is still not efficiently transmitted
H2H, so transmission peaks several days after disease onset, which when
coupled to the incubation time, creates the 5-10 day gap between the index
case and other family members, which was common in the first 15 clusters
which were documented in an H5N1 familial cluster paper by WHO and the
- These shorter incubation periods not
only support H2H in the smaller cluster of 2 or 3, but also indicate that
the clusters that have long intervals between the first and last member
involve a number of transmission. These long intervals were clearly
present in the larger clusters in Turkey and Azerbaijan.
- However, the current cluster in north
Sumatra is the deadliest. Only one of the eight members has survived,
raising concerns in the changes in the eight H5N1 gene segments.
Those sequences have been sequestered at a private WHO database.
Two sequences from the first confirmed case in Indonesia were released,
but the sequences of the other six gene segments, as well as full sequences
from the other H5N1 cases in Indonesia should be release immediately.
- At least two distinct H5N1 sequences
are co-circulating in Indonesia, creating conditions fro dual infections
and recombination. Therefore the sequences should be available to
the scientific community for detailed analysis.
- © 2006 Recombinomics. All