Human to Human Transmission of Bird Flu Likely - WHO
Recombinomics Commentary
January 21, 2005
>> "I would think it's rather likely that the second one got infected from the first one, because of these nine days difference," Dr. Klaus Stohr said from Geneva.
The older man, 46, died Jan. 10 in Hanoi. Vietnamese authorities only confirmed him as a case of H5N1 on Friday, after a retesting of samples showed proof of infection. He had originally tested negative for the virus.
His brother, 42, remains in hospital but appears to be on the mend.
To date there is no evidence the virus spread beyond the brothers, Stohr said, adding Vietnamese disease investigators looked for but did not find signs of more extensive human transmission.
"There has been no significant increase in respiratory disease in these villages. And that's reassuring."
Sustained transmission over several generations would indicate the virus had undergone genetic changes that allowed it to more easily infect humans - a development that could trigger the pandemic the world's influenza experts have been warning is imminent.
There have been at least four previous cases where limited person-to-person transmission of H5N1 is believed to have occurred, one of which was reported in an article the New England Journal of Medicine rushed to print Friday. <<
The criteria of a caregiver developing symptoms about a week after the index cases developed symptoms or died has been met twice this past summer according to media reports. One was the cluster in Thailand that is most frequently cited. The index case was a 9 year old girl initially diagnosed as dengue fever. Her mother and aunt developed symptoms after the index case died. The mother died and sequence data on recovered H5N1 HA and NA indicated the virus was very similar to earlier isolates in Thailand. The aunt also tested positive for H5N1 and recovered.
In southern Vietnam there was a similar cluster. After a brother and cousin died with bird flu symptoms, the older sister tested positive for H5N1 and died. Sequences of HA and NA from two isolates from chickens who died at about the same time in the same province also were also similar to earlier isolates from Vietnam.
The current situation in northern Vietnam indicates the H5N1 might have changed. Both the index case and brother initially tested as negative for H5N1. The index case was not positive until he was tested a third time. The negative tests may indicate the virus has changed and is now harder to detect. In addition, media reports indicate the 35 year old brother of the two confirmed cases was admitted on January 20. WHO has not yet confirmed the media reports on the third brother. If the third brother is confirmed, he will represent the third generation of human to human transmission since he was admitted 10 days after his 42 year old brother developed symptoms and 19 days after the index case developed symptoms.
There may be difficulties confirming additional cases in the north. A 62M suspect case was reported with the two older brothers, but there have been no reports on confirmation. Earlier, several additional suspect cases were reported, but there have not been reports on their confirmation.
If the virus has changed and is more difficult to detect and is more easily passed from human to human, the number of undetected cases will increase and the likelihood of further genetic change will also increase.
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