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Confirmation of Human to Human Transmission of Bird Flu
January 24, 2005
>>The findings appear to be the strongest evidence so far of person-to-person transmission of H5N1 avian flu since the disease became widespread in Southeast Asia last year. But the authors say they found no sign of any further transmission and no evidence of mutations that could enable the H5N1 virus to spread easily among people. Disease experts fear that such mutations could lead to a flu pandemic.<<
The evidence for the published case study of human to human transmission of bird flu in Thailand was strong because the mother was in Bangkok prior to the development of symptoms in her 11 year old daughter. However, the overall circumstances are virtually identical to three other clusters in Vietnam. In each of the other clusters, the caregiver developed symptoms after the index case died. The symptoms were about 10 days after initial symptoms in the index case.
In the cluster in Thailand, sequence data was obtained from the fixed tissues of the mother. The sequences at GenBank are virtually identical to earlier isolates in Thailand, suggesting additional unreported human to human transmissions. Likewise, the sequences of chicken isolates in Hau Giang were virtually identical to earlier sequences from Vietnam, also suggesting additional unreported transmissions.
The current clusters in Vietnam suggest that the efficiency of transmission may have improved. In the Hanoi area, the brothers each developed symptoms about 10 days from the earlier case. Thus, the index case developed symptoms a few days after the meal which included uncooked duck blood. However, the caregiver brother didn't develop symptoms for 10 additional days. He was hospitalized on Jan 13 and his younger brother developed symptoms and was hospitalized on Jan 20. The three generations of human to human transmission are the longest reported series.
The other recent cluster involves an unconfirmed case (22F), who developed symptoms after the 17 year old brother died. She is in critical condition.
The recent cases of human to human transmission appear to be happening at a higher frequency and the ease of transmission reports have been supplemented with fatal cases after swimming or bathing in water containing dead poultry. These cases suggest that infection of humans is becoming more efficient and are cause for concern.