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Human influenza A H5N1 virus related to a highly pathogenic avian influenza virus
E C Claas1, A D Osterhaus, R van Beek
1Department of Virology and WHO National Influenza Centre, Erasmus University, Rotterdam, The Netherlands. Claas@viro.fgg.eur.nl
Background:
In May, 1997, a 3-year-old boy in Hong Kong was admitted to the hospital and subsequently died from influenza pneumonia, acute respiratory distress syndrome, Reye's syndrome, multiorgan failure, and disseminated intravascular coagulation. An influenza A H5N1 virus was isolated from a tracheal aspirate of the boy. Preceding this incident, avian influenza outbreaks of high mortality were reported from three chicken farms in Hong Kong, and the virus involved was also found to be of the H5 subtype.
Methods:
We carried out an antigenic and molecular comparison of the influenza A H5N1 virus isolated from the boy with one of the viruses isolated from outbreaks of avian influenza by haemagglutination-inhibition and neuraminidase-inhibition assays and nucleotide sequence analysis.
Findings:
Differences were observed in the antigenic reactivities of the viruses by the haemagglutination-inhibition assay. However, nucleotide sequence analysis of all gene segments revealed that the human virus A/Hong Kong/156/97 was genetically closely related to the avian A/chicken/Hong Kong/258/97.
Interpretation:
Although direct contact between the sick child and affected chickens has not been established, our results suggest transmission of the virus from infected chickens to the child without another intermediate mammalian host acting as a "mixing vessel". This event illustrates the importance of intensive global influenza surveillance.
Insights
A child died from avian influenza A H5N1, suggesting direct transmission from chickens. This highlights the need for global influenza surveillance to prevent future zoonotic events.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- A fatal case of avian influenza A (H5N1) in a child occurred in Hong Kong in 1997.
- The child presented with severe pneumonia and multiorgan failure.
- Concurrent outbreaks of highly pathogenic H5N1 avian influenza were occurring in local poultry farms.
Observation:
- An influenza A H5N1 virus was isolated from the child's respiratory tract.
- The isolated human virus was antigenically and genetically compared to viruses from avian outbreaks.
- Haemagglutination-inhibition assays showed antigenic differences, but nucleotide sequencing revealed close genetic relation.
Findings:
- The human H5N1 virus was genetically closely related to an avian H5N1 strain from a local chicken farm.
- Antigenic differences were noted between the human and avian isolates.
- No intermediate mammalian host was identified in the transmission chain.
Implications:
- The findings suggest direct zoonotic transmission of H5N1 from infected chickens to humans.
- This case underscores the potential for avian influenza viruses to cross the species barrier.
- Intensified global influenza surveillance is crucial for early detection and prevention of avian-to-human transmission.