Stronger research leads on AI transmission to humans
Research into avian influenza in a Cambodian village has provided
stronger evidence that it is difficult for humans to catch bird flu, and that
mild or asymptomatic human infections are uncommon.
The research by the European Centre for Disease
Prevention and Control was conducted in a village where
there had been extensive poultry deaths attributed to AI,
some lab-confirmed poultry infections, and one human death from H5N1.
Blood sampling of 351 people, carried out within a 1 km radius of the man's
house, showed that although the participants had frequent direct contact with
poultry, none of the participants had neutralising antibodies to H5N1. More than
70% of the households involved in the surveying reported poultry deaths in the
weeks before the man's death.
The findings from this Cambodian study strongly suggest that asymptomatic and
mild H5N1 virus infections did not occur in this human population and that H5N1
infection was difficult to acquire.
This presumption has been the basis of risk assessments carried out by the
European Centre for Disease Prevention and Control in the past year, although
the evidence base for this has been weak.
There had previously been no published population surveys with serological
support and the little published data that there was (mostly concerning contacts
of cases or occupational groups) had not specified where the laboratory testing
had been undertaken, or the methods used.
The study's findings will need to be replicated elsewhere before conclusions
can be drawn, but the public health advice issued by the ECDC is now better
supported scientifically. The results also emphasise that the risks to humans
from the many different avian influenzas, even highly pathogenic ones, must each
be considered individually.
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