By Nilesh, WHO Correspondent, [RxPG] - Highly pathogenic H5N1 virus replicates in the respiratory and intestinal tracts of experimentally infected domestic ducks and contact ducks. Large amounts of virus (103.5 10 5.5 per ml) are excreted via the respiratory route as well as in faeces.
- No symptoms or deaths were observed in the majority of ducks and contacts infected with human and chicken H5N1 viruses from the 2004 outbreaks in Viet Nam.
- The amounts of H5N1 virus shed are sufficient to allow transmission of H5N1 infection directly from apparently healthy ducks to chickens.
- All infected ducks shed virus for 11 days and some for 17 days and longer. In comparison, ducks infected with an H5N1 virus isolated in 2003 shed virus for a maximum of 10 days.
- Preliminary results on the environmental stability indicate that H5N1 viruses from the 2004 outbreaks have become more stable. H5N1 viruses from 2004 survived at 37oC for 6 days, compared with 2 days for viruses from the 1997 outbreak.
The studies were completed last week by researchers at the WHO collaborating centre for animal influenza viruses at St Jude Childrens Research Hospital in Memphis, USA. The main findings are being made public, in advance of publication, because of their significance for human health.
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