New avian influenza virus A H5N7 identified in ducks in Denmark
EU - A new influenza A virus type, H5N7, has been identified for the first time in ducks in Denmark (1).
25 September 2003
4 minute read
Following disease among 12 000 ducks raised to be released for hunting at a duck farm near the town of Salling in Jutland, two viruses were identified: a Duck Virus Enteritis (DVE), which caused the disease, and an influenza A virus. All ducks had to be exterminated on 10 September 2003, due to the disease.
The influenza A virus was isolated from the tissues of several of the ducks. The Statens Serum Institut used full length haemagglutinin and neuraminidase reverse transcript-polymerase chain reaction (HA and NA RT-PCR) with routine sequencing, which is used directly on clinical samples rather than cultured virus, to genotype this new virus as H5N7. This type has never previously been identified and further analysis is now being carried out on the virus. Importantly, this new virus has not been detected in humans, especially not among those people who had contact with these ducks, or in several unrelated influenza A virus cases (H3N2) diagnosed in Denmark since 1 September 2003. Twelve avian influenza A virus (AIV) strains have been isolated from wild birds in Denmark since 1996, none of which have been H5 or H7.
Influenza A viruses are divided in 15 subtypes based on HA (H1-15) and 9 subtypes based on NA (N1-9). Wild birds seem to be the natural reservoir for avian influenza (AIV). Although low pathogenic H5 and H7 exist, all highly pathogenic AIV are either H5 or H7. Pathogenicity of H5 and H7 AIV depends at least partly on the amino acid sequence at the cleavage site in HA1/HA2. Such pathogenic sequences were not found. Therefore this AIV strain is being grouped as having low pathogenicity.
The potential to change pathogenicity, during replication in birds or recombination in pigs and/or humans, for example, is not known. Highly pathogenic AIV of type H5 and N7 have occasionally infected humans. This occurred in Hong Kong in 1997 (H5N1) where 6 of 18 infected patients died (2), and again in 2003 where 1 of 2 infected humans died, and in the Netherlands (H7N7) (3) in 2003 where 1 of 80 infected patients died. The World Health Organization has recommended that all countries establish national pandemic planning committees in case of influenza epidemics (http://www.who.int/csr/disease/influenza/pandemic/en/). Laboratory surveillance networks and fast genotyping methods should be integral to the work of these national committees.
References:
Statens Serum Insitut [Denmark]. New influenza virus identified for the first time in the world at Statens Serum Institut. News item, 19 September 2003. (http://www.ssi.dk/sw419.asp?PAGE=1&ArtNo=2019067) [accessed 24 September 2003]
Claas EC, Osterhaus AD, van Beek R, De Jong JC, Rimmelzwaan GF, Senne DA, et al. Human influenza A H5N1 virus related to a highly pathogenic avian influenza virus. Lancet 1998; 351: 472-7.
(http://www.thelancet.com/journal/vol351/iss9101/full/llan.351.9101.original_research.7618.1)
Crofts J. Avian influenza human death reported in the Netherlands. Eurosurveillance Weekly 2003; 7(17): 24 April 2003. (http://www.eurosurveillance.org/ew/2003/030424.asp)
Anders Fomsgaard ( ) and Karoline Bragstad, Department of Virology, Statens Serum Institut; and Poul Jørgensen, Danmarks Veterinærinstitut (Danish Veterinary Institute), Aarhus, Denmark
