Better understanding of bird flu in nature
WAGENINGEN/ROTTERDAM/AUSTRALIA – Bird flu among mallards in the Netherlands peaks twice a year, according to new research led by the Netherlands Institute for Ecology (NIOO-KNAW). The findings have been published online by the Journal of Animal Ecology. There is a minor bird flu peak during the summer, as the number of young ducks increases. And a major peak in autumn, coinciding with the arrival of migratory mallards. "That does not mean migratory birds are spreading the virus in the Netherlands."
"The pattern we witnessed in bird flu outbreaks among mallards", says NIOO-animal ecologist Jacintha van Dijk, "was that of two separate peaks." In summer, there tends to be a large number of juveniles. Their resistance is comparatively low (i.e. fewer antibodies in the blood), while the number of viral particles in their secretions is high. The same is true for migrants: they also have relatively low resistance and a high likelihood of being infected. "So it is probably fair to say that between them, juveniles and migrants are largely responsible for these natural bird flu peaks.'
A mild strain of the bird flu virus has long been common in waterfowl. "We did not see any sick birds as such", says Van Dijk. "There were no symptoms to set apart carriers of the virus." It is only when these mild strains spread to poultry farms, that a high pathogene version of the virus may develop. The research among mallards makes it possible to anticipate when there is the highest risk of this happening, allowing poultry farmers to consider seasonal measures.
"Our research has not yet shed any light on where these flu viruses actually come from", stresses Van Dijk. "They may well be resident in the Netherlands already." Although she says the researchers do know in which overall direction to look. "Millions of waterfowl spend the winter in the Netherlands. It is one of their main wintering areas."
The water bird most susceptible to infection with bird flu is Anas platyrhynchos: the mallard or wild duck. Animals were captured and sampled at a duck decoy during one year, at a much higher frequency than would normally be the case: once or twice per week. This made an accurate analysis of the timing of bird flu peaks during the year possible. It also made it possible to link these peaks to possible causes.
Much of the discussion about bird flu has been based on assumptions. The new research finally makes it possible to separate fact from speculation. A third factor often believed to be important beside the number of juveniles and migrants - the density of the bird population - was revealed by the research to play no clear role.
The research project was co-financed by the Netherlands Organisation for Scientific Research (NWO) and the National Institutes of Health (NIH) in the United States.
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The NIOO is one of the largest research institutes of the Royal Netherlands Academy of Arts and Sciences (KNAW), with more than 200 employees and students. It is specialised in fundamental and strategic ecological research. As of early 2011, the NIOO is based in a sustainably-built research laboratory in Wageningen, the Netherlands.
More information:
- Researcher Jacintha van Dijk M.Sc., NIOO-KNAW Department of Animal Ecology, T +31-31-7473420, j.vandijk@nioo.knaw.nl
- Researcher prof. dr. Ron Fouchier, Erasmus MC Department of Viroscience, T +31-10-7044067, r.fouchier@erasmusmc.nl
- Public information officer Froukje Rienks M.Sc., NIOO-KNAW, T +31-61-0487481 (mobile) / +31-31-7473590, f.rienks@nioo.knaw.nl
Article: Juveniles and migrants as drivers for seasonal epizootics of avian influenza virus, Jacintha G.B. van Dijk, Bethany J. Hoye, Josanne H. Verhagen, Bart A. Nolet, Ron A.M. Fouchier & Marcel Klaassen, Journal of Animal Ecology, Early View (Online Version of Record published before inclusion in an issue), 4 September 2013.
