NIEUWERSLUIS / ROTTERDAM / WIERINGERWERF -- Migratory swans carrying a mild form of avian influenza depart from The Netherlands more than a month after their healthy counterparts do. They also feed slower and fly shorter distances. These insights will be published on January 31, 2007 in PLoS ONE, the International, peer-reviewed, open-access, online publication from the Public Library of Science (PLoS) by scientists from the Netherlands Institute of Ecology (NIOO-KNAW) and the Department of Virology of the Erasmus MC. This contrasts previous ideas that mild forms of bird flu do not cause illness among wild birds. Moreover, these patterns can affect the rate of spread of avian influenza.
Wild birds were thought not to suffer from mild forms of avian influenza. But new data suggest that so-called low-pathogenic avian influenza viruses do affect the lives of birds. The Bewicks swan (Cygnus columbianus bewickii) is a migratory bird that breeds in NW-Russia and overwinters in NW-Europe, especially in The Netherlands. In this species, a team of ecologists and virologists showed that infected individuals initiate their migration by the end of January or early February, while uninfected individuals already do so by the end of December. Also, their next fuelling station is only 35 km away instead of the usual 250 km. Sick birds fuel at a lower rate: they take fewer bites per day and their digestion seems to be impaired. Presumably, this is due to their need to channel more energy towards their immune system.
Being ill is no fun for us, but for a migratory bird being ill could potentially mess up its whole calendar for the rest of the year. According to scientist Jan van Gils from NIOO, "Infected swans clearly suffer from their mild disease. The late departure from the wintering grounds could lead to late arrival in the breeding grounds, and thus to a lost breeding season. All in all, these low-pathogenic viruses have a much greater impact than pr
Contact: Froukje Rienks
Public Library of Science