Science - February 16, 2006

‘Bird flu is here to stay’

As it becomes clear that avian influenza is spread by wild birds, there is a need for more research on this relatively unknown phenomenon. According to ornithologist Tom van der Have and veterinary epidemiologist Professor Mart de Jong, Wageningen UR is the institution to perform the research.

‘Bird flu is not about to disappear,’ says Tom van der Have of the Resource Ecology Group. Last week Chinese researchers announced that three species of wild ducks in Southeast China that were infected with the highly pathogenic H5N1 virus in 2005. These were apparently healthy ducks, just before the spring migration. According to Van der Have, this is a strong indication that wild birds may be responsible for the spread of avian influenza. If this is the case, it will be difficult to fight the virus. ‘You can destroy poultry as a measure to fight bird flu, but it’s impossible to do that with wild migratory birds of course.’
It now looks as though the migratory birds will bring the H5N1 virus to the Netherlands. A number of people have already died in Turkey and Iraq, the virus has been found in dead geese and swans in Italy, Bulgaria, Greece, Slovenia and Austria, and there has been an outbreak in Nigeria near an important wintering area for water birds.
For veterinary epidemiologist Professor Mart de Jong, however, dead geese and swans are only circumstantial evidence. ‘As they say, dead birds don’t fly. What is more interesting is the birds that are infected with the virus, but are not sick.’ For in the Chinese research it is the healthy ducks that spread the virus.

Fighting symptoms
Up to now there was little scientific evidence to back up the claim that wild birds carry the avian influenza virus without dying from it themselves. De Jong and his colleagues have done experiments in which they have shown that the H7N7 virus – which caused the death of a vet during poultry clearance in 2003 in the Netherlands – can be present in otherwise healthy ringed teals.
Van der Have and De Jong are certain that bird flu will hit the Netherlands. The country has a huge concentration of large-scale poultry farms with hundreds of millions of chickens, turkeys, geese and ducks, so one incident could have serious consequences. The question is rather when it will happen and whether it will occur through the migratory birds.
In order to be able to answer this question in the future, researchers need to examine the relation between wild migratory birds and bird flu, according to Van der Have. At present research is focused on combating bird flu within the poultry sector. But we will remain at the level of fighting symptoms if we don’t learn more about the spread of the virus via the migratory routes. Van der Have would like to see the existing epidemiological models that De Jong uses, which now focus on infection within and between farms, scaled up to the level of bird migration.
According to Van der Have, little is known about the way in which the various avian influenza virus strains maintain themselves in different wild bird species. De Jong confirms this. ‘In models you’d like to know what percentage of the wild birds are infected, but at present we know little more than that some species are virus carriers.’ Like the ringed teal, that can spread the H7N7 virus while remaining healthy, and the wild ducks from China with the H5N1 strain. But, De Jong points out, this kind of research is complex and therefore expensive. ‘It’s not a question of just one wild bird species.’

Extra investment
Van der Have regards the Chinese research as a breakthrough. ‘This story helps us to zoom in. It has already been known for a long time that the wild duck Anas platyrhynchus is a reservoir for the avian influenza virus, but these ducks are not truly migratory.’ Researchers can now concentrate on the duck species from the Chinese research and work out the relations with worldwide migratory routes, for example using information in databanks.
Another important conclusion from the Chinese research that raises questions is the fact that, of the thirteen thousand birds, only eight were infected. ‘That is a very low incidence,’ declares Van der Have. ‘That explains why it is so difficult to trace the spread of viruses.’
Van der Have and De Jong are both of the opinion that Wageningen UR is the institution to do this kind of research, as both ornithological and epidemiological expertise are present. Currently, most research funds for avian influenza are earmarked for short-term work, and for prevention and control. In addition, researchers focus mainly on their own discipline.
‘Now we have a topical issue that fits WUR’s mission,’ says Van der Have. ‘Safe living environment and healthy food. Wageningen UR needs to come up with extra investment funds now to bring together researchers. It costs a lot of energy bringing diverse disciplines together, and researchers have little time to do it.’ The extra investment will lead to knowledge that can be used repeatedly in the long term, according to Van der Have. For avian influenza is here to stay.

Martin Woestenburg

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