Spread of bird flu: Experts are puzzled
By Elisabeth Rosenthal International Herald Tribune
WEDNESDAY, MARCH 1, 2006
OZZANO EMILIA, Italy As new outbreaks of bird flu have peppered Europe and Africa in the last few weeks, experts are realizing that they do not fully understand how migrating birds disseminate the H5N1 virus, leaving the continents vulnerable to unexpected outbreaks.
Just after new scientific research clarified the role of wild birds in spreading H5N1 out of its original territory in southern China, the virus promptly moved into dozens of locations in Europe and Africa, following no apparent pattern and underlining how little scientists actually know.
In fact, current knowledge of how H5N1 is spreading in Europe and Africa is so rudimentary that experts say there is absolutely no way of predicting where it will strike next - although they are now certain that it will, again and again. [comment: how can they be so sure??]
"We know next to nothing about this virus; we have only anecdotal information about where it exists and what birds it infects," said Vittorio Guberti, head veterinarian at the Italian National Institute for Wildlife, who has devoted his career to studying influenza in wild birds. "We don't even know where to focus. We have to sit and wait for the big epidemic to occur, and in the meantime there will probably be small outbreaks all the time."
Scientists do not know, for example, which species are the major carriers of H5N1. While they suspect that there may be a few areas at the fringes of Europe that are perpetually infected with H5N1, they are not sure exactly where. And while they are convinced that the virus can be carried on trucks, shoes and in fertilizer, they are not sure how important that route is.
Until this year, Europe's small fraternity of wild bird researchers, like Guberti, was severely underfinanced, its warnings about bird flu unheeded. Now they are racing to fill in gaps in knowledge and answer crucial questions.
"Think about this," Guberti said in his cluttered laboratory here. In March, "two million ducks from Nigeria, where there is a big problem, will arrive in Italy. And we don't know a thing about them."
Outbreaks in Nigeria have occurred in commercial poultry, but there is no information about whether the disease is in wild birds. Samples from African birds have been shipped to the official United Nations laboratory in Padua, Italy, for analysis, but they are "waiting on a shelf" because the lab is overwhelmed by samples from Europe now, a United Nations official said.
"There is a lot of money coming in from the World Bank, but most of it's going to pharmaceutical companies, although that is starting to change," said Alex Kaat, spokesman for Wetlands International, a Dutch nonprofit organization that has sent teams to several African nations to sample wild birds. "Everyone ignored wild birds for a long time - too long. And now we have a lot to learn."
In the past month, reports of the diseased birds have flowed in from more than a dozen widely separated countries, including Germany, Iraq, Egypt, Italy, France, Sweden and, most recently, Niger.
Since three weeks ago, when mute swans in Sicily became the first birds in the European Union to die from bird flu, Guberti said his life had been "a nightmare." He spent last weekend trying to trap swans in Sicily to see if the 200 or so remaining were infected.
On a bleak, rainy afternoon last Friday, Guberti's colleague Mara Scremin was taking blood samples from mallards on Italy's Adriatic coast, dressed in full biosafety gear because of the discovery of bird flu in an Italian duck last week.
In Slovenia, scientists have been trying to make sense of the 11 dead mute swans that have been found near lakes and rivers near the eastern city of Maribor, said Tomi Trilar, a senior biologist at the Slovenian Museum of Natural History. Like many countries, Slovenia has a native year-round population of about 100 swans, as well as visiting birds.
"They are really more vagrants than migratory birds, who fly short distances in search of food if there is a shortage in their normal wintering place," Trilar said, noting that Slovenian lakes are good resting places for hungry swans, since residents tend to feed them. "This year was very cold in southern Russia and the lakes were iced over, so we think the sick birds came from there."
But he said that "it is very hard to check" if there is also bird flu in the native population.
"They are huge birds and shy, and they struggle," Trilar said. "You can go to a site and sample one bird a day."
In February, new research provided crucial clues about how the H5N1 virus broke out of its original stalking grounds in Southeast Asia, moving to western China and on to the edges of Europe late last year. Bird flu was first discovered in Hong Kong in 1997.
The critical viral transfer took place in Guangdong Province, new genetic analysis suggests, when wild ducks or geese acquired the virus from domestic poultry in rice paddies where they coexisted.
Scientists at the University of Hong Kong have been studying subtypes of H5N1 virus in the birds of Guangdong for a number of years. Last month, they reported that the genetic types found in both wild and domestic birds in the province matched exactly the types found last summer in migrating bids in western China, proving a positive link.
Guan Yi and his colleagues reported in the Proceedings of the National Academy of Sciences last month that some birds infected with H5N1 could survive for a week, and so were capable of spreading it over vast areas - to China's remote west and Mongolia, for example. Previously, scientists were convinced that infected birds would be too sick to cover such distances.
From there, H5N1 predictably moved on to Russia, Ukraine, Turkey, Romania and the Balkans. But the recent pattern of spread, into European and African nations, has been far more confusing.
"For a couple of weeks, it was raining dead swans all over Europe, which left everyone scratching their heads," said Jan Slingenberg, a senior veterinary official at the United Nations Food and Agriculture Organization in Rome. "Are the swans just the tip of the iceberg? Where should we worry? But given the rapid geographic spread in so many different places, it is a good idea for everyone to be stepping up security."
Wetlands International has made a list of 17 species that it believes are particularly likely to spread H5N1 in Europe. There is no list for Africa or Asia. Some species, like pigeons, which have provoked intense angst in European cities, are not susceptible, so there is little point in directing vigilance there.
Guberti and others suspect that there are now permanent reservoirs of the disease on Europe's doorstep, so that birds like the mute swan may pick up the disease as they enter the Continent. Suspects include the Black Sea and the lower Volga River, areas that have
known outbreaks of H5N1 and where mute swans often winter.
Nations must identify such reservoirs, Guberti said, so that scientists can see which birds live there and where they migrate, creating a kind of early warning system. The dead ducks that have been found in various corners of Europe, from Geneva to central Italy and the suburbs of Lyon, have proved even more disquieting to scientists.
"It's hard to explain," said Kaat, the spokesman for Wetlands International.
He noted that scientists had no idea whether the ducks got the virus from infected poultry nearby, from mute swans, from another species that is spreading the disease undetected in Europe - or if they are birds making an early migration from infected parts of Africa.
While ornithologists are convinced that most of Europe's cases are tied to migration, they are also quick to note that wild birds are sometimes unfairly blamed. Officials in Turkey and Nigeria said that migrating birds were responsible for H5N1 outbreaks, though scientists said the distribution made that unlikely.
"It's easy to blame migrating birds, because then no one is responsible," said Juan Lubroth, a senior veterinary health officer at the UN and food and agriculture agency in Rome.
In Croatia, for example, Kaat said, fertilizer made of manure from infected poultry probably spread H5N1. Manure from farms is commonly used to fertilize fish ponds, which are frequent stopover points for migrating birds that probably contracted the virus there, he said. The virus persists in water for weeks.
In Nigeria, the first huge outbreak occurred in January in hens in the country's north, a dry area far from the wetlands that are home to the country's migratory birds.
"The outbreaks were in the wrong place and at the wrong time of year," Kaat said.
Instead, he and others believe, Nigeria's problem was probably caused by the transport of sick birds or bird products infected with H5N1 from another country in Africa or even Asia.
Most experts doubt that wild migrating birds themselves will precipitate huge outbreaks, since they are less susceptible than poultry to the virus, though they believe that Europeans must get used to a steady stream of wild bird deaths here and there.
Although H5N1 does not readily infect humans or spread among them, scientists worry that it could acquire than ability, setting off an deadly human influenza pandemic.