Even if the weather speaks against it: Spring is approaching inexorably - and with it the migratory birds. However, concerns are already growing as to whether the animals are bringing an insidious cargo with them and are spreading H5N1 across the country. Dead swans and a dead hawk on Rügen feed these fears.
Now the time has come: Bird flu has reached Germany. After years of rampaging the H5N1 virus, which is also potentially deadly for humans, in East and South Asian poultry stocks, the pathogen made its way west last summer. It first reached Mongolia, Russia and Kazakhstan - which took months - and then Ukraine, Croatia, Romania and eastern Turkey. Emergency measures were passed everywhere and huge flocks of chickens, ducks and geese were culled in barns and on farms.
In Turkey, however, the fight against the epidemic came too late for four people; they died in regional hospitals. Since then, things have happened in quick succession: the virus crossed the border into Iraq and claimed another life there. At the same time, it reached suburbs of Istanbul. Then H5N1 jumped to Greece and from there to Italy, Slovenia and Austria, and now it also appeared in Germany for the first time: the Robert Koch and the Friedrich Loeffler Institute issued official confirmation that in two by tourists mute swans (Cygnus olor) found dead on Rügen on February 8th and a goshawk (Accipiter gentilis) that was found to be infected with bird flu from Asia.
Consequently, crisis management teams are being set up all over the country, and there is renewed concern among politicians, farmers and much of the rest of the population about a major epidemic of the disease. Not only could it cause major economic damage, it could also cost lives in the worst case. But what about the suspiciously eyed risk of migratory birds?
Lethal to wild birds
First of all, one thing can be said: So far, there is still not a single proven case of a migratory bird that carried the H5N1 virus or a direct mutation of it, but did not contract it. At least that's what random studies of shot waterfowl suggest. In the case of the Croatian outbreak in October 2005, in addition to the two dead H5N1-positive swans, another 2000 wild and farmed poultry samples tested negative. Avian flu is therefore still deadly for wild birds and weakens them to such an extent that they cannot migrate over long distances - further introduction of the germ by long-distance migrants, for example from Nigeria, can therefore be ruled out given the current state of affairs.
Franz Bairlein, head of the Institute for Bird Research in Wilhelmshaven, does not consider the possibility of a dormant H5N1 virus in the bodies of swans and other waterfowl to be ruled out. Because the mute swans affected in Germany do not belong to the classic migratory birds. Under normal conditions, they stay where they are and at best cover short distances - for example from the Gulf of Bothnia in the eastern B altic Sea or the B altic States to Rügen or from the Black Sea region and Turkey to southern Italy. The trigger for a possible departure could be the freezing of inland waterways and bays in Eastern Europe. However, as things stand, north-eastern Europe is not considered to be affected by bird flu.
So it's possible that they only got infected in this country - for example from other waterfowl that had previously been infected by conspecifics or pets but survived this virus uptake. Only the hard winter in Europe and lack of food weakened the swans to such an extent that they fell victim to the disease. The catch: After all the studies on thousands of wild birds in Europe, there is still no evidence of such a silent reservoir or a corresponding mutation of the virus. For this reason, wild birds should now be examined more intensively for the H5N1 virus in order to determine whether and to what extent the pathogen is widespread in the animals, says Bairlein.
Since wild birds have always died of H5N1 within a few days, experts from the international bird protection organization Birdlife International - which also supports research work - assume that at least the swans that died in Slovenia, Italy and Greece shortly before their departure infected. The scientists are considering meadows fertilized with chicken droppings as a possible source of infection – a common practice in Eastern Europe. It cannot therefore be ruled out that virus-contaminated manure was also spread, which the wild birds then ingested while grazing. That is why the Food and Agriculture Organization (FAO) warns against improper handling of poultry manure, as viruses can remain in it for weeks.
The common use of poultry manure as fish feed in parts of Russia, Ukraine, Moldova and other Eastern European countries is also problematic. Several of the outbreaks in Europe recorded by Birdlife International and the Radolfzell Ornithological Institute (Max Planck Institute for Ornithology) to date have taken place at fish farms - for example in Croatia or Romania, so that this possibility of transmission cannot be ruled out either.
Of the native waterfowl, swans appear to be the most vulnerable to avian influenza, having been among the top victims of most European outbreaks to date. They probably excrete small amounts of the germ before and after they die, without other wild birds being infected in the cases that are now known. This also does not necessarily indicate a greatly increased risk from wild ducks or geese, which are nevertheless a known natural reservoir for a large number of different influenza viruses.
Illegal Poultry Transport
There are other indications that migratory birds are not common busy H5N1 slingshots. Most of the epidemic outbreaks in Russia, Kazakhstan and Mongolia, for example, started in poultry farms located along important highways and railway lines - it is therefore quite likely that they were brought in by illegal poultry transport. After the occurrence of individual bird flu cases in South Korea and Japan - triggered by the import of infected duck meat - and the subsequent eradication in 2004, both countries have again been spared to this day. And this despite the fact that new crises are constantly becoming known in neighboring China and the two countries are the destination of a large number of migratory birds. Australia and New Zealand are also free of bird flu, where millions of migratory birds from East Asia and Siberia also arrive in the southern summer.
And the emergence of H5N1 in an African country is also more likely to be linked to illegal imports of poultry, according to Nigerian Agriculture Minister Adamu Bello. His authority therefore suspects imports from China or Turkey. Significantly, the disease broke out in Nigeria in a closed cell battery, which is not possible via migratory birds: it must therefore have been brought there involuntarily by humans. In addition, there are currently no bird migration movements from Europe or the Middle East to West Africa, so this route can actually be ruled out.
Even if it is still not clear which part the migratory birds play in the transmission of bird flu, the measures currently introduced in Germany are met with the approval of nature conservationists. Above all, the import bans on poultry from affected countries and the ban on the wild bird trade are welcomed. At the same time, the nature conservation organizations warn against panic reactions when dead birds appear, because at the end of a harsh winter, the natural mortality rate of weakened animals increases without this being attributable to bird flu.
Franz Bairlein also considers the risk of the disease spreading from wild birds to humans to be very low: the animals are too shy for close contact. Only dead or obviously sick birds should not be handled carelessly.