BioEd Online

A cat found dead last weekend on the German island of Rügen was infected with a dangerous strain of bird flu, health officials have confirmed.

Tests are being carried out to determine whether the virus is exactly the same as the aggressive H5N1 variant that has so far infected 174 people, mostly in Asia, more than half of whom have died.

German officials have ordered pet owners in areas where H5N1 has infected birds to keep their cats indoors and their dogs on a lead. But they also call for calm, noting that no cases have been reported in which a human has been infected by a cat.

Scientists are reluctant to be categorical however. The danger to humans is "theoretical, but nothing can be excluded", says Thomas Mettenleiter, head of the Friedrich Loeffler Federal Research Institute for Animal Health on the neighbouring island of Riems, off Germany's northern coast.

Cats and dogs

The dead cat is the first reported case of a mammal being infected with H5N1 in northern Europe. It has provoked panic in Germany where, as in most European countries, people have close relationships with their cats.

The largest reservoir for the virus is certainly in birds. But researchers have found signs of H5N1 in other animals. Thai cats and dogs, for example, have been found to have antibodies against the virus (see ' Thai dogs carry bird-flu virus, but will they spread it?').

And experiments carried out by virologist Albert Osterhaus have shown that cats fed H5N1-infected chicks become infected themselves within 24 hours; they can then infect other cats. The virus spreads throughout their bodies, including the gut, which means that a limited shedding of the virus in the faeces is possible, he says (see ' Bird flu's bodily harm revealed'). Very little is known about dog infections, adds Osterhaus, who is based at the Erasmus University in Rotterdam, the Netherlands.

Just one day before the dead cat was found on Rügen, Osterhaus gave the Dutch authorities a proposal for handling outbreaks of H5N1 in cats in the Netherlands, which is so far free of the disease.

"If the wild bird population becomes infected with H5N1 then cats should be kept inside," recommends Osterhaus. "And if outbreaks occur in poultry, farm cats should be quarantined."

Spreading fast

The H5N1 virus hit Germany in the middle of February. Since then 134 wild birds, mostly swans but also ducks and a few birds of prey, have been infected with bird flu in five German states. Of these, 122 cases occurred in Mecklenburg-Vorpommern, where Rügen island is located.

"There seem to be two independent outbreaks in the north and south," says Mettenleiter, whose lab is responsible for analysing the diseased birds. "And they are spreading fast."

So far German poultry have not been infected. Farmers have been forbidden to allow their poultry to remain outside.

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