Health officials urged cat owners to keep pets indoors after the dead cat was discovered over the weekend on the Baltic Sea island of Ruegen, where most of the more than 100 wild birds infected by the H5N1 strain have been found.
The cat is believed to have eaten an infected bird, said Thomas Mettenleiter, head of Germany's Friedrich Loeffler Institute. That is in keeping with a pattern of disease transmission seen in wild cats in Asia.
Mettenleiter insisted, however, there was no danger to humans as there have been no documented cases of a cat transmitting the virus to people.
However, Maria Cheng of the World Health Organization in Geneva said there was not enough information on how the disease is transmitted to be sure. She noted that tigers and snow leopards in a zoo in Thailand became infected after being fed chicken carcasses, dying from H5N1 in 2003 and 2004.
"But we don't know what this means for humans. We don't know if they would play a role in transmitting the disease. We don't know how much virus the cats would excrete, how much people would need to be exposed to before they would fall ill," Cheng said.
In addition to the large cats infected in Thailand, three house cats near Bangkok were infected with the virus in February 2004. Officials said one cat ate a dead chicken on a farm where there was a bird flu outbreak, and the virus apparently spread to the others.
WHO said tests on three civets that died in captivity last June in Vietnam also detected H5N1. The source of that infection was unknown.
Twenty-one people in Turkey tested positive for H5N1 in January and four of them, all children, died.
WHO on Monday raised its official tally of human bird flu cases worldwide to 173, including 93 deaths. Almost all human deaths from bird flu have been linked to contact with infected birds.
Health officials are concerned H5N1 could mutate into a form that is transmitted easily among humans, which could lead to a pandemic.
Cheng said the discovery of bird flu in a cat in Germany underscores that the deadly H5N1 strain can infect a wide range of mammals.
Scientists are particularly concerned about bird flu infecting pigs, because swine can also become infected with the human flu virus. The fear is the two viruses could swap genetic material and create a new virus that could set off a human flu pandemic.
"We're particularly worried about pigs because they can have both human and bird flu at the same time and they can pass it on back to humans in a new form, which is essentially what happened in the last two pandemics" in 1957 and 1968, Cheng said.
Several other European nations registered cases of H5N1 on Tuesday. The worst outbreak was in Russia, where authorities confirmed the illness that devastated a poultry farm in the southern region of Krasnodar was bird flu.
More than 100,000 chickens at a farm in the village of Lavliniskaya have been killed to try to stem the spread of the disease, Gov. Alexander Tkachev said.
Forty-three countries — including the United States — have partially or totally banned French poultry products after H5N1 was confirmed in commercial birds over the weekend. A group of veterinary chiefs meeting in Paris said Tuesday no country should consider itself safe from the deadly strain and that it is "highly likely" the disease will continue its spread in poultry stocks in Europe and beyond.
"The risk now is high for everybody," said Bernard Vallat, director of the Paris-based World Organization for Animal Health, which hosted the two-day meeting of experts from 50 countries.
Authorities in Sweden and Hungary also said they were conducting further tests to confirm whether wild birds that had tested positive for a form of bird flu were infected with the H5N1 strain.
Slovenia, as well as the southern German state of Bavaria, both registered new cases of H5N1 in wild fowl.
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