"We are getting calls from cat owners wanting to know if there are risks, people who are panicking and wondering what they should do with their cats, and people who are abandoning their cats," said the association's president, Serge Belais, in a telephone interview with The Associated Press.
"A panic is starting," he said. He said he had no immediate figures on how many cats are being abandoned, but added: "The risk is that we'll see the deluge in the days or weeks to come."
The German cat was the first infected mammal in continental Europe. It was found over the weekend on the island of Ruegen, where more than 100 wild birds have tested positive for H5N1. The cat is believed to have eaten part of an infected bird, following a pattern of disease transmission seen in big cats in Asia.
On Wednesday, German officials agreed to order cats kept indoors and dogs on a leash in a 2-mile radius around areas with confirmed H5N1.
The German cat case "shows the high degree of alertness and the very effective surveillance system in place in Europe" against H5N1, said the Paris-based World Organization for Animal Health, which has more than 160 member countries.
It backed recommendations that owners of cats that run free in areas where H5N1 has been detected take their pets to a veterinary surgeon if they show signs of having a severe cold.
Even before the German case was announced Tuesday, France's government had asked the national food safety agency for a study on the risks of cats getting bird flu. Results are expected this week.
The French prime minister, Dominique de Villepin, asked cat owners Wednesday not to let their pets stray into bird flu-infected areas. So far, H5N1 in France has been found only in the southeastern Ain region, in wild ducks, swans and on a turkey farm.
The animal protection society said it was writing to the government to ask it to ensure that French mayors do not respond to bird flu fears by launching stray-cat eradication programs.
Belais advised people to keep their cats indoors, both for fear that they might fall victim to municipal cat-catchers and to minimize any risk from bird flu. He said the risks of cats contracting H5N1 bird flu are "less than minimal."
By John Leicester