VIENNA/ZURICH (Reuters) - Austria and Switzerland on Thursday took precautionary steps to prevent the spread of bird flu to domestic poultry after discovering cases of the disease in wild ducks around Lake Constance, the latest in a series of cases across Europe.

Austria ordered farms within 1 km (0.6 mile) of the shoreline of the lake, which also borders Germany, to keep all poultry indoors. Switzerland took similar measures.

Austrian and Swiss authorities have discovered a highly pathogenic strand of the H5N8 bird flu in the corpses of several wild ducks in the area this week, although they said there was no evidence the virus could be transmitted to humans.

The creation of a "protection zone" to keep migrating birds from transmitting the disease to farm poultry will be implemented on Thursday in coordination with Switzerland and Germany, a spokesman for Austria's health ministry said.

In Austria, the measure also requires poultry farmers and owners of pet birds to have a veterinarian check their animals at least once a month.

In Switzerland, farms with more than 100 birds have to keep track of animals presenting particular symptoms, the Federal Food Safety and Veterinary Office said in a statement.

Although no infected birds have been found near other Swiss lakes and rivers so far, the office protectively set up surveillance zones around lakes and canals including Lake Geneva and Lake Zurich.

Austria is also investigating a case of suspected bird flu in a domesticated bird in Vorarlberg province and expect final results on Friday.

If the tests are positive, authorities would have to cull all birds in the affected farm and establish a 3-km protection zone and 10-km surveillance zone around the site, the spokesman said.

The Dutch government said on Wednesday it had ordered farmers in the Netherlands to keep poultry flocks indoors after wildfowl infected with bird flu were discovered in several European countries.

Germany has reported an outbreak of H5N8 in the northern state of Schleswig-Holstein, the World Organisation for Animal Health said on Thursday.

Hungary's food safety authority said last week it had found traces of bird flu at a poultry farm in eastern Hungary and would destroy 9,000 turkeys to protect nearby populations.

(Reporting by Shadia Nasralla in Vienna and Silke Koltrowitz in Zurich; Editing by Hugh Lawson)