BERLIN (Reuters) - A third case of a chicken testingpositive for the deadly H5N1 bird flu virus in the northeastGerman state of Brandenburg was confirmed by state authoritieson Wednesday.

A police spokesman in Neuruppin, north of Berlin, confirmedthat a chicken on a small farm in the town of Blumenthal in theOstprignitz-Ruppin district had tested positive for the virus.

All 31 birds in the village were culled. It was the thirdcase in 10 days in Brandenburg, a rural state that surroundsBerlin and is on the border with Poland. There have been eightcases of the H5N1 bird flu virus in Poland this month.

Officials in Brandenburg sealed off a protection zone witha radius of three km (two miles) and imposed a surveillancezone of 10 km radius around the area. There are 150,000 birdsin the 10-km zone.

Earlier this month, two chickens in the Oberhavel districtfurther west tested positive for H5N1. Eleven birds in a smallOberhavel farm were suspected of having the virus, of whichfive died and two were sent for tests which proved positive,the state Agriculture Ministry said.

A week ago, a separate case of bird flu was confirmed inthe town of Bensdorf in the Potsdam-Mittelmark district,bringing the number of bird flu cases in the state to 24.

German authorities culled tens of thousands of birds afterthe virus was found at two farms in Bavaria early this year.

Although experts fear the H5N1 strain could spark a globalpandemic and kill millions of people if it mutates, it hasinfected relatively few humans in its present form.

Since 2003, nearly 350 people worldwide are known to havecontracted the H5N1 virus, of whom more than 200 have died.

(Reporting by Erik Kirschbaum, editing by Tim Pearce)