WASHINGTON (Reuters) - Turkeys at a farm in Virginia hadantibodies to a low-risk strain of bird flu but direct evidenceof infection has not been found, the U.S. Department ofAgriculture said on Wednesday.

None of the birds became ill but 54,000 were beingslaughtered as a precaution, said Dr. John Clifford of USDA'sNational Veterinary Services Laboratories.

The turkeys had antibodies to a low pathogenic form of theH5N1 avian influenza virus, Clifford said. This strain of H5N1does not usually make birds ill, although it could potentiallychange into a more dangerous form if allowed to spread.

"Every indication is that the virus detected is consistentwith the North American strain of low pathogenic H5N1, which isnot a human health concern," Clifford said in a statement.

"The turkeys showed no signs of illness, and there was nomortality. Thus far, there is no evidence the virus is actuallypresent in the samples collected. The testing detected onlyantibodies, which indicate possible past exposure to thevirus."

Officials around the world are monitoring birds for allforms of avian influenza. The highly pathogenic H5N1 strain isthe cause of greatest worry because of its occasional deadlyspread to people.

It has been found in 59 countries in Asia, Europe andAfrica but has yet to be detected in the Americas. It is deadlyto chickens and sometimes infects people.

H5N1 has killed 192 of the 318 people known to have beeninfected, according to the World Health Organization.

According to the world animal health organization OIE,outbreaks of highly pathogenic avian influenza have beenreported in birds in France, Germany, Bangladesh, and Vietnamthis month. Malaysia, the Czech Republic and Togo have alsobeen fighting outbreaks.