Washington ? The Agriculture Department is investigating a possible case of mad cow disease, the agency’s chief veterinarian said Saturday.

A routine test indicated the possible presence of mad cow disease, said John Clifford, the USDA official. The agency would not say where the animal was from.

The cow did not enter the human or animal food chain, Clifford said.

The department is conducting more detailed tests at its laboratory in Ames, Iowa, and should have results in four to seven days.

“This inconclusive result does not mean we have found a new case of BSE,” Clifford said, giving the abbreviation for the disease’s formal name, bovine spongiform encephalopathy.

“Inconclusive results are a normal component of most screening tests, which are designed to be extremely sensitive,” he added in a statement.

In humans, eating meat products contaminated with mad cow disease has been linked to more than 150 deaths worldwide from variant Creutzfeldt-Jakob Disease, a rare and fatal nerve disease.

A majority of the deaths were in Britain, where there was an outbreak of mad cow disease that started in the mid-1980s. There was one case confirmed in the U.S., although the federal Centers for Disease Control and Prevention believes the person got the disease while in the United Kingdom.

No one is known to have contracted the disease inside the United States.

U.S. government investigators have found two cases of mad cow disease. The first was in December 2003 in a Canadian-born cow in Washington state. The second was in June in a cow that was born and raised in Texas.

The United States has had three cases in which “inconclusive” results turned out to be negative. Two of those times were in 2004 and the third was in 2005.