Romania's animal health and safety authority said a preliminary test on May 1 indicated that a cow slaughtered at an authorized abattoir was infected with bovine spongiform encephalopathy, or BSE.
It said the carcass has been sent to a British laboratory for further tests and it could be an "atypical form of BSE which appears naturally and spontaneously in cattle."
The officials only revealed the case after Russia decided to ban imports of Romanian beef, citing fears of BSE. It wasn't clear how the Russians learned about it.
They said Romania has not had a case of BSE since 1995 when testing began and there was no risk to public health from the current "isolated case."
BSE is fatal to cows and can cause a fatal brain disease in people who eat tainted beef. It first broke out in the late 1980s in Britain, where hundreds of people fell ill and many died after eating contaminated meat. Over the years, 4.5 million cattle were slaughtered to contain the spread.
Outbreaks followed in Japan in 2001 and Canada in May 2003.
Romania exports up to one million cattle a year, mainly to the Netherlands, Italy, and Croatia.