US officials identified a possible third case of BSE in an animal tested as part of the enhanced BSE surveillance program on Friday (10 March) evening.

A sample from the suspect animal returned an inconclusive test result in the less accurate rapid-screening tests. The US Department of Agriculture is currently conducting further tests at the National Veterinary Services Laboratories using an immunohistochemistry test. Additionally, officials said, the USDA's Agricultural Research Service will conduct a Western blot test. The results of these will be released within the next week.

Until then, the USDA has emphasised that the inconclusive result does not necessarily mean that the animal was infected with the disease. "This inconclusive result does not mean we have found a new case of BSE. Inconclusive results are a normal component of most screening tests, which are designed to be extremely sensitive so they will detect any sample that could possibly be positive," said John Clifford, chief veterinary medical officer at APHIS.

"In addition, this animal did not enter the human food chain nor the animal feed chain," he said. "I want to emphasise that human and animal health in the United States are protected by a system of interlocking safeguards and that we remain very confident in the safety of US beef."

Nevertheless, the inconclusive result comes at a difficult time for the US, with negotiations to re-open the Japanese and South Korean boarders to US beef moving slowly.