Although the United States is the world’s largest producer of beef, it is still importing more beef than it is exporting, thanks in part to Bovine Spongiform Encephalopathy, commonly known as Mad Cow Disease.

The degenerative disease affects the central nervous system of adult cattle, and the human variant of the disease, Creutzfeldt-Jacob Disease, can occur if tissues containing infectious prions, virus-like protein particles, are consumed by humans.

Bans and restrictions on U.S. cattle imports to other countries are still in place after BSE was confirmed in Washington in December 2003, and the U.S. cattle market this year has exported only 15 percent of what it exported last year, according to the Economic Research Service for the U.S. Department of Agriculture. The trend is expected to remain the same until trade policies are changed.

“We are currently trading with Canada, Mexico and some Caribbean countries,” said John Lawrence, professor of economics in agriculture. “We are working to re-open the borders with other countries.”

Japan agreed to re-open trade with the United States in October, and procedural development has begun in both countries, although the case of Mad Cow Disease found in a 23-month-old bull in Japan is slowing negotiations, especially because it was generally thought that animals younger than 30 months could not develop the disease.

This finding could affect U.S. import policy for Canadian beef. The United States only imports boneless beef less than 30 months of age from Canada, which is at low risk to contain the disease, but soon it might be importing live cattle as well.

“There is a rule process that we are going through now to accept live animals from Canada less than 30 months of age,” Lawrence said.

If this occurs and there is a possibility that BSE will be present in some animals, testing may have to be done on all cattle, not just those older than 30 months.

Around 130,000 screening tests for the disease have been conducted in the United States since June 1, said Nolan Hartwig, professor in veterinary diagnostic and production in animal medicine; all three of the inconclusive cases tested negative at the USDA National Veterinary Services Laboratories in Ames.

“When it’s an inconclusive test, then they’re sent to NVSL here,” Hartwig said. “It’s the federal reference laboratory for the United States.”

The national laboratories conduct a highly accurate immunohistochemistry test on beef samples and sometimes also use a western blot technique.

“I think that people trust the official USDA test,” Lawrence said. “They also approve of the screening test. What concerns some people is the announcement of an inconclusive test before it has been confirmed.”

After a possible case of Mad Cow Disease was announced in the United States in November, the cattle market dropped slightly.

“The beef industry was watching closely, but there didn’t seem to be a lot of consumer reaction based on the preliminary test results,” Lawrence said. “The market dropped one day, but had recovered and moved higher than before following the official announcement that it was negative.”

The sensitivity of the screening tests sometimes leads to false positives for the disease, Hartwig said, but that is better than getting false negatives.

But inconclusive tests that are prematurely announced to the public tend to cause a negative market reaction that can be bad for the economy, Lawrence said.

Many measures are taken to ensure food safety in the United States. Despite the fact that another positive test for BSE may be found in the future, the protective policies in place will help to protect consumers.

“I will not be shocked if we get a positive,” Hartwig said. “But the control procedures that we have in place make me confident that it’s so extremely rare it’s not a public health risk.”