The United States has reported its first suspected case of "mad cow disease", or BSE, in Washington state. BBC News Online answers key questions surrounding the issue.
Q: When will we know if the case has been confirmed?
A: In a few days' time. US officials carried out initial tests for BSE (bovine spongiform encephalopathy) on a sick cow on 9 December. A few days ago, those tests appeared to prove positive. A tissue sample was sent to a specialist laboratory in south-east England for confirmation.
The US has reported only one suspected case of 'mad cow' disease
The cow was described as a "downer animal", which meant it had problems walking. This is one sign of BSE.
Q: What anti-BSE measures has the US taken?
A: A quarantine has been imposed on the farm near Yakima, Washington, where the cow came from. Scientists are now investigating whether any meat from the animal could have entered the food chain. A senior administration official said the US Department of Agriculture was considering a recall order for meat in the distribution chain that could have been tainted.
The cow was sent to a slaughterhouse in Washington State, but parts of the animal also passed through three other facilities in the state. According to food safety officials, however, the cow's brain and spinal column, which are considered high risk for conveying BSE, were sent to a rendering plant. Cattle deemed unfit for human consumption are sent to such plants, where they are turned into pet food, oils and other products.
The US has introduced extensive anti-BSE measures since it appeared in Europe about 15 years ago.
Restrictions were placed on the imports of cows and sheep and products including meat, meat-and-bone meal, offal and glands from countries where BSE was known to exist or from countries thought to be at high risk of BSE.
In May, when a single case of mad cow disease was found in Alberta, Canada, the US was among a number of countries that banned the import of Canadian beef. The ban has been eased, and imports of boneless cuts and from cattle younger than 30 months have resumed.
There is also a feed ban, which makes it illegal to feed cattle remains of other livestock. Mad cow disease can be spread to other cattle if an infected animal is ground up for livestock feed.
In addition, there is also testing at slaughter. US Secretary of Agriculture Ann Veneman said on Tuesday that her department tested 20,526 cattle for mad cow disease last year. However, some 35 million cattle are commercially slaughtered each year.
Critics of government policy say that because no cases of BSE have been discovered in the US before now, officials have not put in place the kind of stringent testing that exists in some other countries, such as Europe and Japan.
Q: Do we know how the cow contracted BSE?
A: No-one knows yet but investigators are expected to focus on the animal's food supply.
Although the US has a feed ban, some banned material does make its way into cattle feed. In July, the Food and Drug Administration said that tests showed that 13 animal feed plants out of a total 1,555 had feed that
contained some of the banned material.
Canadian investigators were never able to pinpoint the cause of the disease discovered in a single cow in the spring.
Q: Is there any implication for human health?
Beef contaminated with mad cow disease consumed by humans can
cause a variant of Creutzfeldt-Jakob disease (vCJD), a brain-wasting disease. This has already claimed more than 140 lives in Europe, mostly in the UK.
US Agriculture Secretary Ann Veneman insists that there is little chance of people catching vCJD.
She says the cow's brain and spinal column, which are considered high risk for conveying BSE, had been sent to a rendering plant. However, some experts say that the fact that such cows are sent to rendering plants does not guarantee that infected material will not enter the food supply.
Other experts say that even if beef from one infected cow got into the food supply, the chances that any consumer would develop vCJD are extremely low.
Q: How has world reacted?
A: The two biggest buyers of US beef, Japan and Mexico have halted imports, along with many European and Asian countries.
Canada, the third biggest foreign market for US beef, said it would wait for confirmation on the test results before taking any action.
The European Union already has restrictions on imports of US beef because of a dispute over the use of beef hormones. It says it has no immediate plans to impose further restrictions.
Q: What impact could this have on US cattle industry?
If the main countries that import beef continue with their bans and US consumers lose faith in one of their favourite foods, the results could be devastating.
The US beef industry is worth some $40bn dollars a year. America produces a quarter of the world's beef supply and beef forms a part of nearly 78 million meals eaten across the United States every day.
A single case of mad cow disease in Canada cost the industry billions of dollars. While official figures are hard to come by, a private study released last month estimated that Canada's beef industry lost $2.5bn in the six months since May.
Some countries, such as Japan, still ban imports of beef from Canada.