Herds Quarantined in Us Mad Cow Case

American officials were yesterday trying to determine whether the country's first case of mad cow disease was an isolated incident or part of a wider outbreak, as some fear.

The US agriculture department said it was broadening its investigation into how the sick animal in a Washington state farm became infected, warning that "potentially many states could be involved" in the inquiry. A second herd in Washington state, which includes a calf born to the infected cow, was yesterday put under quarantine.

British scientists had earlier confirmed the first case of mad cow disease, formally known as bovine spongiform encephalopathy, or BSE, had been discovered in the US. Japan, the biggest foreign consumer of US beef, formalised its ban on imports, raising concerns that the $40bn (£22.6bn) industry could be ruined by the discovery.

So far, more than a dozen countries have imposed bans. The Tories have called for an urgent review into whether Britain should follow suit.

A spokesman for the Food Standards Agency said only a small amount of US beef is imported into Britain, and played down the risk: "This would be muscle meat, in which no BSE infection has yet been found by scientists, but we seek further information on the situation in the US."

US workers were trying to round up the tainted beef, but officials said none of the potentially dangerous brain or spinal tissue had entered the food chain.

The infected cow, a four-year-old Holstein, had not exhibited any symptoms of the disease and was only tested because of an unrelated injury. The cow had been cleared for human consumption on December 9 before the result of the test came back on December 22. The infection was the second case of BSE in North America this year after Canada found an infected animal in May.

Ron DeHaven, the chief veterinarian of the US department of agriculture, said it could be "a matter of weeks or months" before the cause of the infection could be traced.

There were immediate calls to toughen cattle screening in the US. American inspectors have tested fewer than 30,000 of the 300 million cattle slaughtered in the past nine years and critics have warned that mad cow disease could exist undetected in the US.

The US urged calm but some of the biggest importers of US beef, including Japan, Russia, South Korea, Jordan, Vietnam, Thailand and Mexico, immediately shut their doors.