Last month, the U.S. Department of Agriculture (USDA) reported the first case of mad-cow disease in the country. Officials investigated the case and took steps to protect the nation's beef supply. The USDA banned the use of sick animals in food.
The sick cow was brought to Washington state from Canada. By last week, three herds in the state had been quarantined, or isolated, in case they have the disease.
Mad-cow disease, or bovine spongiform encephalopathy, is carried in a cow's brain and spinal cord. The USDA says the risk to humans is very low. Still, more than 30 nations have banned the sale of U.S. beef. And the U.S. will continue its ban on beef and live cattle from Canada.