Mad cow disease (search), unofficial label for bovine spongiform encephalopathy (search), is a brain-wasting illness that infects cattle. Scientists believe it is spread when a cow eats meal that contains spinal or brain tissue of an animal infected with BSE.

Humans can get a related illness, variant Creutzfeldt-Jakob disease (search), if they eat meat containing infected tissue. The disease attacks the nervous system and is incurable. More than 150 people died of variant Creutzfeldt-Jakob disease in Europe after mad cow disease appeared in Britain in the 1980s and spread to several other countries.

More recently, a single cow was found infected with mad cow disease in Canada in May, prompting the United States and other countries to shut down their borders to Canadian beef imports. Scientists there concluded it was an isolated case and said meat from the infected animal did not make it into the Canadian food supply.

The United States has acted to guard against the disease. Since 1997, the Food and Drug Administration has banned animal feed that contained brain and spinal tissue of cattle. Farmers used to feed such meal to their cattle because it was high in protein and could help the animals gain weight.