Mad-Cow Case Confirmed in Washington State

Updated from 6:20 p.m. EST

The Department of Agriculture on Tuesday said it has confirmed at least one case of mad-cow disease in Washington state, but it says no tainted meat has entered the food supply.

The news immediately sparked a selloff in shares of McDonald's(MCD Quote), the world's largest consumer of beef, and other restaurant chains. In after-hours trading, McDonald's was off as much as 98 cents, or 4%, at $24.30.

Wendy's(WEN Quote) was down 90 cents, or 2.27% after hours to $38.76. ...