Idaho officials said an initial test has indicated one case of naturally occurring Creutzfeldt-Jakob disease, and five suspected cases are being investigated. But the officials said none of the cases is believed to have been caused by eating infected animals.

Tom Shanahan, a spokesman for the Idaho Department of Health and Welfare, said Friday that five of the cases involve people who have already died, lived in neighboring counties and were older than 60. The sixth case centered on a man, also older than 60, who lived 90 miles away and is still alive. He said officials expected to receive the results of a more in-depth second test within a week.

CJD is a rare brain-wasting disease that usually affects people in their sixties or seventies. It is not the same as the human form of mad cow disease, which is known as variant Creutzfeldt-Jakob disease and is linked to eating beef from infected cattle.

Naturally occurring CJD is found in one case per 1 million population annually, according to the Centers for Disease Control and Prevention. In a state with 1.4 million people, the fact that Idaho has so many suspected cases of the rare disease has sparked concern.