According to Idaho officials one case of Creutzfeldt-Jakob disease has been confirmed, and they are investigating five other suspected cases in the state.
Apparently none are believed to have been caused by eating infected animals.
Tom Shanahan, a spokesman for the Idaho Department of Health and Welfare, says the five cases were in one geographic area and involved people over the age of 60.
Shanahan says the cases are of the naturally occurring type of CJD and not variant.
Naturally occurring CJD is a rare brain-wasting disease in humans, that usually affects older people in their 60s or 70s, and 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.
According to the U.S. Centers for Disease Control (CDC) , it is found at a rate of about one case per one million annually.
In recent years, the United States has reported fewer than 300 cases of CJD each year, according to the CDC.
So many suspected cases of the rare disease has sparked concern among officials in a state with only 1.4 million people.
Researchers at Case Western Reserve University have confirmed that brain tissue from one woman showed CJD and caused her death. They are waiting for results from two other tests.
He says all the deaths occurred this year, beginning in February.
They are concerned, he says, because they have never had more than three cases in a year and these are in one geographic area.
The sixth suspected case involves an elderly man who has not yet died, and the disease can only be confirmed by analysing a brain sample after death.
To date investigators have been unable to pinpoint any thing that may have caused the disease and are looking at factors such as the victims' diets.
Last year, health officials found a cluster of 13 deaths due to naturally occurring CJD in New Jersey between 1988 and 1992.
According to investigators, all of those people either attended or worked at a race track in Cherry Hill, New Jersey.
The variant form of CJD is the human equivalent of bovine spongiform encephalopathy, or mad cow disease, and is contracted by people who eat beef from infected cattle.
The naturally occurring strain of CJD has no known cause.
Nevertheless both types are incurable diseases involving a malformed protein, or prion, that kills brain cells.
The United States has confirmed two cases of mad cow disease, one in a Washington state dairy animal in 2003 and the other in a Texas beef cow this year.