BOISE - Ground squirrels south of Boise have tested positive for plague, and humans and pets should avoid the area, Idaho health officials say.

The bacterial disease can be spread by the bites of fleas or by direct contact with infected animals, the Idaho Department of Health and Welfare said in a statement Friday.

"We would probably advise people not to go out in that area," said Tom Shanahan, spokesman for the agency. "If you go out there, you need to take precautions."

Officials said that includes insect repellent and staying away from dead animals. Pets should be protected with flea-repellent products and not be allowed to roam free, which increases the chances of a pet picking up or rolling on a dead ground squirrel.

Mike Keckler of Idaho Fish and Game said the agency investigated earlier this week after receiving reports of dead ground squirrels and found 24 die-off sites. Seven dead squirrels were sent overnight to the U.S. Centers for Disease Control and Prevention, he said, and researchers confirmed on Friday morning to Idaho officials that plague caused the deaths.

A map of the infected area is a circle shape extending about 45 miles south from Boise to the Snake River. The boundary also extends over Interstate 84, but it doesn't reach Mountain Home. The boundary nearly reaches Kuna in the west.

The desert area is popular in the spring, Keckler said, with a variety of outdoor enthusiasts when temperatures are cooler.

Symptoms of plague in humans include fever, chills, headache and weakness, and prompt diagnosis and treatment greatly reduces the fatality rate, officials said. The last two cases reported in Idaho, officials said, occurred in 1991 and 1992. Both patients fully recovered.

The infected area includes the Morley Nelson Snake River Birds of Prey National Conservation Area.