Plague in SW Idaho ground squirrels prompts health warning

Idaho health officials say ground squirrels south of Boise have tested positive for plague and that humans and pets should avoid the area.

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

Idaho Fish and Game officials say they found 24 die-off sites. Seven dead squirrels were sent overnight to the U.S. Centers for Disease Control and Prevention, and plague confirmed on Friday morning to Idaho officials.

Officials said they routinely test ground squirrels for disease when they detect a die off in a concentrated area. Plague is not common in Idaho, but in the past it has been detected in the ground squirrel populations.

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 doesn’t reach Mountain Home.

The boundary nearly reaches Kuna in the west.

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

Veterinarian Mark Drew at Idaho Fish and Game’s Wildlife Health Laboratory said if people see symptoms such as fever, vomiting, loss of appetite or other signs of sickness in dogs or cats they should see a veterinarian immediately. He said it would be about two days for a pet to show symptoms after it’s been exposed.

So far, it’s only been found locally in ground squirrels in sagebrush habitat, he said, and not in tree squirrels or other rodents in other habitats. He added it’s still early and it’s possible they could find it in other places.

Drew also noted that while rodents with the plague is rare in Idaho, it’s an “annual occurrence” in other states.

Officials said precautions include 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 rolling on a dead ground squirrel or picking it up.

The species of ground squirrel in the area is called the Piute and is found across much of southern Idaho, said Bill Bosworth, a wildlife biologist with Fish and Game. The squirrels live in colonies that can be large with interconnected burrows, he said. He didn’t have a population estimate.

The plague is believed to have reached Idaho in about the 1930s and has likely been in the ground squirrel population for decades, Bosworth said. It’s not clear why it’s causing a die-off this year, he said. The squirrels, he said, will become dormant in mid-June when they retreat to their burrows and won’t emerge again until February.

The infected area includes the Morley Nelson Snake River Birds of Prey National Conservation Area. The large number of nesting raptors in the area is made possible, Bosworth said, because of the large population of ground squirrels active in the spring that the birds prey on. It’s not clear how susceptible raptors are to plague, he said.

Coyotes, badgers, weasels and rattle snakes also prey on the ground squirrels.

“We don’t have a lot of information on this particular species and how it responds to a plague incident like this,” Bosworth said. “There will be areas where they survive. There may be some areas where virtually all the ground squirrels succumb.”

This story was originally published May 22, 2015 at 2:04 PM.