Possible plague found in Canyon County rodents: Vole deaths near Caldwell prompt testing for plague bacteria

Initial testing of dead voles (commonly called meadow mice) found in an area near Highway 19 immediately west of Caldwell indicates possible plague. The mortality event appears to be localized and not widespread; however Idaho public health officials and the Idaho Department of Fish and Game are urging people to take precautions and report groups of dead rodents.

A vole. Photo by Evan James hymo/Wikipedia
A vole. Photo by Evan James hymo/Wikipedia

In May, ground squirrels tested positive for plague in an area southeast of Boise. Idaho Department of Fish and Game and Idaho public health officials don’t believe there is any connection between the two events.

Plague is a bacterial disease of rodents that can cause serious illness to people and pets if not treated quickly. Plague is generally transmitted to humans and animals through bites of infected fleas. It may also be transmitted by direct contact with infected animals, including rodents, rabbits, and pets. Common rodents that can become infected include mice, rats, voles, chipmunks, and ground squirrels. Tree squirrels in Idaho are not known to carry plague.

Plague activity can increase in the spring and summer months when rodents are more active. People can be exposed to plague when pets have contact with rodents or fleas outdoors, or bring infected rodents or fleas back into the home. People can also become infected by caring for a sick pet without proper precautions.

People can greatly reduce their risk of becoming infected with plague by taking simple precautions, including avoiding contact with wild rodents, their fleas and rodent carcasses. They should not feed rodents in parks, picnic or campground areas and never handle sick or dead rodents. Health officials recommend:

  • See your doctor about any unexplained illness involving a sudden and severe fever.
  • Keep your pets from roaming and hunting voles or other rodents. Sick pets should be examined promptly by a veterinarian, especially if they may have had contact with sick or dead rodents.
  • Talk to your veterinarian about using an appropriate flea control product on pets. Not all products are safe for cats, dogs or children.
  • Don’t leave pet food and water where rodents or other wild animals can access them.
  • Clean up areas near your home where rodents can live, such as woodpiles and lots with tall grasses and weeds.
  • Put hay, wood, and compost piles as far as possible from your home.

Symptoms of plague in humans include sudden onset of fever, chills, headache, and weakness. In most cases there is a painful swelling of the lymph node in the groin, armpit or neck areas. Plague symptoms in cats and dogs are fever, lethargy and loss of appetite. There may be a swelling in the lymph node under the jaw. With prompt diagnosis and appropriate antibiotic treatment, the fatality rate in people and pets can be greatly reduced. Physicians who suspect plague should promptly report it to their local public health district.

Plague is a naturally occurring bacterium in Idaho’s rodent populations. USDA Wildlife Services tested various species of animals that eat rodents between 2005 and 2010 for the presence of antibodies to plague. Just 18 animals tested positive, primarily badgers and coyotes, indicating past exposure to plague that was likely from infected rodents. People are encouraged to avoid direct contact with dead or sick voles, or other rodents. If you find groups of dead rodents do not touch them, but report the location through the Idaho Department of Fish and Game website at: fishandgame.idaho.gov/content/plague

Since 1940, only five human cases of plague have been reported in Idaho. The last two cases reported in Idaho occurred in 1991 and 1992, with both patients fully recovering.

Map of affected area
Map of affected area

For more information:

Editors: For public health questions:

Southwest District Health
Laurie Boston
Public Information Officer
(208) 455-5325
Idaho Dept. of Health & Welfare
Tom Shanahan
Public Information Officer
(208) 334-0668

For questions about the affected area or animal infections:

Idaho Fish and Game
Mike Keckler
Bureau Chief for Communications
(208) 287-2870

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