Updated at 5:33 p.m.

An Idaho child is in recovery after he contracted bubonic plague. Now health authorities are investigating whether the child picked up the rare infectious disease in Oregon or at home.

Bubonic plague is passed through infected fleas. So it is possible the child was bitten on a recent trip to Oregon. The disease can also be passed through contact with an animal that was bitten by a flea.

It was known as "Black Death" when it killed millions of Europeans in the Middle Ages. And though the plague can pass between humans, it is rare, according to health authorities.

Since 1990, eight people have been diagnosed with bubonic plague in Oregon. Two were found in Idaho. Though the disease can be deadly, it is treatable if caught early.

The child lives in Elmore County, where ground squirrels tested positive for bubonic plague in 2015 and 2016. The Idaho Central District Health Department said it found no traces of the disease in squirrels tested this year.

The plague shows up within two to six days of exposure. The symptoms include sudden fever, chills, headaches and weakness. Usually, lymph nodes swell in the groin, armpit or neck.

About 11 percent of bubonic plague cases in this country are fatal, according to the U.S. Centers for Disease Control and Prevention. Advances in antibiotics have significantly increased the chance of survival since 1941, when there was a 66 percent chance of death.

Pets will show symptoms if infected. Cats and dogs might also become feverish, have lethargy or a loss of appetite, and the lymph nodes under the jaw will swell.

The Central District Health Department recommends people wear insect repellent, long pants and socks when visiting a plague-ridden area.

The agency also advises pet owners to ensure their animals are protected from fleas and don't hunt rodents. When a host animal dies, the fleas will leave and look for the next available host, so don't handle wild rodents or dead ones.

-- Molly Harbarger

mharbarger@oregonian.com

503-294-5923

@MollyHarbarger