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Bitterroot Valley ticks can cause relapsing fever, lab finds

The Bitterroot Mountains are seen near Hamilton, Mont., in the fall of 2002. (FILE)
The Bitterroot Mountains are seen near Hamilton, Mont., in the fall of 2002. (FILE)
Associated Press

HAMILTON, Mont. – Scientists at Rocky Mountain Laboratories have discovered the Bitterroot Valley is home to a tick that carries the bacteria that causes relapsing fever.

Relapsing fever is a treatable, acute, usually nonfatal disease that can make patients sick over and over again. If not treated, it can be fatal to the fetus of a pregnant woman.

A paper about the Bitterroot tick was published recently in the scientific journal Emerging Infectious Diseases.

The soft tick is different from the larger hard-shelled tick that causes Rocky Mountain spotted fever.

“You don’t pick them up while hiking through the woods,” Tom Schwan, a Rocky Mountain Laboratories entomologist, told KECI-TV.

Schwan, who co-wrote the paper with a Missoula doctor, said the ticks feed much more quickly than the Rocky Mountain spotted fever tick.

“Most people don’t know when they’re being bitten by these ticks,” he said.

He said chipmunks and squirrels are hosts to the tick.

In 2013, his team of scientists took blood samples from a chipmunk that was trapped near where a man got relapsing fever. The man was bitten by a soft tick while working in his woodpile.

Schwan said the chipmunk was infected with the same bacteria that the man who fell ill was infected with.

He said finding the infected chipmunk, plus infected ticks in the woodpile, explained how the man became sick with tick-borne relapsing fever.

“This is an important bit of evidence to help in the future when people get infected with this disease, so they can get the proper diagnosis and prompt treatment with the appropriate antibiotics,” Schwan said.

The scientist thinks these ticks may be fairly widespread in the valley.

In 2002, Schwan and his team found soft ticks on Wild Horse Island on Flathead Lake. Five people attending a family reunion there were bitten by the ticks and came down with relapsing fever.

“We also found evidence of the infection at Yellow Bay near the university’s research station,” he said.

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