Bitterroot Home to Tick That Carries Bacteria for Relapsing Fever

There's important scientific news out of Rocky Mountain Laboratories in Hamilton. Scientists 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 scientific journal called "Emerging Infectious Diseases" has published a paper on it.

Dr. Tom Schwan, a Rocky Mountain Laboratories entomologist, took NBC Montana to a high-elevation wooded area on the east side of Corvallis, not far from where a man got relapsing fever in 2013. The man was bitten by a soft tick while working in his woodpile.

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," said Schwan.

He 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 the patient's woodpile. Schwan said that 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 patient became sick with tick-borne relapsing fever.

Schwan and Missoula physician Dr. Joshua Christensen, who treated the patient, wrote the paper that appears in the scientific journal.

Schwan suspected this soft tick was present in the Bitterroot before the man became ill.

"These ticks are very hard to find," he said. "They're secretive. They only come out at night."

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. Schwan and his team did a three-year study there.

"We also found evidence of the infection at Yellow Bay near the University's research station," he said.

The ticks may be elusive. But Schwan thinks they are probably native to the Bitterroot. They are widespread across the western United States.

Christensen, Schwan and his team made the important discovery that people can acquire tick-borne relapsing fever in the Bitterroot. That has never been recognized in the valley before.

"This is an important bit of evidence," Schwan said, "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."

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

He and his team have also found evidence of them in the Lake Como and Westfork areas. Both are in the southern portion of Ravalli County.

The published paper is available on the Centers For Disease Control website.