Tick-borne relapsing fever (TBRF) is an infection caused by certain species of Borrelia bacteria, which can be transmitted by tick bite. The main symptoms of TBRF are high fever, headaches, and muscle and joint aches. Symptoms can recur repeatedly if the infection is not treated, with cycles of 2-7 days of illness alternating with 4-14 days of recovery. Without antibiotic treatment, this cycle can repeat several times.
In the United States, cases of tick-borne relapsing fever (TBRF) are usually due to Borrelia hermsii, but other bacteria species can also cause TBRF. Most people with TBRF are infected in rural, mountainous areas of the western United States where the ticks that can carry B. hermsii live. Large TBRF outbreaks have been linked to rustic cabins near national parks.
TBRF occurs worldwide. In the United States, most people become infected after overnight stays in rural, rodent-infested cabins in mountainous areas of the western states. Most cases of TBRF in the US, and specifically in Washington State, are transmitted by the soft tick, Ornithodoros hermsi, which is associated with rodents found in coniferous forests at higher elevations (usually 1500-8000 feet). TBRF is the most commonly-reported tick-borne disease acquired in Washington State; the majority of the cases are reported from the eastern slopes of the Cascades and the northeastern corner of the state.
The other two species of tick that transmit TBRF in the US, O. parkeri and O. turicata, are usually found at lower altitudes in the Southwest.
TBRF infections typically occur in the summer months between May and September; but people can become infected year-round and sometimes within their primary homes, not just rustic cabins.
People can only get TBRF if they are bitten by an infected tick. TBRF is not spread directly to humans from animals or from one person to another. The ticks that can transmit TBRF are called "soft ticks" and are different from "hard ticks" that transmit other diseases such as Lyme disease, Rocky Mountain spotted fever, and tularemia. Soft ticks tend to bite for much shorter periods of time, typically less than 30 minutes, and usually at night. They live within rodent nests and burrows, rather than grassy or bushy areas. Soft ticks prefer to feed on rodents, but may seek out humans if rodents are scarce. Their bites are painless, and most people don't realize that they have been bitten.
The soft ticks that can transmit TBRF are within the Ornithodoros genus. They become infected with Borrelia bacteria by feeding on infected wild rodents. Once infected, the ticks remain infected for the rest of their lifespan, which can be up to 10 years.
Most people who are infected first get sick about 7 days (range, 2 to 18 days) after they are bitten by an infected tick. Symptoms typically include high fever (e.g., 103⁰ F), along with shaking chills, headaches, muscle or joint aches, nausea, vomiting, and possibly rash. The illness characteristically cycles between 2-7 days of fever and 4-14 days without fever. This cycle may repeat many times, over several weeks, if the person is not treated.
If you or your family member develops symptoms of relapsing fever, visit your healthcare provider or contact your local health department. Untreated TBRF can cause serious complications, especially if infection occurs during pregnancy. Approximately 5-10% of untreated cases are fatal.
The most important action you can take is to educate yourself about where and how you are likely to be exposed to TBRF. Be aware of the potential risks when visiting or camping in mountain forests:
Check sleeping areas for evidence of rodents - holes in the floor or walls, shredded material from mattresses, and rodent droppings on counters or in cupboards. Avoid sleeping in rodent-infested buildings whenever possible. Avoid vacuuming, sweeping, or stirring up dust in and around rodent-contaminated areas to prevent hantavirus pulmonary syndrome, a rare, but potentially fatal respiratory disease. If the dwelling has been unoccupied, change and wash all bedding before use.
If you cannot avoid sleeping in a rodent-infested building, pull beds away from touching any walls.
- If you are renting a cabin and notice a rodent infestation, contact the owner to alert them.
- If you own a cabin or other structure with a rodent infestation, consult a licensed pest control professional who can safely:
- Identify and remove any rodent nests from walls, attics, crawl spaces, and floors.
- Treat cracks and crevices in the walls with pesticide to remove ticks.
- Establish a pest control plan to keep rodents out.
- Use EPA-registered insect repellent to prevent tick bites.
- Rodent-proof cabins, homes, and other buildings in areas where the disease is known to occur. Learn more about avoiding attracting rodents and sealing up your home on our page about rodent control.
Pesticide control of ticks in an infested building may be necessary for comprehensive prevention of TBRF. Eliminating rodents without tick control may actually increase the risk of people becoming infected, because hungry ticks will seek out other mammals (including humans) on which to feed if rodents are unavailable. Contact a licensed professional exterminator or pest controller to discuss appropriate tick control measures for your dwelling.