Tick-Borne Relapsing Fever (TBRF)

What causes tick-borne relapsing fever?

TBRF is caused by several species of Borrelia bacteria, cousins of the bacterium that causes Lyme disease. In North America the main species are Borrelia hermsii, B. turicatae and B. parkeri.

They are carried by soft ticks (genus Ornithodoros). These ticks:

• Live in the nests of rodents such as chipmunks and squirrels, in cabin walls, attics and under floorboards, or in caves
• Come out at night to feed for only 15 to 90 minutes, usually less than 30
• Have a painless bite, so most people never know they were bitten

People are typically infected while sleeping in rustic cabins, especially in spring and summer when rodents have left and ticks seek new hosts, or when cabins are first opened and warmed for the season. Most US cases come from western states at higher altitudes, such as the Rocky Mountains, Sierra Nevada and Cascade ranges, and from caves in central Texas.

Other relapsing fevers

• Hard tick relapsing fever (Borrelia miyamotoi) is spread by the same blacklegged ticks that carry Lyme disease, in the Northeast and Upper Midwest.
• Louse-borne relapsing fever (Borrelia recurrentis) spreads through body lice in crowded, displaced populations, mainly in East Africa.

Why the fever relapses

The bacteria multiply in the blood, causing fever. The immune system makes antibodies that clear them, and the fever breaks. But a few bacteria switch the proteins on their surface, escaping those antibodies, and grow again a week later. Each relapse is usually milder than the last. Without treatment, people may have several episodes.

Symptoms

Symptoms begin about 7 days after the bite (range about 2 to 18 days):

• Sudden high fever, often 103°F (39.4°C) or higher
• Shaking chills and sweats
• Headache
• Muscle and joint aches
• Nausea, vomiting and abdominal pain
• Feeling very unwell, sometimes with dizziness or confusion
• Less often: rash, dry cough, eye pain, light sensitivity, jaundice

A fever episode lasts around 3 days and often ends with a "crisis": a sharp rise in temperature and pulse, followed by drenching sweats and a fall in blood pressure. A fever-free spell of about 7 days follows before the next relapse.

Complications

• Nervous system involvement: meningitis, facial nerve palsy and other cranial nerve problems, more common with some species
• Eye inflammation (uveitis) during or after illness
• Pregnancy: miscarriage, preterm birth and infection of the newborn
• Heart inflammation (myocarditis) and acute respiratory distress, rarely
• Low platelets and liver inflammation

Death is rare with treatment.

How it is diagnosed

Tell your doctor about cabin stays, caves, camping or travel in the previous few weeks.

• Blood smear: the spirochetes can often be seen under the microscope in blood taken during a fever episode. Smears taken between episodes are often negative
• PCR on blood to detect Borrelia DNA
• Antibody tests comparing samples taken weeks apart; some cross-react with Lyme tests
• Routine blood tests: low platelets, raised bilirubin and liver enzymes are common
• Lumbar puncture if there are neurological symptoms

Doctors also consider other tick-borne infections with fever, such as ehrlichiosis, Rocky Mountain spotted fever and tularemia, which need similar antibiotics but have different patterns.

Treatment

• Adults and older children: doxycycline, or tetracycline, for about 10 days
• Young children and pregnant women: penicillin or erythromycin
• Neurological involvement: intravenous ceftriaxone or penicillin, usually for 2 weeks or longer

Jarisch-Herxheimer reaction

Within 1 to 4 hours of the first antibiotic dose, many people with TBRF, often around half, develop a Jarisch-Herxheimer reaction: a sudden rise in fever, shaking chills, rapid heart rate and breathing, then a drop in blood pressure. It happens as large numbers of bacteria die and release substances that trigger inflammation. It is usually short-lived but can be severe, so the first doses are often given under medical observation, with fluids ready.

Prevention

There is no vaccine. To reduce risk:

• Choose accommodation free of rodent nests; check for droppings, nesting material or chewed openings before staying in a cabin
• Do not sleep directly against log walls; use a bed or cot away from walls
• Have cabins professionally rodent-proofed and treated before use
• Avoid sleeping in or near caves and rodent burrows
• Use insect repellent containing DEET or picaridin, though soft tick bites are hard to prevent with repellent alone
• Remove nests safely: wet them with disinfectant before cleaning to avoid other rodent infections such as hantavirus

Frequently asked questions

What are the symptoms of tick-borne relapsing fever?

The main symptoms are sudden high fevers with chills, headache, muscle and joint aches and nausea, lasting about 3 days. The fever then goes away for about a week before returning. This cycle can repeat several times without treatment.

How do you get tick-borne relapsing fever?

You get it from the bite of an infected soft tick. These ticks live in rodent nests, often in the walls and floors of rustic cabins or in caves, and bite briefly at night while you sleep. The bite is painless, so most people never notice it.

How is relapsing fever different from Lyme disease?

Both are caused by Borrelia bacteria, but relapsing fever is spread by soft ticks that feed briefly, causes repeated high fevers, and rarely causes a rash. Lyme disease is spread by hard ticks that stay attached for days, often causes a bull's-eye rash, and does not typically cause relapsing fevers.

Can tick-borne relapsing fever be cured?

Yes. A course of antibiotics such as doxycycline or penicillin cures it. The first dose can trigger a Jarisch-Herxheimer reaction with high fever and low blood pressure, so treatment often starts under medical supervision. Most people recover fully.