Borrelia miyamotoi Disease (Hard Tick Relapsing Fever)

Quick answer

Borrelia miyamotoi is a relapsing-fever bacterium spread by the same blacklegged ticks that carry Lyme disease. CDC calls the illness hard tick relapsing fever. It usually causes fever, chills, headache and aches about two weeks after a bite, rarely a rash, and standard Lyme blood tests are not designed to find it.

What Borrelia miyamotoi is

Relapsing fever is a group of infections caused by several Borrelia species that are distantly related to the Lyme bacterium. They can cause bouts of fever, headache and muscle pain lasting several days, separated by about a week of feeling well. CDC groups them by what spreads them: soft ticks, hard ticks or body lice. B. miyamotoi is the hard-tick type.

It was first found in ticks in Japan in 1995 and first identified in people in Russia in 2011. It has since been found in North America, Europe and northern Asia. CDC says it appears much less common than Lyme disease, but it is likely underrecognized because its symptoms are vague and testing is tricky.

Ticks and where it occurs

• Blacklegged (deer) tick: the upper Midwest, Northeast and mid-Atlantic.
• Western blacklegged tick: Pacific coastal states.

These hard ticks feed slowly over several days, and the longer a tick stays attached, the more likely it is to pass on the bacteria. Cases peak in August, later than Lyme disease, which peaks in late spring and early summer. The same ticks also spread Lyme and anaplasmosis; our co-infections guide compares these and others, such as babesiosis.

Symptoms

• Fever, often a single episode
• Chills or shaking
• Fatigue
• Headache
• Muscle and joint aches
• Nausea or vomiting

A 2020 study notes that the bull’s-eye-type rash of Lyme disease (erythema migrans) is uncommon with B. miyamotoi. Some people become seriously ill. CDC gives meningoencephalitis, an infection of the brain and its lining, as an example of severe disease needing hospital care, and advises specialist input for people with weakened immune systems.

Why Lyme tests can miss it

Standard Lyme blood tests look for antibodies to the Lyme bacterium, not to B. miyamotoi. In one 2020 study, none of 18 people with B. miyamotoi antibodies tested positive on a common Lyme screening test. CDC also notes the reverse can happen: relapsing fever infections sometimes cause false-positive Lyme antibody results.

Specific tests do exist, according to CDC’s clinician guidance:

• PCR on whole blood, offered by some commercial labs, can detect the bacteria early in the illness.
• Antibody tests are most reliable when the blood is drawn at least 14 days after symptoms start; early results may be negative.
• Some tests cannot tell B. miyamotoi apart from soft-tick relapsing fever, so your exposure history matters.

If you have a fever after a tick bite and a negative Lyme test, it is reasonable to ask your provider whether other tickborne infections, including this one, were considered. See our Lyme test guide and visit checklist.

Treatment

No randomized trials have tested treatments, so CDC’s guidance draws on case series using antibiotics that work for Lyme disease. Doxycycline or amoxicillin by mouth for about two weeks works for most patients, including young children, and ceftriaxone by IV is used for severe illness such as meningoencephalitis. A minority of patients have a Jarisch-Herxheimer reaction after starting treatment.

Prevention

CDC advises using EPA-registered repellents, avoiding wooded and brushy areas with high grass and leaf litter, and checking your body, clothing and pets for ticks after being outdoors. More tips are in our prevention guide, and spotting symptoms early is step 3 of our plan, recognize the signs.

Frequently asked questions