Borrelia spp. also can cause relapsing fever. Two of the most common species are B. recurrentis, which causes epidemics of louseborne relapsing fever, and B. hermsii, which causes tickborne relapsing fevers. These Borrelia species are transmitted by the body louse Pediculus humanus and the soft-bodied tick Ornithodoros hermsi, respectively. Lice acquire the spirochetes from human reservoirs, whereas ticks acquire them from rodent reservoirs. Spirochetes infect humans when Borrelia in the vector’s saliva or excreta enter the skin rapidly as the vector bites.

In both louse- and tickborne relapsing fevers, bacteremia usually occurs after the initial exposure, leading to a sudden high fever (39–43 °C [102.2–109.4 °F) typically accompanied by headache and muscle aches. After about 3 days, these symptoms typically subside, only to return again after about a week. After another 3 days, the symptoms subside again but return a week later, and this cycle may repeat several times unless it is disrupted by antibiotic treatment. Immune evasion through bacterial antigenic variation is responsible for the cyclical nature of the symptoms in these diseases.

The diagnosis of relapsing fever can be made by observation of spirochetes in blood, using darkfield microscopy. For louseborne relapsing fever, doxycycline or erythromycin are the first-line antibiotics. For tickborne relapsing fever, tetracyclineor erythromycin are the first-line antibiotics.

Relapsing fever is bacterial infection that can cause recurring bouts of fever, headache, muscle and joint aches, and nausea. There are three types of relapsing fever:

• Tick-borne relapsing fever (TBRF)
• Louse-borne relapsing fever (LBRF)
• Borrelia miyamotoi disease (sometimes called hard tick relapsing fever)

TBRF occurs in the western United States and is usually linked to sleeping in rustic, rodent-infested cabins in the mountains. In Texas, TBRF is frequently linked to cave exposures. LBRF is transmitted by the human body louse and usually occurs in refugee settings in developing parts of the world. Borrelia miyamotoi disease occurs in the same places where Lyme disease is found and is transmitted by the blacklegged tick.

LBRF is caused by a spiral-shaped bacteria, Borrelia recurrentis, which is transmitted from human to human by the body louse. LBRF outbreaks most commonly occur in conditions of overcrowding and social disruption.

LBRF epidemics occurred frequently in Europe during the early 20th Century. Between 1919 and 1923, 13 million cases resulting in 5 million deaths occurred in the social upheaval that overtook Russia and eastern Europe. During World War II, a million cases occurred in North Africa.

Today, LBRF causes sporadic illness and outbreaks in sub-Saharan Africa, particularly in regions affected by war and in refugee camps. LBRF is commonly found in Ethiopia, Sudan, Eritrea, and Somalia. Illness can be severe, with mortality of 30 to 70% in outbreaks.

What is Borrelia miyamotoi?

Borrelia miyamotoi is a type of spiral-shaped bacteria that is closely related to the bacteria that cause tickborne relapsing fever (TBRF). It is more distantly related to the bacteria that cause Lyme disease. First identified in 1995 in ticks from Japan, B. miyamotoi has since been detected in two types of North American ticks, the blacklegged or “deer” tick (Ixodes scapularis) and the Western blacklegged tick (Ixodes pacificus). These ticks are already known to spread the germs that cause several diseases, including Lyme disease and anaplasmosis.

What are the symptoms of B. miyamotoi disease?

In a 2015 study of patients with this infection, the most common symptoms were fever, chills, and headache. Other common symptoms included body and joint pain and fatigue. Rash was uncommon, with fewer than 1 in 10 patients developing a rash.

What type of testing is available for patients who might be infected?

Healthcare providers can order blood tests to determine if a person may be infected with B. miyamotoi. Two types of laboratory tests are available:

• Polymerase chain reaction (PCR) tests that detect DNA from the bacteria
• Serologic tests that detect antibodies made by the body in response to infection

CDC also provides laboratory diagnostic support for B. miyamotoi infections at the request of state health departments.

How is B. miyamotoi treated?

B. miyamotoi infections are treated with a 2- to 4-week course of the antibiotic doxycycline. Amoxicillin and ceftriaxone have also been successfully used.

What more do researchers need to know?

Since this is a relatively new and rare disease in the United States, researchers and healthcare providers are working to answer basic questions including:

• What are the signs and symptoms of illness?
• Where is B. miyamotoi found?
• How common is infection?
• Who is at greatest risk for infection?

What is CDC doing?

CDC is working to:

• Detect and track cases in people.
• Determine where B. miyamotoi is found and how common infection is.
• Analyze blood samples for B. miyamotoi and other tickborne germs using advanced molecular detection methods.

How can I avoid this disease?

Reducing exposure to ticks is the best defense against tickborne infections.

What can I do to prevent TBRF?

• Avoid sleeping in rodent-infested buildings whenever possible. Although rodent nests may not be visible, other evidence of rodent activity (e.g., droppings) are a sign that a building may be infested.
• Prevent tick bites. Use insect repellent containing DEET (on skin or clothing) or permethrin (applied to clothing or equipment).
• If you are renting a cabin and notice a rodent infestation, contact the owner to alert them.
• If you own a cabin, consult a licensed pest control professional who can safely:
  • Identify and remove any rodent nests from walls, attics, crawl spaces, and floors. (Other diseases can be transmitted by rodent droppings—leave this job to a professional!)
  • Treat “cracks and crevices” in the walls with pesticide.
  • Establish a pest control plan to keep rodents out.
• Pest Control Professionals and Public Health Departments: Remove rodents and nests, stop rodents from reentering buildings, and reduce exposure to infected ticks

Why shouldn't I remove the nests myself?

Activities that put you in contact with deer mouse droppings, urine, saliva, or nesting materials can place you at risk for infection with Hantavirus Pulmonary Syndrome (HPS), a potentially fatal condition. Hantavirus is spread when virus-containing particles from deer mouse urine, droppings, or saliva are stirred into the air. Infection occurs when you breathe in virus particles.

TBRF is found in discrete areas throughout the world, including mountainous areas of North America, plateau regions of Mexico, Central and South America, the Mediterranean, Central Asia, and much of Africa.

In the United States, TBRF occurs most commonly in 14 western states: Arizona, California, Colorado, Idaho, Kansas, Montana, Nevada, New Mexico, Oklahoma, Oregon, Texas, Utah, Washington, and Wyoming.

TBRF is spread by multiple tick species, each of which has a preferred habitat and set of hosts. Ornithodoros hermsi, the tick responsible for most cases in the United States, prefers coniferous forests at altitudes of 1500 to 8000 feet where it feeds on tree squirrels and chipmunks. The two other U.S. tick species that transmit TBRF, O. parkeri and O. turicata, are generally found at lower altitudes in the Southwest, where they inhabit caves and the burrows of ground squirrels, prairie dogs, and burrowing owls.

Most TBRF cases occur in the summer months when more people vacationing and sleeping in rodent-infested cabins. Nevertheless, TBRF can also occur in the winter months. Fires started to warm a cabin are sufficient to activate ticks resting in the walls and woodwork.

Clinical Disease

Tick-borne relapsing fever (TBRF) is a rare infection linked to sleeping in rustic cabins, particularly cabins in mountainous areas of the western United States. The main symptoms of TBRF are high fever (e.g., 103° F), headache, muscle and joint aches. Symptoms can reoccur, producing a telltale pattern of fever lasting roughly 3 days, followed by 7 days without fever, followed by another 3 days of fever. Without antibiotic treatment, this process can repeat several times.

Borrelia bacteria that cause TBRF are transmitted to humans through the bite of infected “soft ticks” of the genus Ornithodoros. Soft ticks differ in two important ways from the more familiar “hard ticks” (e.g., the dog tick and the deer tick). First, the bite of soft ticks is brief, usually lasting less than half an hour. Second, soft ticks do not search for prey in tall grass or brush. Instead, they live within rodent burrows, feeding as needed on the rodent as it sleeps.

Humans typically come into contact with soft ticks when they sleep in rodent-infested cabins. The ticks emerge at night and feed briefly while the person is sleeping. The bites are painless, and most people are unaware that they have been bitten. Between meals, the ticks may return to the nesting materials in their host burrows.

There are several Borrelia species that cause TBRF, and these are usually associated with specific species of ticks. For instance, B. hermsii is transmitted by O. hermsi ticks, B. parkerii by O. parkeri ticks, and B. turicatae by O. turicata ticks. Each tick species has a preferred habitat and preferred set of hosts:

• Ornithodoros hermsi tends to be found at higher altitudes (1500 to 8000 feet) where it is associated primarily with ground or tree squirrels and chipmunks.
• Ornithodoros parkeri occurs at lower altitudes, where they inhabit caves and the burrows of ground squirrels and prairie dogs, as well as those of burrowing owls.
• Ornithodoros turicata occurs in caves and ground squirrel or prairie dog burrows in the plains regions of the Southwest, feeding off these animals and occasionally burrowing owls or other burrow- or cave-dwelling animals.

Soft ticks can live up to 10 years; in certain parts of the Russia the same tick has been found to live almost 20 years. Individual ticks will take many blood meals during each stage of their life cycle, and some species can pass the infection along through their eggs to their offspring. The long life span of soft ticks means that once a cabin or homestead is infested, it may remain infested unless steps are taken to find and remove the rodent nest.