Borrelia hermsii is a spiral-shaped bacterium, or spirochete, that causes tick-borne relapsing fever (TBRF) in humans. This microorganism is a public health concern, particularly in specific geographic areas, due to its ability to cause recurring episodes of illness.
Understanding Borrelia hermsii and Its Disease
Borrelia hermsii is a spirochete bacterium, characterized by its spiral shape. It is a primary agent of tick-borne relapsing fever (TBRF) in North America, specifically in the western United States and southern British Columbia, Canada. The disease is notable for its “relapsing” nature, where symptoms, particularly fever, recur after periods of apparent recovery.
The characteristic relapsing fever pattern occurs because Borrelia hermsii undergoes antigenic variation, a process where the bacterium changes its surface proteins. This allows it to evade the host’s immune system, leading to repeated cycles of bacterial multiplication in the blood and subsequent febrile episodes. This mechanism differentiates TBRF from other tick-borne illnesses like Lyme disease, which involves a single, prolonged episode of illness.
Transmission Pathways
Borrelia hermsii is primarily transmitted to humans through the bite of the soft-bodied tick, Ornithodoros hermsi. Unlike hard-bodied ticks that remain attached for days, these soft ticks feed rapidly, usually for less than 30 minutes. Their bites are often painless, meaning most infected people do not find a tick on themselves.
These ticks commonly inhabit rodent burrows and nests, feeding on rodents while they sleep. Human infections often occur when individuals stay overnight in rustic cabins, especially those infested with rodents, in mountainous regions. Ticks emerge at night from cracks in walls, floors, or attics to feed on sleeping individuals. Exposure is most common in summer, but can also happen in winter if heating a cabin activates resting ticks.
Recognizing the Symptoms
Symptoms of tick-borne relapsing fever caused by Borrelia hermsii appear about 3 to 12 days after exposure to an infected tick. The illness is characterized by abrupt onset of high fever, often reaching 39°C to 43°C (102°F to 109°F), accompanied by shaking chills, severe headache, muscle aches, and joint pain. Nausea, vomiting, and fatigue are also common symptoms during these febrile periods.
A hallmark of this infection is the cyclical pattern of symptoms. A fever episode lasts for 1 to 3 days, followed by an afebrile period of 4 to 14 days where the patient may feel well or experience general malaise. Without antibiotic treatment, these cycles can repeat, with symptoms returning in successive relapses, although subsequent episodes may be less severe. Untreated cases can lead to severe complications, including jaundice, an enlarged liver or spleen, myocarditis, and acute respiratory distress syndrome (ARDS).
Diagnosis and Treatment Approaches
Diagnosis of Borrelia hermsii infection begins with recognizing the characteristic recurring fever pattern and considering the patient’s exposure history, particularly if they have stayed in rodent-infested cabins in endemic areas. Confirmation relies on laboratory tests, especially direct visualization of spirochetes. During febrile episodes, microscopic examination of blood smears, using stains like Wright or Giemsa, can reveal the spiral-shaped bacteria. Darkfield or brightfield microscopy can also be used, and acridine orange stain is considered more sensitive.
Molecular tests, such as polymerase chain reaction (PCR), can also detect Borrelia DNA in blood samples, especially during the symptomatic phase. While serologic tests are considered unreliable for diagnosing relapsing fever, PCR offers a sensitive method for detecting the pathogen’s genetic material. Prompt treatment is important to prevent complications and reduce the risk of mortality, which can be 4-10% in untreated cases.
Treatment for Borrelia hermsii infection primarily involves antibiotic therapy. Doxycycline is a commonly used antibiotic, and erythromycin, penicillin, chloramphenicol, or ceftriaxone may also be effective. A single dose of doxycycline is sufficient. Supportive care, such as managing fever and pain, is also provided. Patients may experience a Jarisch-Herxheimer reaction within a few hours of initial antibiotic treatment, characterized by chills, fever, increased heart rate, and low blood pressure, which is a known response to the rapid killing of spirochetes.
Prevention Strategies
Preventing Borrelia hermsii infection primarily involves avoiding contact with the soft-bodied ticks that transmit the bacterium. Individuals should be cautious when visiting or sleeping in rustic cabins or other structures, especially in mountainous regions where infected ticks and their rodent hosts are common. Before staying in such accommodations, inspect for signs of rodent infestation and seal any potential entry points for rodents.
Using insect repellents containing DEET or permethrin on clothing and gear can help deter ticks. Permethrin can be applied to boots, clothing, and camping equipment and remains effective through several washes. After spending time outdoors in wooded, brushy, or grassy areas, a thorough body check for ticks is recommended. Showering within a few hours of returning indoors can also help wash off unattached ticks.