BORRELIA

Borrelia

Borrelia is a genus of spiral-shaped bacteria, known as spirochetes, that are primarily transmitted to humans through the bite of infected ticks or lice. The most notable species in this genus is Borrelia burgdorferi, the causative agent of Lyme disease, which is the most common vector-borne illness in the Northern Hemisphere. Another significant species is Borrelia recurrentis, responsible for relapsing fever.

Vectors

Borrelia recurrentis = Body louse

Borrelia spp = Soft Shelled tick

Borrelia burgdorferi = Hard Shelled tick.

Microscopic Appearance

• Spiral-shaped (spirochetes).

• Gram-negative, though not easily visualized with standard Gram staining due to their thin cell walls.

• Visualized using dark-field microscopy, silver staining, or Giemsa staining.

• Motile with endoflagella (axial filaments) located within the periplasmic space, giving them a corkscrew-like movement.

Virulence Factors

• Outer Surface Proteins (Osp):

  • Borrelia species express various Osp proteins (e.g., OspA, OspC) that play roles in adhesion to host tissues and evasion of the immune system. OspC is particularly important for early infection.

• Antigenic Variation:

  • Borrelia species can alter their surface proteins, particularly during relapsing fever, to evade the host immune response, leading to recurrent episodes of fever.

• Motility:

  • The spirochete's corkscrew-like movement helps it penetrate host tissues and disseminate throughout the body, particularly in Lyme disease.

• Endotoxin-like Activity:

  • Although Borrelia lacks classic endotoxins (LPS), it possesses lipoproteins that can trigger inflammatory responses.

Pathogenesis

• Lyme Disease (Borrelia burgdorferi):

  • B. burgdorferi is transmitted through the bite of infected Ixodes ticks (deer ticks). The bacteria enter the skin at the site of the tick bite and multiply locally before disseminating through the bloodstream to various tissues, including joints, the heart, and the nervous system.

• Relapsing Fever (Borrelia recurrentis and others):

  • Borrelia recurrentis is transmitted by the human body louse, while other species like Borrelia hermsii are transmitted by soft-bodied ticks. The bacteria multiply in the blood and undergo antigenic variation, leading to recurrent episodes of fever as the immune system struggles to eliminate the changing bacterial population.

Clinical Manifestations

• Lyme Disease:

  • Early Localized Stage:

    • Erythema migrans (EM): A characteristic "bull's-eye" rash that appears at the site of the tick bite, usually within 3-30 days. It is often accompanied by flu-like symptoms such as fever, chills, fatigue, headache, muscle, and joint aches.

  • Early Disseminated Stage:

    • Multiple EM lesions, migratory arthralgias, carditis (including heart block), and neurological symptoms such as facial palsy, meningitis, and radiculopathy.

  • Late Disseminated Stage:

    • Chronic arthritis, often affecting large joints like the knee.

    • Chronic neurological symptoms, including encephalopathy, memory problems, and neuropathy.

• Relapsing Fever:

  • Characterized by recurring episodes of high fever, chills, headache, muscle and joint pain, and nausea. Each febrile episode lasts about 3-7 days, followed by an afebrile period, then a relapse.

  • Louse-borne relapsing fever (B. recurrentis) tends to have more severe symptoms compared to tick-borne relapsing fever.

Lab Diagnosis

• Microscopy:

  • Direct visualization of Borrelia spirochetes in blood smears (Giemsa or Wright's stain) is useful in diagnosing relapsing fever, especially during febrile episodes.

• Serology:

  • In Lyme disease, serologic testing for antibodies against B. burgdorferi is common. Initial ELISA screening is followed by a confirmatory Western blot. Early in infection, serology may be negative, so clinical judgment is critical.

• PCR:

  • Detection of Borrelia DNA in blood, cerebrospinal fluid (CSF), or tissue samples can be used for diagnosis, particularly in cases of Lyme neuroborreliosis or relapsing fever.

• Culture:

  • Borrelia species are fastidious and grow slowly, so culture is not routinely used for diagnosis. Special media like Barbour-Stoenner-Kelly (BSK) are required for culture.

  • grow on complex media: Noguchi’s medium

Treatment

• Lyme Disease:

  • Early Disease:

    • Oral antibiotics such as doxycycline, amoxicillin, or cefuroxime are typically used for early Lyme disease, including cases of erythema migrans.

  • Disseminated Disease:

    • Intravenous antibiotics such as ceftriaxone or penicillin G are used for more severe manifestations, such as Lyme carditis or neuroborreliosis.

  • Post-Treatment Lyme Disease Syndrome (PTLDS):

    • Some patients may experience lingering symptoms despite appropriate treatment, often requiring supportive care, though prolonged antibiotic therapy is not typically recommended.

• Relapsing Fever:

  • Tetracyclines (e.g., doxycycline) or penicillin are effective treatments for relapsing fever.

  • Treatment should be started promptly as it may lead to a Jarisch-Herxheimer reaction, a temporary worsening of symptoms due to the release of endotoxin-like substances from dying spirochetes.

• Prevention:

  • Tick-bite prevention is key in reducing the risk of Lyme disease, including the use of repellents, protective clothing, and tick checks after outdoor activities in endemic areas.

  • No vaccine is currently available for Lyme disease, but prompt removal of attached ticks can reduce the risk of transmission.