78. Genus Borrelia. Causative agents of recurrent typhus. Causative agents of Lyme borreliosis.
Covers the general features of Borrelia as motile, Gram-negative spirochetes and how the two named species, B. recurrentis and B. burgdorferi, are transmitted by lice and ticks respectively. It then takes pathogenesis, the clinical stages of Lyme borreliosis and recurrent typhus, diagnostic methods including microscopy, serology, PCR and culture, and treatment and prevention. A side-by-side comparison table of the two species closes the note.
Topic 78 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 8 sections, about 505 words (4 min of reading), with 15 flashcards.
In this note
Genus Borrelia: Causative Agents of Recurrent Typhus and Lyme Borreliosis
General Features:
Pathogenesis:
Diseases:
Diagnosis:
Treatment:
Prevention:
Comparison: Borrelia burgdorferi vs Borrelia recurrentis
General Features:
Gram Staining: Borrelia are Gram-negative spirochetes.
Shape: Spiral or corkscrew-shaped with a flexible, thin body.
Motility: Highly motile, with a characteristic "corkscrew" motion due to axial filaments (flagella-like structures located between the cell wall and outer membrane).
Transmission:
Borrelia recurrentis (causing recurrent typhus) is transmitted by body lice (Pediculus humanus).
Borrelia burgdorferi (causing Lyme disease) is transmitted by ticks, particularly Ixodes scapularis in North America.
Pathogenesis:
1. Entry:
In Lyme disease, Borrelia burgdorferi enters the human body through the bite of an infected tick.
In recurrent typhus, Borrelia recurrentis enters through the bite of a body louse.
2. Colonization:
In Lyme disease, the bacteria migrate to various tissues, including the skin, heart, joints, and nervous system.
In recurrent typhus, Borrelia invades blood vessels, primarily leading to bacteremia.
3. Virulence factors:
Outer surface proteins (OSPs): These proteins allow Borrelia to evade the host immune system by altering their surface antigens. This antigenic variation is a hallmark of recurrent infection in Borrelia species.
Lipopolysaccharides (LPS): Borrelia has a unique LPS, which lacks the endotoxin properties of other Gram-negative bacteria, making it less inflammatory.
Flagella: The flagella of Borrelia are located in the periplasmic space, contributing to its motility and allowing it to penetrate tissue barriers.
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