Lyme disease (named after a town in Connecticut) or Lyme borreliosis is a vector-borne zoonotic disease caused by three genomospecies of Borrelia, collectively referred to as Borrrelia burgdorferi and rarely by Borrelia mayonii. Infected black-legged ticks are the vectors of Lyme disease.
Lyme disease is the most common tick-borne disease in the United States. It is also the most common vector-borne disease in the United States, with approximately 20,000 reported cases to CDC each year.
Table of Contents
Characteristics of Borrelia burgdorferi
Borrelia burgdorferi is a helical-shaped spirochete that is poorly gram-stained (other spirochetes do not take up Gram stain). The cells stain a weak Gram-negative as safranin is the last dye used, but Borrelia burgdorferi is not classified as either Gram-positive or Gram-negative.
Borrelia can be stained with Giemsa stain or other blood stains and can be seen in the standard light microscope. It is better viewed under a dark ground microscope or by silver impregnation staining. The ultrastructure of Borrelia is similar to Treponema and Leptospira, with minor differences.
- Size: Larger, 10-30 μm in length (longer than a human red blood cell, which is 7 μm in diameter) and 0.2-0.5 μm in width.
- Spirals: They are less in number (3-10 μm) with wider spirals (3 μm) and longer amplitude (2 μm)
- Endoflagella: More in number (7-11), attached subterminally at the pole.
Transmission
Rodents and deer are the main reservoirs of Lyme disease. It is widespread in the USA and reported in other parts of the world.
Related disease: Relapsing Fever: Etiology, Pathogenesis, Lab Diagnosis
Lyme disease is transmitted by the bite of black-legged tick (Ixodes scapularis or Ixodes pacificus ). All three stages of ticks (i.e. larval, nymphal, and adult stages) can transmit the infection, but it is thought that nymphs infect more humans than adult ticks because they are so hard to see (<2 mm).
Borrrelia burgdorferi expresses outer-surface protein A (OspA) in the midgut of the tick which is required for its survival in tick. When the bacterium reaches the salivary gland of the tick, it expresses protein OspC that binds to a tick salivary gland protein (Salp15). This attachment is crucial for transmission.
There is no evidence of person-person transmission of Lyme disease. There is no credible evidence that Lyme disease can be transmitted through air, food, water, or from the bites of mosquitoes, flies, fleas, or lice.
The tick must attach at least 24 hours for transmission. Removing a tick quickly (within 24 hours) can greatly reduce the chance of getting Lyme disease.
Clinical Manifestations
If left untreated, Lyme disease can produce a wide range of symptoms, depending on the stage of infection. These include fever, rash, facial paralysis, and arthritis.
Stage 1: Early localized infection
After an incubation period of 3-32 days, an annular maculopapular lesion develops at the site of the tick bite called erythema migrans, commonly involving the thigh, groin, and axilla. It may be absent in 20% of cases. Classic erythema migrans rash appears as “bull’s-eye.”
(Image source)
Stage 2: Early disseminated infection
If untreated, B. burgdorferi spreads hematogenously to many sites within days or weeks, resulting wider range of symptoms. These symptoms usually appear weeks or months after infection and can include:
- Secondary annular skin lesions (more or larger rashes covering more parts of the body)
- Musculoskeletal pain (arthralgia)
- Profound malaise and fatigue
- Bell’s palsy (facial paralysis)
Neurological abnormalities occur in 15% of cases, including meningitis, encephalitis, and typical lymphocytic meningoradiculitis seen in cases from Europe and Asia, called Bannwarth syndrome. Cardiac involvement occurs in 8% of cases, including atrioventricular block.
Stage 3: Late persistent infection (Lyme arthritis)
Late disseminated Lyme disease symptoms can appear months or even years after infection. Symptoms in this later stage of infection are more severe and include:
- Frank arthritis involves large joints (especially the knees), lasting for weeks or months in a given joint.
- Inflammation of the heart
- Inflammation of the brain, etc.
Laboratory Diagnosis
The sample depends on the clinical presentations and may include blood, CSF, or scrapping from skin lesions.
Culture
Isolation of B. burgdorferi can be done by culturing specimens like skin lesions, blood, or CSF in a special BSK medium (Barbour-Stoenner-Kelly). Cultures are incubated at 34oC and examined under a dark field microscope weekly for two months.
Serology
it is the principal method of diagnosis of Lyme disease. In the first month of infection, both IgM and IgG are detected. As the disease proceeds, IgM disappears and IgG response predominates.
- A four-fold rise in titer at 2-3 weeks intervals is more significant.
- ELISA and western blot formats are available for separate detection of IgG and IgM.
Earlier, CDC recommended performing an ELISA first and if found positive or equivocal, it has to be confirmed by IgM and/or IgG immunoblots. This standard two-tiered testing (STTT) algorithm for Lyme disease serology is replaced by a modified two-tiered testing (MTTT) algorithm that employs two enzyme immunoassays (EIAs)
Molecular methods
PCR detecting specific DNA is much superior to culture for detecting B. burgdorferi in joint fluid, but its sensitivity is poor for CSF, blood, or urine samples. PCR-RFLP of the intergenic rrf-rrl region has been used for genomospecies detection.
References and further readings
- Microbe Wiki, Borrelia burgdorferi
- Performance of a Modified Two-Tiered Testing Enzyme Immunoassay Algorithm for Serologic Diagnosis of Lyme Disease in Nova ScotiaIan R. C. Davis, Shelly A. McNeil, Wanda Allen, Donna MacKinnon-Cameron, L. Robbin Lindsay, Katarina Bernat, Antonia Dibernardo, Jason J. LeBlanc, Todd F. HatchetteJournal of Clinical Microbiology Jun 2020, 58 (7) e01841-19; DOI: 10.1128/JCM.01841-19
- Lyme disease. Center for Disease Control and Prevention.
- Bay Area Lyme Foundation
