stains Gram negative, not typically classified based on gram staining.
Slender and helical, with a double membrane and flexible cell wall. It is
highly motile due to flagella structure contained within the periplasmic space;
motility is key for virulence of this organism and allows it to be especially
invasive. Contains variable surface proteins (i.e. OspA/OspC).
Pathology/Infection: B. burgdorfei live in midgut of unfed
nymphal ticks. Bacteria become active during “blood meal” and switch gene
expression from OspA (quiescent) to OspC (infectious). The active microbes then
penetrate the midgut and gradually migrate to salivary glands where they are
passed to the host (mouse/human) in saliva. Process takes approximately 48 to
Tick Life cycle: Enzootic;
Hard tick (Ixodes scapularis) larvae
feed on infected mice (Peromyscus
leucopus reservoir) and mature to nymph stage. The disease carrying nymphs
can feed on uninfected mice to create a new biological reservoir. Adult feeds
and lives on Deer until replete female drops to ground and lays eggs. Humans
and dogs are incidental or dead-end hosts.
Manifestations/Disease Patterns: Infection in Human causes Lyme disease. Lyme disease progression
can be divided into the following stages –
Early disease: Erythema migrans (>80% cases) often with systemic
symptoms (fever, headaches, myalgias, etc.)
Early disseminated disease: Skin (erythema migrans),
musculoskeletal (esp. arthritis in children), neurologic (esp. aseptic
meningitis and facial nerve palsy), and/or cardiac manifestations (conduction
abnormalities) are possible.
Late disease: Recurrent arthritis of large joints (possibly
autoimmune), peripheral neuropathies and/or encephalopathy is possible.
disease is the most prevalent arthropod-borne disease in the US, with 30,000
new cases each year and an estimated 300,000 cases total per year. Cases arise
mainly in the northeastern, mid-Atlantic, and upper mid-western US.
Diagnosis is typically based on erythema migrans lesions because most patients are seronegative at presentation (false negative). Other forms of disease where erythema migrans lesions aren’t present require clinical manifestations and laboratory confirmation (ELISA + Western blot or C6 peptide test) to confirm diagnosis. Microbes can be recovered and cultured from lesions, but special expertise and growth medium are required for culture so this is rarely done clinically.
Treatment: During early disease stage, Lyme Disease is treated with tetracycline, doxycycline, amoxicillin or oral cerufoxime. For severe disease, IV ceftriaxone or penicillin is needed.
Prophylaxis: Lyme disease can be prevented by prevention of tick bites or rapid removal of ticks. Under certain conditions, single dose doxycycline (200mg) may also be effective. Until 2002, OspA was used as a vaccine; Vaccine was discontinued. Currently new vaccination products are in development.