Borrelia

ORGANISM:

GENERAL CONCEPTS:

Borreliae produce febrile diseases characterized by remittent fever.
The organisms are transmitted to humans by lice or ticks.
B. recurrentis produces epidemic relapsing fever (lice); B. hermsii causes endemic relapsing fever (ticks); B. burgdorferi is the agent responsible for Lyme disease (ticks).

DISTINCTIVE PROPERTIES:

The Borreliae are similar to Leptospira but somewhat fatter and have more complex nutritional requirements.
The cell wall contains various lipids including cholesterol.

PATHOGENESIS:

Borreliae produce a generalized infection following an incubation period of about 1 week. Symptoms include fever, headache and muscle pain that lasts 4-10 days and subsides. An afebrile period lasting 5-6 days follows and then there is a recurrence of acute symptoms.
Epidemic relapsing fever (transmitted by lice) is generally more severe than endemic relapsing fever (transmitted by ticks) and has an approximately 40% mortality if untreated. Also, the epidemic form is generally characterized by having a single relapse, while the endemic form may have several relapses due to cyclic antigenic variation of the Borrelia.
Lyme disease (transmitted by ticks) involves the production of ulcerative lesions on the skin and may lead to arthritis or neurologic involvement.

HOST DEFENSES:

Antibody is important in controlling disease because the organisms are capable of resisting non-specific defenses.

EPIDEMIOLOGY:

B. recurrentis is transmitted via the human louse. Thus, this is a disease that occurs when people are crowded together under poor conditions; i.e. war, natural disaster, etc. Humans are the reservoir for B. recurrentis.
B. hermsii is transmitted via the soft-shelled tick. This disease is maintained in (primarily) rat populations; humans acquire disease when bitten by an infected tick.
B. burgdorferi is transmitted via the hard-shelled tick (deer tick). As with B. hermsii, the organisms are maintained within animal populations and humans are an accidental host.

DIAGNOSIS:

Erythema chronicum migrans
CDC ID#9875, James Gathany

Clinical: The symptomology of the recurrent fevers is not specific enough for accurate clinical diagnosis. With Lyme disease, however, the occurrence of a "bulls-eye" lesion on the skin (erythema chronicum migrans, ECM) is almost always (85%) associated with infection. This usually begins as a small red lesion that enlarges over several weeks to a reddened area that may cover several inches in diameter. Among cases that show ECM, about 20% progress to include arthralgia, about 50% involve intermittent episodes of arthritis and 10% progress to chronic arthritis.
Laboratory: Darkfield smears can be used to observe the relapsing fever Borrelia but serologic tests (ELISA) are a better determinant for Lyme disease.

CONTROL:

Sanitary: Measures to eliminate the tick and louse vectors are important for reducing the incidence of human disease.
Immunological: A recombinant vaccine is available for Lyme disease, with a 75-90% efficacy.
Chemotherapeutic: Tetracycline is the drug of choice.
NOTE: The Centers for Disease Control (CDC) have an excellent site describing Lyme disease and Borrelia burgdorferi located at http://www.cdc.gov/ncidod/dvbid/lyme/index.htm