Borrelia that Cause Relapsing Fevers

Taxonomy and significance. The genus Borrelia belongs to the family Spir-ochaetaceae. The body louseborne epidemic form of relapsing fever is caused by the species B. recurrentis. The endemic form, transmitted by various tick species, can be caused by any of a number of species (at least 15), the most important being B. duttonii and B. hermsii.

Morphology and culture. Borreliae are highly motile spirochetes with three to eight windings, 0.3-0.6 im wide, and 8-18 im in length. They propel themselves forward by rotating about their lengthwise axis. They can be rendered visible with Giemsa stain (Fig. 4.24). It is possible to observe live bor-reliae using dark field or phase contrast microscopy.

Borrelia (Relapsing Fever, Lyme Disease) 325 — Borrelia duttonii-

Fig. 4.24 Preparation from the blood of an experimentally infected mouse. Giemsa staining.

Fig. 4.24 Preparation from the blood of an experimentally infected mouse. Giemsa staining.

Borrelia Giemsa Stain

Borreliae can be cultured using special nutrient mediums, although it must be added that negative results are not reliable.

Pathogenesis and clinical picture. B. recurrentis is pathogenic only in humans. The pathogens are transmitted by body lice. B. duttonii, B. hermsii, and other species are transmitted by ticks.

Following an incubation period of five to eight days, the disease manifests with fever that lasts three to seven days, then suddenly falls. A number of feverfree intervals, each longer than the last, are interrupted by relapses that are less and less severe. The borreliae can be detected in the patient's blood during the febrile episodes. The disease got its name from these recurring febrile attacks. The relapses are caused by borreliae that have changed their antigen structure in such a way that the antibodies produced in response to the last proliferative episode cannot attack them effectively. Bor-reliae possess a highly variable gene coding for the adhesion protein VMP (variable major protein) in the outer membrane of the cell wall.

Diagnosis. Borreliae can be detected in patients' blood when the fever rises. They cannot be reliably cultured. One method is to inject patient blood i.p. into mice. After two to three days, the mouse develops a bacteremia that can be verified by finding the pathogens in its blood under a microscope.

Therapy. The antibiotic of choice is penicillin G. Alternatives include other betalactam antibiotics and doxycycline.

Epidemiology and prevention. B. recurrentis causes the epidemic form of relapsing fever, which still occurred worldwide at the beginning of the 20th century but has disappeared for the most part today. The pathogens are transmitted by the body louse. Prevention involves eradication of the lice with insecticides.

B. duttonii, B. hermsii, and other borreliae cause endemic relapsing fever, which is still observed today in Africa, the Near and Middle East, and Central America. This is a tickborne disease. Here again, the main preventive measure is elimination of the insect vectors (ticks) with insecticides, especially in residential areas.

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  • Cornelia
    What are parasites can be observe using giemsa staining?
    6 years ago

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