Spirochetes appear as spiral and curved bacteria. The four genera of spiral and curved bacteria—Borrelia, Treponema, Leptospira, and Spirillum (Table 7.6)—include several human pathogens. Most spirochetes multiply within a living host. Pathogenic Treponema organisms are transmitted from person to person through direct contact. Borrelia pass through an arthropod vector. Leptospira are usually contracted accidentally by humans through water contaminated with animal urine or a bite by an infected animal.

1. Obtain a 2-mL blood specimen in a red-topped tube.

2. For Lyme disease, a two-step process is used. The first step uses either ELISA or IFA. A second step, using a Western blot test, is performed to confirm a positive ELISA or IFA result. If the Western blot is negative, it suggests that step 1 was a false positive. (Ten proteins are used in the serodiagnosis of Lyme disease.)

1. Borrelia appear in the blood at the onset of relapsing fever. Louse-borne relapsing fever is caused by Borrelia recurrentis, tick-borne relapsing fever by several other Borrelia species, and Lyme disease by Borrelia burgdorferi. To date, there is no evidence that Lyme disease is transmitted by person-to-person contact.

2. Treponema (Borrelia) vincentii is the species responsible for ulcerative gingivitis (trench mouth).

   1. T. pallidum subsp. pallidum causes venereal syphilis in humans.

   2. T. pallidum subsp. pertenue causes yaws (a chronic skin disease affecting children younger than 15 years in poverty-stricken areas).

   3. Treponema carateum causes pinta (also known as carate, a chronic, nonvenereal infection spread through contact with open skin).

   4. T. pallidum subsp. endemicum causes bejel (nonvenereal syphilis).

3. Leptospira is the genus of microorganism responsible for Weil disease (infectious jaundice), swamp fever, swineherd’s disease, and canicola fever.

   1. The organism is widely distributed in the infected person and appears in the blood early in the disease process.

   2. After 10–14 days, the organisms appear in considerable numbers in the urine.

   3. Patients with Weil disease show striking antibody responses; serologic testing is useful for diagnosis of this disease.

4. Streptobacillus moniliformis and Spirillum minor are the species responsible for rat-bite fever. Although this condition occurs worldwide and is common in Japan and Asia, it is uncommon in North and South America and most European countries. Cases in the United States have been linked to bites or scratches by infected rodents (such as rats, mice, and gerbils). The case fatality rate is 7%–10% among untreated patients.