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Borrelia burgdorferi (Lyme disease). Blood film. The genus Borrelia consists of spirochetal bacteria that cause relapsing fever and Lyme disease. The organisms can be found in the blood; and, the blood film
(along with antibody tests) is an important diagnostic modality

Tick-borne relapsing fever is characterized by recurring fevers separated by afebrile periods and is accompanied by nonspecific constitutional symptoms. It occurs after a patient has been bitten by a tick infected with a Borrelia spirochete. The diagnosis of tick-borne relapsing fever requires an accurate characterization of the fever and a thorough medical, social, and travel history of the patient. Findings on physical examination are variable; abdominal pain, vomiting, and altered sensorium are the most common symptoms. Laboratory confirmation of tick-borne relapsing fever is made by detection of spirochetes in thin or thick blood smears obtained during a febrile episode. Treatment with a tetracycline or macrolide antibiotic is effective, and antibiotic resistance is rare. Patients treated for tick-borne relapsing fever should be monitored closely for Jarisch-Herxheimer reactions. Fatalities from tick-borne relapsing fever are rare in treated patients, as are subsequent Jarisch-Herxheimer reactions. Persons in endemic regions should avoid rodent- and tick-infested areas and use insect repellents and protective clothing to prevent tick bites

Illustrative Case

A 60-year-old man presented to an emergency department in Boise, Idaho, with a one-month history of intermittent fevers and headaches. The initial fever peaked at 40.6°C (105°F), was accompanied by a headache, lasted for three days, and resolved spontaneously after an episode of shaking chills. The patient had a second fever 13 days later, peaking at 39.4°C (103°F) with diffuse abdominal pain and blurred vision. This fever lasted two days and resolved spontaneously. At the time of the second fever, a family physician assessed the patient. Routine blood tests were normal except an elevated total bilirubin level (6.0 mg per dL) [102.6 mmol per L]. An abdominal computed tomography scan was normal. The patient was referred to an ophthalmologist, who diagnosed iritis.

The patient developed a third fever with headache and visual symptoms 26 days after the initial symptoms, prompting presentation to the emergency department. Past medical history and family history were unremarkable. The patient took no medications. He reported traveling to Vietnam four years earlier and Honduras 18 months earlier, and he took malaria prophylaxis for both trips. The patient also had been camping in the Bear Valley region of Idaho. Review of systems was otherwise negative.

On examination, the patient was febrile (39.7°C [103.4°F]), tachycardic (113 beats per minute), and hypertensive (195/107 mm Hg). Other vital signs were stable, and physical examination was normal.

A complete blood count was normal. Manual differential demonstrated 81 percent segmented neutrophils and a low lymphocyte count (6 percent). Total bilirubin was elevated (2.3 mg per dL [39.33 mmol per L]; direct bilirubin, 0.4 mg per dL [6.84 mmol per L]). A reticulocyte count was elevated (3.37 percent). Urinalysis was positive for protein (1+). Scant spirochetes were detected in a peripheral blood smear prepared with Giemsa stain (Figure 1).
Figure 1

FIGURE 1. A spirochete (arrow) in a thin smear of peripheral blood with Giemsa stain.

A presumptive diagnosis of Borrelia infection was made, and the patient was admitted and started on tetracycline (500 mg orally, four times daily). The patient's maximum temperature in the hospital was 39.3°C (102.8°F), which returned to normal after 24 hours. Visual symptoms resolved after 24 hours, and he was discharged 36 hours after admission and continued tetracycline for 10 days. Further discussion with the patient revealed that the area where he had been camping had a large squirrel population, though he did not recall being bitten by any insects

Jarisch-Herxheimer Reaction

• The Jarisch-Herxheimer reaction occurs within 1 to 2 hours
of treatment of syphilis with antibiotics, especially penicillin
• The reaction is caused by release of pyrogen from the spirochetes
• It is most common during the treatment of secondary syphilis
(70%-90% of cases)
• The reaction is characterized by the following:
Fevers
Chills
Sweats
Headache
Hypotension
Worsening of the skin lesions
• The reaction usually resolves within 24 hours of treatment
• Treatment of the reaction is supportive only
• Similar reactions have been reported with treatment of the
following:
Lyme disease
Borreliosis
Brucellosis
Typhoid fever
Trichinellosis