The smear shows normochromic red blood cells and decreased platelets. More importantly, there is a spirochete in the right lower corner of the field with 12 loose coils consistent with Borrelia (5 to 12 loose coils). The most likely diagnosis based on the history and this smear is relapsing fever.


Relapsing fever is an infection caused by the spirochete Borrelia recurrentis, which is transmitted by ticks or lice that have fed on the blood of rodents. It is most common in the mountains of the western United States and tends to occur in epidemics.

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The most common symptoms in relapsing fever include fever, chills, headache, abdominal pain, vomiting, and arthralgia. Diarrhea is not a typical symptom. Physical examination in relapsing fever may be normal or may reveal an enlarged and/or tender liver and/or enlarged spleen. A rash may occur and may become petechial.

In relapsing fever, symptoms often relapse and recur multiple times, hence the name of the disease. Relapses typically occur every 1 to 2 weeks and can go on for months. Often the diagnosis is not made during the initial bout.

Laboratory data may show low platelets, low hemoglobin, and/or elevated liver enzymes. In addition, spirochetes may be visible if a smear is done. The white cell count is usually normal. Treatment for relapsing fever is doxycycline for 10 days. In allergic patients, a macrolide may be substituted. Similar to syphilis, another disease also caused by spirochetes, the rapid plasma reagin (RPR) may be positive and a Jarisch-Herxheimer reaction may occur soon after the initiation of treatment. See the chart for additional information on this condition.

Case Outcome

This patient was treated with doxycycline and did well.

Table 1. Relapsing Fever

Epidemiology Western US mountains. Borrelia recurrentis from rodent ticks or lice epidemics
Clinical Fever, chills, HA, abdominal pain, V, arthralgias >Hepatosplenomegaly, rash, CNS symptoms last 3-10 days then resolve but may recur every 1 to 2 weeks up to 3 to 10 times
Lab Spirochetes on complete blood count, high LFTs, low platelets, white blood cells usually normal, anemia. +RPR
Treatment Doxycycline, tetracycline hydrochloride, or erythromycin for 10 d. Aspirin for Jarisch-Herxheimer reaction


Brady Pregerson, MD, is an emergency physician at Cedars-Sinai Medical Center in Los Angeles and at Tri-City Medical Center in Oceanside, California.


  1. Pregerson B. Quick Essentials: Emergency Medicine: The One-Minute Consult—Version 4.0.; 2010.