Laboratory Studies
- Peripheral blood smears
- Tick-borne relapsing fever (TBRF) is definitively confirmed in the laboratory with direct observation of spirochetes in peripheral blood smears during episodes of fever. A thin smear or thick drop of blood is deposited on a microscope slide, which is then stained with either Wright or Giemsa, and examined under oil immersion. On average, 5 organisms are visible per oil immersion field. See the image below.
Peripheral blood smear in relapsing fever. (Image originally printed in Blevins SM, Greenfield RA, Bronze MS. Blood smear analysis in babesiosis, ehrlichiosis, relapsing fever, malaria, and Chagas disease. Cleve Clin J Med. Jul 2008;75(7):521-30. Reprinted with permission from the Cleveland Clinic.) - Peripheral blood smears yield a sensitivity of 70%,[20] and the technique is more sensitive in TBRF than in louse-borne relapsing fever (LBRF).
- Smears performed between relapses do not demonstrate the organism and should be repeated when the fever reappears. Inexperience in reading smears or a low index of suspicion for the infection may also result in false-negative blood smear results.[2]
- Tick-borne relapsing fever (TBRF) is definitively confirmed in the laboratory with direct observation of spirochetes in peripheral blood smears during episodes of fever. A thin smear or thick drop of blood is deposited on a microscope slide, which is then stained with either Wright or Giemsa, and examined under oil immersion. On average, 5 organisms are visible per oil immersion field. See the image below.
- Direct or immunofluorescence staining: These techniques may also be used to visualize spirochetes using a fluorescence microscope.
- Dark-field microscopy: This may show spirochetes in the blood.
- Peripheral blood wet mounts: This may show red cells colliding with spirochetes.[2]
- Nonspecific laboratory findings: These include normal to mildly increased leukocyte counts, anemia, thrombocytopenia, increased liver enzyme levels, and prolonged coagulation parameters.
- Cerebrospinal fluid (CSF) studies: In patients with neurologic involvement, CSF studies show mononuclear pleocytosis and a mildly elevated protein level.[4]
Imaging Studies
- No special imaging is required in relapsing fever. Imaging would be performed only to evaluate suspected intracranial hemorrhage or other complications.
- Chest radiography may reveal pulmonary edema.
Other Tests
- Quantitative buffy coat is 100 times more sensitive than thick films in vitro and may be useful in diagnosis of relapsing fever. However, it requires special equipment.[21]
- The organism can be grown in culture using a specific liquid medium developed by Kelly.[22] In this technique, a couple of drops of blood are added to the medium, which is incubated at 30-37°C and kept for 2-6 weeks. Dark-field microscopy is used to periodically check for spirochetes.
- In the research setting, the patient’s blood can be inoculated into mice and the spirochetes amplified in murine blood.[5]
- Monoclonal antibodies can be used to diagnose B hermsii infection.[23]
- Serologies: Antibodies to Borrelia species can be detected with enzyme immunoassays. With this technique, TBRF is confirmed with (1) a 4-fold rise in titers between acute and convalescent samples or (2) a single reactive sample. However, few laboratories perform these assays, and the sensitivity needs to be improved. Enzyme-linked immunosorbent assay (ELISA) is most commonly performed using B hermsii as the antigen. False-positive ELISA results have been noted in patients infected with other Borrelia species. In addition, false-positive results for syphilis and Lyme disease have been described.[26, 27]
- An immunoreactive protein termed glycerophosphoryl diester phosphodiesterase (G1pQ) has been identified in spirochetes that cause relapsing fever. It recognizes antibodies produced during relapsing fever but, unlike serological testing, does not recognize the antibodies made in Lyme disease or syphilis.[2]
Histologic Findings
Spirochetes may be detected in tissue using silver stains (eg, Warthin-Starry or modified Dieterle). Alternatively, they may be visualized with immunofluorescence using antibodies.[6]
On gross pathology, endothelial cell edema, microvascular leakage, perivascular mononuclear infiltrates, microabscesses, and hemorrhage may be seen. In fatal LBRF, myocarditis with histiocytic infiltrates and microhemorrhages may be observed. In the liver and spleen, focal necrotic areas may be noted.[17]
Barbour AG, Hayes SF. Biology of Borrelia species. Microbiol Rev. Dec 1986;50(4):381-400. [Medline].
Dworkin MS, Schwan TG, Anderson DE Jr, Borchardt SM. Tick-borne relapsing fever. Infect Dis Clin North Am. Sep 2008;22(3):449-68, viii. [Medline].
Wynns HL. The epidemiology of relapsing fever. In: Moulton FR. A Symposium on Relapsing Fever in the Americas. American Association for the Advancement of Science. Washington, DC: 1942:100-5.
Blevins SM, Greenfield RA, Bronze MS. Blood smear analysis in babesiosis, ehrlichiosis, relapsing fever, malaria, and Chagas disease. Cleve Clin J Med. Jul 2008;75(7):521-30. [Medline].
Moursund WH. Historical introduction to the symposium on relapsing fever. In: Moulton FR. A Symposium on Relapsing Fever in the Americas. American Association for the Advancement of Science. Washington, DC: 1942:1-6.
Barbour AG. Microbiology, pathogenesis, and epidemiology of relapsing fever. UpToDate. Available at http://www.uptodate.com/online/content/topic.do?topicKey=tickflea/
11713&selectedTitle=2~15&source=search_result#references. Accessed November 25, 2008. Fuchs PC, Oyama AA. Neonatal relapsing fever due to transplacental transmission of Borrelia. JAMA. Apr 28 1969;208(4):690-2. [Medline].
Thein M, Bunikis I, Denker K, Larsson C, Cutler S, Drancourt M, et al. Oms38 is the first identified pore-forming protein in the outer membrane of relapsing fever spirochetes. J Bacteriol. Nov 2008;190(21):7035-42. [Medline].
Gelderblom H, Schmidt J, Londoño D, Bai Y, Quandt J, Hornung R, et al. Role of interleukin 10 during persistent infection with the relapsing fever Spirochete Borrelia turicatae. Am J Pathol. Jan 2007;170(1):251-62. [Medline].
Londoño D, Marques A, Hornung RL, Cadavid D. Relapsing fever borreliosis in interleukin-10-deficient mice. Infect Immun. Dec 2008;76(12):5508-13. [Medline].
Centers for Disease Control and Prevention (CDC). Acute respiratory distress syndrome in persons with tickborne relapsing fever--three states, 2004-2005. MMWR Morb Mortal Wkly Rep. Oct 19 2007;56(41):1073-6. [Medline].
Platonov AE, Karan LS, Kolyasnikova NM, Makhneva NA, Toporkova MG, Maleev VV, et al. Humans infected with relapsing fever spirochete Borrelia miyamotoi, Russia. Emerg Infect Dis. Oct 2011;17(10):1816-23. [Medline].
Brouqui P, Stein A, Dupont HT, Gallian P, Badiaga S, Rolain JM, et al. Ectoparasitism and vector-borne diseases in 930 homeless people from Marseilles. Medicine (Baltimore). Jan 2005;84(1):61-8. [Medline].
Barbour AG. Clinical features and management of relapsing fever. UpToDate. Available at http://www.uptodate.com/online/content/topic.do?topicKey=tickflea/
11413#1. Accessed November 25, 2008. Rhee KY, Johnson WD Jr. Borrelia species (relapsing fever). In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Vol 2. 6th ed. Philadelphia, PA: Churchill Livingstone; 2005:2795-8.
Goubau PF. Relapsing fevers. A review. Ann Soc Belg Med Trop. 1984;64(4):335-64. [Medline].
Southern PM, Sanford JP. Relapsing fever: a clinical and microbiological review. Medicine. 1969;48:129-49.
Perine PL, Parry EH, Vukotich D, Warrell DA, Bryceson AD. Bleeding in louse-borne relapsing fever. I. Clinical studies in 37 patients. Trans R Soc Trop Med Hyg. 1971;65(6):776-81. [Medline].
Dennis DT, Awoke S, Doberstyn EB, Fresh JW. Bleeding in louse-borne relapsing fever in Ethiopia; clinical and laboratory features in 29 patients. East Afr Med J. Apr 1976;53(4):220-5. [Medline].
Parola P, Raoult D. Ticks and tickborne bacterial diseases in humans: an emerging infectious threat. Clin Infect Dis. Mar 15 2001;32(6):897-928. [Medline].
van Dam AP, van Gool T, Wetsteyn JC. Tick-borne relapsing fever imported from West Africa: diagnosis by quantitative buffy coat analysis and in vitro culture of Borrelia crocidurae. J Clin Microbiol. Jun 1999;37(6):2027-30. [Medline].
Kelly R. Cultivation of Borrelia hermsi. Science. Jul 30 1971;173(995):443-4. [Medline].
Schwan TG, Gage KL, Karstens RH, Schrumpf ME, Hayes SF, Barbour AG. Identification of the tick-borne relapsing fever spirochete Borrelia hermsii by using a species-specific monoclonal antibody. J Clin Microbiol. Apr 1992;30(4):790-5. [Medline].
Fukunaga M, Okada K, Nakao M, Konishi T, Sato Y. Phylogenetic analysis of Borrelia species based on flagellin gene sequences and its application for molecular typing of Lyme disease borreliae. Int J Syst Bacteriol. Oct 1996;46(4):898-905. [Medline].
Jiang J, Temenak JJ, Richards AL. Real-time PCR duplex assay for Rickettsia prowazekii and Borrelia recurrentis. Ann N Y Acad Sci. Jun 2003;990:302-10. [Medline].
Magnarelli LA, Anderson JF, Johnson RC. Cross-reactivity in serological tests for Lyme disease and other spirochetal infections. J Infect Dis. Jul 1987;156(1):183-8. [Medline].
Magnarelli LA, Meegan JM, Anderson JF, Chappell WA. Comparison of an indirect fluorescent-antibody test with an enzyme-linked immunosorbent assay for serological studies of Lyme disease. J Clin Microbiol. Aug 1984;20(2):181-4. [Medline].
Guerrier G, Doherty T. Comparison of antibiotic regimens for treating louse-borne relapsing fever: a meta-analysis. Trans R Soc Trop Med Hyg. Sep 2011;105(9):483-90. [Medline].
[Best Evidence] Hasin T, Davidovitch N, Cohen R, Dagan T, Romem A, Orr N, et al. Postexposure treatment with doxycycline for the prevention of tick-borne relapsing fever. N Engl J Med. Jul 13 2006;355(2):148-55. [Medline].
Dworkin MS, Anderson DE Jr, Schwan TG. Tick-borne relapsing fever in the northwestern United States and southwestern Canada. Clin Infect Dis. Jan 1998;26(1):122-31. [Medline].
Scott R. Neurological complications of relapsing fever. Lancet. 1944;247:436-8.
Cadavid D, Barbour AG. Neuroborreliosis during relapsing fever: review of the clinical manifestations, pathology, and treatment of infections in humans and experimental animals. Clin Infect Dis. Jan 1998;26(1):151-64. [Medline].
Wengrower D, Knobler H, Gillis S, Chajek-Shaul T. Myocarditis in tick-borne relapsing fever. J Infect Dis. Jun 1984;149(6):1033. [Medline].

