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African Tick-Bite Fever Among International Travelers -- Oregon, 1998

In May 1998, the Oregon Health Division received a report from a local physician that nine persons developed annular skin lesions accompanied by influenza-like symptoms within 8 days of leaving southern Africa. All nine persons were members of a 34-person group from Oregon that traveled to Swaziland in April 1998 to participate in a 3-week humanitarian construction project. This report describes two cases of African tick-bite fever (ATBF) diagnosed in this group and underscores the importance of pretravel counseling about vectorborne illnesses and post-travel recognition of imported rickettsial diseases.

Case Reports

Case 1. A 61-year-old man developed an annular skin lesion 1.5 cm in diameter on his right lower leg 4 days after leaving the Swaziland construction site. The lesion had a dark center with an erythematous border. He also noted acute onset of fatigue, chills, and fever, but denied having other rashes or skin lesions. The patient was evaluated in Oregon by his physician, tickborne illness was diagnosed empirically and treated with 100 mg of doxycycline twice daily for 10 days. His systemic symptoms resolved completely within 24 hours of onset; however, full resolution of his skin lesion required more than 2 months. A serum sample obtained 6 days after symptom onset revealed antibodies reactive with Rickettsia rickettsii (the organism that causes Rocky Mountain spotted fever) at a titer of less than 1:8. A convalescent antibody titer obtained 4 weeks after symptom onset was 1:256. During his 3-week stay in Swaziland, the patient worked indoors and outdoors at two construction sites. He did not use insect repellent and did not notice or remove ticks from his body.

Case 2. A 56-year-old woman developed two erythematous annular skin lesions with dark centers 8 days after leaving the Swaziland construction site. The lesions were 1-2 cm in diameter and were on her back and right side. She also noted acute onset of fever, fatigue, chills, sweats, headache, myalgia, and arthralgias. She denied having other rashes or skin lesions. The patient was evaluated in Oregon by her physician, who noted a diffuse lymphadenopathy. Serologic titers for antibodies to rickettsial organisms were not obtained. She was empirically treated with 100 mg of minocycline twice daily for 10 days. Her systemic symptoms resolved 4 days after onset, but complete resolution of her skin lesions required more than 2 months. The patient worked indoors at the construction site. She did not use insect repellent and reported no tick bites or tick removals during her stay.

Summary of Cases

Eight of the nine reported ill persons were available for interview. Median age was 54 years (range: 41-65 years); five were male. All eight case-patients interviewed reported developing one or more annular skin lesions, 0.5-3.0 cm in diameter, characterized by dark centers and erythematous borders within 8 days of leaving southern Africa. Six developed skin lesions accompanied by fatigue, chills, and fever. Rash, other than the annular lesions, was uniformly absent. Median symptom duration was 4 days (range: 1-15 days), and no patient required hospitalization. Six had pretravel contact with a health-care provider, but none recalled counseling about tickborne diseases endemic to southern Africa. No ill person recalled a tick bite or tick removal during their stay, and none reported consistent use of insect repellent. Ill persons sought medical attention after returning to the United States, and all were treated with antimicrobial medications. Case-patient 1 had serologic results consistent with acute rickettsial infection. For another case-patient, acute and convalescent (collected after he completed treatment with doxycycline) serologies did not reveal elevated levels of antibody reactive with R. rickettsii.

Reported by: S Neal, MD, Albany; P Cieslak, MD, K Hedberg, MD, D Fleming, MD, State Epidemiologist, Dept of Human Resources, Oregon Health Div. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Div of Applied Public Health Training, Epidemiology Program Office; and an EIS Officer, CDC.

Editorial Note

Editorial Note: During 1986-1996, * the number of U.S. residents traveling to Africa increased by 70% (1). An estimated 19 million U.S. residents traveled overseas in 1996, including approximately 455,000 persons who traveled to Africa (1). In Africa, diseases for which travelers are at risk include vectorborne illnesses (e.g., ATBF and boutonneuse fever {BF}). ATBF, caused by R. africae, is transmitted by an infected Amblyomma tick and is endemic in sub-Saharan Africa (2,3). BF, caused by R. conorii, is transmitted by an infected Rhipicephalus tick and is endemic throughout Africa, the Middle East, and southern Europe (3-5). Tache noire, the annular skin lesion with a dark center and erythematous border, is common in both ATBF and BF, but diffuse rash is more common in BF and rare in ATBF (2,4). Although not definitive, the uniform absence of diffuse rash in case-patients is more consistent with ATBF than with BF.

ATBF and BF have been recognized as distinct clinical entities for many years, and differentiation of the etiologic agents (R. africae and R. conorii) has been possible since 1994 (3). Human antibodies cross-react to various rickettsial antigens, including R. africae, R. conorii, and R. rickettsii; therefore, serologic tests for rickettsial disease are group-specific but not species-specific (6). In the United States, patient serum is generally evaluated for antibodies reactive with R. rickettsii antigens, and final diagnosis is made by correlating serologic results with a patient's clinical and epidemiologic history.

The distinctive skin lesions, clinical symptoms, travel histories, and serology results indicate that the illnesses described in this report were caused by a tickborne rickettsial organism endemic in southern Africa. Among case-patients in this report, serologic results in one patient were consistent with acute rickettsial infection. The travel history effectively eliminates R. rickettsii as a causative agent but differentiation between R. africae and R. conorii is less clear.

The findings in this report underscore the importance of vectorborne illness as a topic of pretravel health-care counseling and post-travel diagnosis. To minimize the risk for BF, ATBF, and other tickborne diseases, clinicians should obtain a trip itinerary from patients traveling overseas and, when appropriate, provide advice about tick-bite prevention. Regular tick checks, prompt removal of any ticks, and regular use of insect repellents should be advised for all persons traveling to areas where R. africae and R. conorii are endemic. Travelers returning with tache noire skin lesions, fever, and influenza-like symptoms from areas where these illnesses are endemic should be evaluated for tickborne rickettsial diseases. Laboratory diagnosis can be made by measuring acute and convalescent serum antibodies to R. rickettsii or by immuno-fluorescent detection of the organism in biopsies taken from tache noire lesions (7). Doxycycline for a minimum of 7 days is the treatment of choice; however, chloramphenicol or a fluroquinalone are accepted antimicrobial alternatives (8).

Additional information about general and disease-specific health recommendations for international travel is available from CDC's "Yellow Book" (9) and World-Wide Web site


  1. US Department of Commerce. ITA: tourism industries. World-Wide Web site Accessed July 14, 1998.

  2. Brouqui P, Harle JR, Delmont J, Frances C, Weiller PJ, Raoult D. African tick-bite fever: an imported spotless rickettsiosis. Arch Intern Med 1997;157:119-24.

  3. Kelly PJ, Beati L, Matthewman LA, Mason PR, Dasch GA, Raoult D. A new pathogenic spotted fever group rickettsia from Africa. J Trop Med Hyg 1994;97:129-37.

  4. McDonald JC, MacLean JD, McDade JE. Imported rickettsial disease: clinical and epidemiologic features. Am J Med 1988;85:799-805.

  5. Dupont HT, Brouqui P, Faugere B, Raoult D. Prevalence of antibodies to Coxiella burnetti, Rickettsia conorii, and Rickettsia typhi in seven African countries. Clin Infect Dis 1995;21:1126-33.

  6. Hechemy KE, Raoult D, Fox J, Han Y, Elliott LB, Rawlings J. Cross-reaction of immune sera from patients with rickettsial diseases. J Med Microbiol 1989;29:199-202.

  7. Raoult D, deMicco C, Gallais H, Toga M. Laboratory diagnosis of Mediterranean spotted fever by immunofluorescent demonstration of Rickettsia conorii in cutaneous lesions. J Infect Dis 1984;150:145-8.

  8. Walker DH, Raoult D. Rickettsia rickettsii and other spotted fever group rickettsia (Rocky Mountain Spotted Fever and other spotted fevers). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practices of infectious diseases. 4th ed. New York, New York: Churchill Livingstone, 1995:1721-6.

  9. CDC. Health information for the international traveler 1996-97. Atlanta, Georgia: US Department of Health and Human Services, CDC, 1997.

Data collected on outbound U.S. residents spending greater than or equal to 1 nights in an overseas country. These data exclude visits to Canada and Mexico.

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