Applied Evidence
Another risk to US travelers—malaria
To individualize preventive measures, rely on reported risk data for specific destinations, planned activities, and patient comorbidities.
THE CASE
A 76-year-old man with a history of coronary artery disease presented with a fever, headache, and malaise one week after returning from a big game hunting trip in South Africa. Five days after his return, he noticed lesions on his right leg that eventually scabbed over. He sought care at his local emergency department and with his primary care physician, and completed an empiric trial of azithromycin. His symptoms, however, persisted and he was referred to our institution for evaluation and treatment.
On exam, he had a temperature of 100.5° F, inguinal lymphadenopathy, and 2 eschars: a 1.5 cm one on his right groin and an identical one on the medial aspect of the right popliteal fossa (FIGURE 1).
THE DIAGNOSIS
Laboratory studies showed a white blood cell count of 3000/mcL, hemoglobin of 14.1 g/dL, and platelet count of 142,000/mcL; peripheral blood smear was normal. Blood and urine cultures showed no growth. A malaria smear and antibodies for Lyme disease, dengue fever, Chikungunya virus, and Q fever were also negative. A biopsy of the eschar demonstrated epidermal and dermal necrosis consistent with infectious vasculitis caused by rickettsial disease (FIGURE 2). A polymerase chain reaction (PCR) for the spotted fever group (R rickettsii, R akari, and R conorii) and typhus fever group of rickettsial agents (R typhi and R prowazekii) were negative. However, a PCR was positive for R africae, confirming the diagnosis of African tick-bite fever (ATBF).
DISCUSSION
Two common reasons patients returning from international travel seek medical attention are fever and rash.1 Initial assessment should include a detailed travel history of urban and rural exposures and any possible exposure to ticks or fleas. The time course of symptoms is important because some tropical infections can have long incubation periods.2
Rickettsial diseases are the most common febrile illness in patients returning from international travel.1 ATBF caused by R africae is the most common rickettsiosis among returning travelers1 and may be the most widespread of all spotted fever group rickettsiae that are known to be pathogenic to humans.3R africae is endemic to South Africa. The risk of contracting R africae is 4 to 5 times higher than the risk of contracting malaria in South Africa.1
R africae is transmitted through cattle and game ticks (Amblyomma species),1-7 and tends to cause mild illness with rare progression to complicated disease.3 The risk of infection is particularly high from November to April,7 and our patient had traveled during April.
Most patients with ATBF present with fever, headache, and malaise, and 50% develop a variable rash.1,2 Local lymphadenopathy often develops, and marked neck stiffness can occur.2 An eschar is present in 95% of cases.2 The finding of an eschar is often indicative of rickettsial infection; however, not all rickettsioses show eschars, and the absence of an eschar does not exclude rickettsial infection.1
ATBF is usually benign and self-limiting, and no fatalities have been reported.2,4,8 Complications such as peripheral nerve involvement, encephalitis, and myocarditis are rare.5,8 Since rickettsial diseases may be more severe in elderly patients with underlying diseases, empiric treatment with inpatient monitoring is justifiable.5
Don’t wait for lab confirmation to begin antibiotics
Laboratory findings in a patient with ATBF include pancytopenia, elevated serum C-reactive protein, and abnormal liver function tests.2,4 A blood PCR detects R africae,1,3 and if a rash or eschar is present, a biopsy can confirm the diagnosis.1 However, confirming the diagnosis is difficult if seroconversion has not occurred and PCR is not readily available.1 Also, antibodies may not be detected in patients who have a mild case of ATBF or those who are immunocompromised.5
If you suspect your patient has ATBF, don’t wait for laboratory confirmation; instead, initiate empiric treatment with doxycycline 100 mg bid twice daily for 5 to 7 days.1,2,4
Preventive measures include repellant lotions, clothing, and gear
Since there are no vaccines or prophylactic treatments for ATBF, counsel travelers on preventive measures.9 Instruct patients who plan to visit an endemic area such as sub-Saharan Africa or the West Indies to wear long-sleeved shirts, long pants, and hats. Individuals should also tuck their shirts into their pants and their pants into socks, as well as wear closed-toe shoes. When possible, it’s advisable to avoid woody and brushy areas.
Over-the-counter repellant lotions that contain ≥20% DEET are effective at preventing tick bites for several hours after an application, but should be reapplied as directed.9 These lotions should be applied after sunscreen. Advise patients that they can purchase clothing and gear that have been treated with the pesticide permethrin, or they can treat clothing and gear themselves. Explain, however, that permethrin should not be applied directly to skin.