Relapsing fever typically refers to malaria-like illnesses caused by various Borrelia species, characterized by recurrent fevers, chills, and malaise. The causative organism and associated vector vary based on the geographic area of exposure.
The term relapsing fever refers to a variety of recurrent fever syndromes caused by the spirochete, Borrelia. Borrelia recurrentis is the cause of epidemic relapsing fever, which is reported most frequently in northern and eastern Africa. Tick-borne relapsing fever is reported the United States and can be caused by several species, including Borrelia hermsii, Borrelia turicatae, and Borrelia parkeri.
Borrelia recurrentis, or epidemic relapsing fever, is reported most commonly in areas of crowding and poor personal hygiene. It is transmitted via lice and has decreased in frequency substantially since the first half of the 20th century. However, it is still commonly reported in parts of Africa. Other species causing relapsing fever in Africa include Borrelia duttonii, Borrelia hispanica, and Borrelia crocidurae. Humans are the only known host and reservoir of Borrelia recurrentis. In contrast, small rodents and other mammals may serve as a reservoir for tick-borne Borrelia species. Borrelia hermsii, or tick-borne relapsing fever, is reported in the United States in Colorado, near Lake Tahoe, and near the Grand Canyon. It is transmitted via the bite of soft bodied, night feeding Ornithodoros ticks. Other species that cause tick-borne relapsing fever in the United States include Borrelia turicatae and Borrelia parkeri, also transmitted via tick bite. As the ticks feed at night, patients are often unaware of the bite. Borrelia miyamotoi is a relapsing fever, similar to Lyme disease, transmitted by the Ixodes tick. It is reported in the northeastern United States, Japan, and Russia, with slight variations in presentation depending on geography.
Relapsing fever is caused by Borrelia species, which are fastidious spirochetes. These spirochetes are large with irregular spirals and readily stain with aniline dyes. Although Borrelia is technically gram-negative, they are most readily identified by Giemsa or Wright staining. Borrelia recurrentis infection typically occurs after the bite of an infected louse. However, the infection may also occur through intact skin and mucosal surfaces. Borrelia hermsii, Borrelia parkeri and Borrelia turicatae are transmitted via the bite of soft bodied Ornithodoros ticks rather than through intact skin or mucosa. Borrelia miyamotoi is transmitted via the Ixodes tick, similar to Lyme disease. The clinical manifestations of relapsing fever, including fever, myalgias, chills, and arthralgias, are caused by an endotoxin-like substance produced by the spirochete. The initial febrile episode in relapsing fever resolves due to the development of antibodies directed at surface proteins of the organism. However, a reservoir of organisms in reticuloendothelial organs undergo genetic reassortment to alter the expression of surface proteins. This allows for escape from immune clearance and re-emergence of spirochetemia and clinical symptoms. The typical recurrence pattern of Borrelia symptoms in relapsing fever is due to repeated cycles of reassortment of surface proteins followed by antibody-mediated suppression of infection. Both the Borrelia organism and the saliva of the infected tick are thought Infection is not associated with long-term immunity and patients may be reinfected as soon as six months after initial infection.
The incubation period is typically four to 18 days following exposure to Borrelia. The symptoms of relapsing fevers are characterized by the abrupt onset of fever and chills, often accompanied by malaise, arthralgias, and myalgias. Hemorrhagic and non-hemorrhagic rashes, nausea, vomiting, jaundice, and neurologic abnormalities may also occur. After resolution of the first episode, which typically lasts one week, patients will experience several recurrences of fever that are shorter and less severe. Episodes occur every five to ten days and may persist for several cycles before resolution. In an epidemic, or louse-borne, relapsing fever, there are typically only one or two episodes of fever. However, in endemic, tick-borne relapsing fever, three to seven recurrences may occur before resolution of symptoms.
Diagnosis of relapsing fever requires a careful history with attention to travel history and other geographic information, living conditions and the temporal pattern of the symptoms. Laboratory evaluation may include leukopenia or leukocytosis, as well as thrombocytopenia. Diagnosis is confirmed by detection of Borrelia in Giemsa-stained blood films, serologic analysis or via PCR detection of the organism. These organisms are not identifiable on routine laboratory cultures. Diagnostic yield is highest with the earlier febrile episodes and decreases with each recurrence. Early in the course of illness, the number of spirochetes visible in the blood can reach 100,000/mm3. Between episodes and in later recurrences, the spirochetes may not be visible at all. Serology may also be used to diagnose tick-borne relapsing fever, particularly in situations in which diagnosis is suspected later in the course of illness. In that case, repeated testing with a rise in Immunoglobulin G (IgG) is suggestive of recent infection. However, these serologic tests cross react with other spirochetes such as Leptospirosis and syphilis and must be interpreted in the setting of clinical symptoms.
Relapsing fever is treated with doxycycline for seven to ten days. In children under eight years of age, penicillin or erythromycin are the preferred agents due to the concern of dental staining with doxycycline use. With antibiotic treatment, mortality of epidemic relapsing fever decreases from 10% to 40% to 2% to 4%. Fatalities are rare in tick-borne relapsing fever. In both cases, mortality is attributed to myocarditis. It is important to observe patients for several hours after initiation of antibiotic therapy, as Jarisch-Herxheimer reaction is common. Jarisch-Herxheimer reaction is a sepsis-like response to the release of inflammatory contents from within the bacteria after lysis by antibiotics. It is rarely fatal and managed with supportive care. This reaction is more common in adolescents than in younger children. Borrelia infections may also be self-limited and resolve without treatment in some cases.
There is currently no vaccine available for any of the Borrelia species associated with relapsing fever. Avoidance of louse and tick exposure through hygiene, environmental cleaning to remove rodent nesting material and insect repellant can decrease the risk of infection. As transmission is typically vector-borne, standard precautions are recommended, but other isolation is not required other than eradication of body lice.