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Tick-Borne Diseases, Relapsing Fever
Updated: Dec 9, 2008
Introduction
Background
Relapsing fever is an acute febrile illness caused by spirochetes of the genus Borrelia. The high fevers of presenting patients spontaneously abate and then recur. This characteristic pattern of remission and relapse not only gives relapsing fever its name but also allows it to be differentiated clinically from other febrile illnesses as it has since the 1840s.
Large outbreaks of louse-borne relapsing fever have occurred throughout the past century. These outbreaks usually occur following man-made breakdowns in public health, as typified by the epidemic following World War II that involved about 10 million people.
Pathophysiology
Relapsing fever is transmitted to humans by 2 vectors, ticks and lice. The human body louse, Pediculus humanus, is the specific vector (Pediculus pubis is not a vector). Louse-borne relapsing fever is more severe than the tick-borne variety.
Louse-borne relapsing fever is caused by Borrelia recurrentis. No animal reservoir exists. Lice that feed on infected humans acquire the Borrelia organisms that then multiply in the gut of the louse. When an infected louse feeds on an uninfected human, the organism gains access when the victim crushes the louse or scratches the area where the louse is feeding. B recurrentis infects the person via either abraded or intact skin (or mucous membranes) and then invades the bloodstream.
Soft ticks of the genus Ornithodoros spread the tick-borne variety. The responsible Borrelia species are identified closely with its tick vector and they share parallel nomenclature. (For example, Borrelia parkeri infects Ornithodoros parkeri; Borrelia hermsii is the agent transmitted by tick bite by Ornithodoros hermsii.) Soft ticks feed for short periods of time (an hour or so), and the Borrelia organisms are inoculated within minutes. This is an important distinction from other tick-borne diseases such as Lyme disease. Transplacental transmission has been reported.
Relapsing fever can be tick- or louse-borne. Soft-bodied ticks of the genus Ornithodoros transmit tick-borne cases. Below is an image of such a tick. Unlike the hard-bodied ticks, the Ornithodoros feed briefly and can transmit disease within minutes. Photo courtesy of Julie Rawlings, MPH, Texas Department of Health.
Regardless of the mode of transmission, a spirochetemia develops. Borrelia organisms then invade the endothelium. This can produce a low-grade disseminated intravascular coagulation and thrombocytopenia. The relapse phenomenon occurs because of genetically programmed shifting of outer surface proteins of the Borrelia that allows a new clone to avoid destruction by antibodies directed against the majority of the original infecting organisms. Thus, the person clinically improves until the new clone multiplies sufficiently to cause another relapse. Tick-borne disease tends to have more relapses (average of 3) compared with the louse-borne variety (often just 1).
The recent resurgence of interest in Borrelia because of Lyme disease and, especially the recent publication of the genomic sequence of B burgdorferi, has led to advances in the understanding of the host-parasite interactions of the relapsing fever Borrelia.
Frequency
United States
Louse-borne relapsing fever is not endemic in the United States, although an occasional traveler presents with an imported case.
Few cases of tick-borne relapsing fever are reported in the United States; however, sporadic cases continue to occur. It is highly focal, with 13 counties producing 50% of cases. Most of these are found in the late spring and summer in the western mountainous states, south into Texas, and northwest into Washington.
Undoubtedly, many cases occur that either are misdiagnosed or go unreported.
Clusters of cases are reported; often groups of campers share a rustic facility infested with rodents on which the ticks feed.
International
Endemic foci of louse-borne relapsing fever occur in much of the world where war, poverty, and overcrowding exist; all of which are conditions that favor louse infestation. Civil wars, which result in large refugee camps, are also fertile ground for lice and relapsing fever.
Mortality/Morbidity
- Mortality rates from 30-70% are reported in untreated patients during epidemics of the louse-borne variety; the mortality rate falls to about 5% with treatment. This striking figure probably reflects the underlying malnutrition and coexisting infections that exist in these situations.
- The mortality rate of patients with tick-borne relapsing fever who are treated is less than 1%.
Sex
A slight preponderance of female patients exists in louse-borne epidemics (60%); tick-borne relapsing fever occurs more often in males (60%) than in females. The latter figure probably reflects the greater likelihood of males being exposed to ticks through recreational and occupational activities.
Age
A trend toward pediatric cases of both forms of relapsing fever exists. In the case of the louse-borne variety, this may reflect the general state of health in populations where relapsing fever is endemic. Regarding the tick-borne disease, this may reflect activities that lead to tick exposure.
Clinical
History
Relapsing fever develops abruptly 3-18 days (average, 7-8 d) after exposure to the spirochete.
As with all the tick-borne diseases, the season of onset and epidemiologic history suggesting possible tick exposure are important clues. Ornithodoros ticks often frequent caves and decaying woodpiles. Many patients report a history of having spent time in rustic cabins in which the ticks gain access by hitching a ride on a rodent.
- Onset of symptoms generally is abrupt.
- Pulse is rapid in proportion to the fever, a point of differential value with typhoid fever with which louse-borne relapsing fever can be confused.
- Headache is a very common symptom, occurring in nearly 95% of cases.
- Myalgias and chills also occur in approximately 90% of cases.
- Arthralgias
- Weakness
- Anorexia
- Weight loss
- Cough
- Over the last several years, adult respiratory distress syndrome (ARDS) has been reported in several North American patients.
- Systemic symptoms
- Patients commonly complain of nausea, vomiting, and upper abdominal pain due to liver and spleen involvement.
- Hepatic and splenic involvement is more common in louse-borne relapsing fever.
- A dry cough frequently is observed, a feature that is in common with typhoid fever.
- Relapses
- The primary febrile episode typically ends after 3-6 days by crisis that can culminate in fatal shock. About 7-10 days later, the first relapse occurs abruptly. Subsequent relapses tend to be less severe.
- The primary febrile episode usually lasts an average of 3 days.1
- Louse-borne relapsing fever normally produces fewer relapses.
- In tick-borne disease, relapses average 3, and there can be more than 10.
Physical
Physical findings are not diagnostic.
- Fever (most common finding)
- Tachypnea
- Tachycardia
- Hypotension
- Abdominal tenderness with hepatosplenomegaly
- Petechial or maculopapular rash
- Rales
- Rhonchi
- Nuchal rigidity
- Lymphadenopathy
- Jaundice
- Iritis and iridocyclitis
- Neurologic findings are more common in louse-borne disease and include coma, cranial neuropathy (especially Bell palsy), hemiplegia, meningitis, and seizures.
Causes
Relapsing fever is caused by infection with the causative Borrelia species.
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References
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[Best Evidence] Hasin T, Davidovitch N, Cohen R, 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].
Fekade D, Knox K, Hussein K, et al. Prevention of Jarisch-Herxheimer reactions by treatment with antibodies against tumor necrosis factor alpha. N Engl J Med. Aug 1 1996;335(5):311-5. [Medline].
Anda P, Sanchez-Yebra W, del Mar Vitutia M, et al. A new Borrelia species isolated from patients with relapsing fever in Spain. Lancet. Jul 20 1996;348(9021):162-5. [Medline].
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].
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].
Dworkin MS, Anderson DE Jr, Schwan TG, et al. Tick-borne relapsing fever in the northwestern United States and southwestern Canada. Clin Infect Dis. Jan 1998;26(1):122-31. [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].
Horton JM, Blaser MJ. The spectrum of relapsing fever in the Rocky Mountains. Arch Intern Med. May 1985;145(5):871-5. [Medline].
Nordstrand A, Barbour AG, Bergstrom S. Borrelia pathogenesis research in the post-genomic and post-vaccine era. Curr Opin Microbiol. Feb 2000;3(1):86-92. [Medline].
Paul WS, Maupin G, Scott-Wright AO, et al. Outbreak of tick-borne relapsing fever at the north rim of the Grand Canyon: evidence for effectiveness of preventive measures. Am J Trop Med Hyg. Jan 2002;66(1):71-5. [Medline].
Raoult D, Roux V. The body louse as a vector of reemerging human diseases. Clin Infect Dis. Oct 1999;29(4):888-911. [Medline].
Further Reading
Keywords
tick-borne diseases, tick bite, relapsing fever, Borrelia, louse-borne relapsing fever, human body louse, Pediculus humanus, P humanus, Borrelia recurrentis, B recurrentis, lice, ticks, Ornithodoros, spirochetemia, Borrelia parkeri, B parkeri, Ornithodoros parkeri, O parkeri, Borrelia hermsii, B hermsii, Ornithodoros hermsii, O hermsii, soft tick
