Tick-borne disease

Author: Robert L. Bratton, G. Ralph Corey
Date: June 15, 2005

Tick-borne diseases in the United States include Rocky Mountain spotted fever, Lyme disease, ehrlichiosis, tularemia, babesiosis, Colorado tick fever, and relapsing fever. It is important for family physicians to consider these illnesses when patients present with influenza-like symptoms. A petechial rash initially affecting the palms and soles of the feet is associated with Rocky Mountain spotted fever, whereas erythema migrans (annular macule with central clearing) is associated with Lyme disease. Various other rashes or skin lesions accompanied by fever and influenza-like illness also may signal the presence of a tick-borne disease. Early, accurate diagnosis allows treatment that may help prevent significant morbidity and possible mortality. Because 24 to 48 hours of attachment to the host are required for infection to occur, early removal can help prevent disease. Treatment with doxycycline or tetracycline is indicated for Rocky Mountain spotted fever, Lyme disease, ehrlichiosis, and relapsing fever. In patients with clinical findings suggestive of tick-borne disease, treatment should not be delayed for laboratory confirmation. If no symptoms follow exposure to tick bites, empiric treatment is not indicated. The same tick may harbor different infectious pathogens and transmit several with one bite. Advising patients about prevention of tick bites, especially in the summer months, may help prevent exposure to dangerous vector-borne diseases.

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Because for family people continue to interact with nature, patients will continue to present to physician offices with tick-borne diseases. It is important physicians to recognize these ill-nesses because early, accurate diagnosis may lessen the morbidity and mortality of these treatable diseases. This article provides an update on the more common tick-borne diseases. Agents and characteristics of tick-borne disease are summarized in Tables 1 and 2. (1)

Rocky Mountain Spotted Fever

EPIDEMIOLOGY

Rocky Mountain spotted fever is caused by Rickettsia rickettsii and is the most common rickettsial disease in the United States. (2) The disease is limited to the Western hemisphere and occurs in all states except Maine, Hawaii, and Alaska. The disease is more common in the coastal Atlantic states from April to September, although infections may occur year-round further south. (3) The wood tick (Dermacentor andersoni) is the principal vector in the western United States, whereas the dog tick (Dermacentor variabilis) is the most common vector in the eastern and southern United States. Transmission from person to person is not thought to occur. The incidence of Rocky Mountain spotted fever is highest in children five to nine years of age. (4)

SIGNS AND SYMPTOMS

Typically in tick-borne diseases, a tick bite is recalled by 50 to 70 percent of patients. (3,4) The onset of symptoms of Rocky Mountain spotted fever usually begins five to seven days after inoculation. Common symptoms include generalized malaise, myalgias (especially in the back and leg muscles), fever, frontal headaches, nausea, and vomiting. Other symptoms may include nonproductive cough, sore throat, pleuritic chest pain, and abdominal pain. The classic presenting symptoms include sudden onset of head-ache, fever, and chills accompanied by an exanthem appearing within the first few days of symptoms. Initially, lesions appear on the palms, soles, wrists, ankles, and forearms. The lesions are pink and macular and fade with applied pressure. The rash then extends to the axilla, buttocks, trunk, neck, and face, becoming maculopapular and then petechial (Figure 1 (5)). The lesions may then coalesce to form large areas of ecchymosis and ulceration. Respiratory and circulatory failure, as well as neurologic compromise, may occur. (6) Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at especially high risk for complications and poor outcomes. (7)

[FIGURE 1 OMITTED]

DIAGNOSIS

The diagnosis of Rocky Mountain spotted fever is based primarily on clinical signs and symptoms. If a rash is present, the use of skin biopsy and immunofluorescent staining for Rickettsia is highly specific, although with only slightly more than 60 percent sensitivity. Laboratory testing is of limited usefulness but may include thrombocytopenia and hyponatremia. (8) Elevation of specific enzyme-linked immunosorbent assay (ELISA) and latex agglutination titers usually is delayed until the convalescence period.

TREATMENT

Fever and headache during peak months of tick exposure in endemic areas should suggest Rocky Mountain spotted fever. Rash, thrombocytopenia, and hyponatremia make immediate treatment imperative. Antimicrobial agents for the treatment of Rocky Mountain spotted fever include tetracycline, doxycycline (Vibramycin), and chlor-amphenicol (Chloromycetin) for a minimum of seven days. (9) Fluoroquinolones also may be effective, but are not recommended for routine use in patients with Rocky Mountain spotted fever because of a lack of evidence. (10) For optimal effect, it is critical to treat patients early in the course of their illness. According to the Centers for Disease Control and Prevention, appropriate antibiotic treatment should be initiated immediately when there is a suspicion of Rocky Mountain spotted fever on the basis of clinical and epidemiologic findings. Treatment should not be delayed until laboratory confirmation is obtained. (7)

Lyme Disease

EPIDEMIOLOGY

Lyme disease is the most common vector-borne infectious disease in the United States. (9) The disease is caused by the spirochete Borrelia burgdorferi. In the United States, the main vector is Ixodes scapularis (Figure 2 (11)), commonly referred to as the black-legged or deer tick because the female tick often attaches itself to the white-tailed deer during the winter. Natural reservoirs for B. burgdorferi include the white-footed mouse and other small mammals. The larvae or nymphs of the tick feed on the white-footed mouse and become infected. Adult ticks or, more commonly, nymphs may then infect humans. Studies using animals have shown that infected nymphal-stage ticks must remain attached for 36 to 48 hours or longer, and infected adult ticks must remain attached for 48 to 72 hours or longer, before the risk of transmission of B. burgdorferi becomes substantial. (12-15) There is no evidence that Lyme disease can be transmitted by mosquitoes, flies, or fleas. Blood products have never been associated with transmission of Lyme disease. (16)

[FIGURE 2 OMITTED]

SIGNS AND SYMPTOMS

Lyme disease typically develops in three stages. Stage 1 (early localized) Lyme disease occurs seven to 10 days after tick bite. Findings include typical rash (erythema migrans) in 75 percent of patients at the site of the tick bite. The rash typically develops as an annular macule or papule with central clearing that may expand to a diameter of up to 50 cm. Other indications include influenza-like symptoms of low-grade fevers, fatigue, arthralgias, headaches, cough, and regional lymphadenopathy. Stage 2 (early disseminated) Lyme disease occurs a few weeks after the initial infection. Symptoms include multiple secondary cutaneous annular lesions, fever, adenopathy, and central nervous system symptoms. Cough and pharyngitis may occur. Stage 3 (late chronic disease) symptoms include chronic arthritis, central nervous system impairment, dermatitis, and keratitis. Other symptoms may include neurologic abnormalities such as meningoencephalitis, Bell's-like palsy, and radiculopathies, and myocardial abnormalities such as atrioventricular block, pericarditis, and cardiomegaly. (8)

DIAGNOSIS

Early diagnosis of Lyme disease in a patient with typical erythema migrans in an endemic area does not require laboratory confirmation. However, ELISA testing is 89 percent sensitive and 72 percent specific. Positive results on ELISA testing should be confirmed with Western blotting. Polymerase chain reaction testing, although not widely available, may be useful for the diagnosis, especially with fluid from the joints of the affected patient. (3) Isolation of B. burgdorferi from most tissues and body fluids by culture is difficult to achieve and requires weeks to grow before it can be analyzed.

TREATMENT

REFERENCES

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ROBERT L. BRATTON, M.D., is a consultant in the Department of Family Medicine at the Mayo Clinic, Scottsdale, Ariz., and associate professor of family medicine at the Mayo Medical School, Rochester, Minn. He received his medical degree from the University of Kentucky, Lexington, and completed a residency in family medicine at the Mayo Clinic, Rochester, Minn.

G. RALPH COREY, M.D., is professor of medicine and infectious diseases at Duke University Medical Center, Durham, N.C. He received his medical degree at Baylor University, Waco, Tex., and completed his internship, residency, and chief residency in internal medicine, and an infectious disease fellowship at Duke University Medical Center.

Address correspondence to Robert L. Bratton, M.D., Mayo Clinic Family Medicine--Thunderbird, 13737 N. 92nd St., Scottsdale, AZ 85260. Reprints are not available from the authors.

The authors indicate that they do not have any conflicts of interest. Sources of funding: none reported.

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