Case Based Pediatrics For Medical Students and Residents
Department of Pediatrics, University of Hawaii John A. Burns School of Medicine
Chapter VI.26. Rocky Mountain Spotted Fever
Douglas K. Kwock, MD
July 2002

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This is a 12 year old male who presented to the office 2 days ago with a 2 day history of fever, headaches, malaise, and generalized myalgias. He was diagnosed with a "viral syndrome" and given instructions for home symptomatic care. He is now in the emergency department with a rash that started on his hands and feet, spreading up his arms and legs. The fever, headaches, and myalgias have persisted. Mother states that today her son seems "out of it ".

Exam: VS T 40.2 C, P 100, R 26, BP 115/70. He is laying in a hospital gurney, awake and responsive, but tired and ill appearing. His skin has a maculopapular rash that blanches under pressure on the upper and lower extremities, including his palms and soles, and a few scattered macular lesions located on the upper trunk and back. There is a small 3mm round healed scab lesion on the left calf. His head is atraumatic and nontender. He has no mucosal (eye, nose, mouth, and throat) lesions. He does not exhibit any meningeal signs. His heart, lung, and abdominal exams are normal. There is tenderness to gentle palpation of his thigh and calf muscles. He is oriented and responds appropriately.

Laboratory studies reveal a normal white blood cell count that is slightly left shifted. He has a platelet count of 105,000. His serum sodium is 132mEq/L. Cerebrospinal fluid is normal.

The patient is asked about the scab on his calf. Four days prior to the onset of illness, while deer hunting with friends, he noticed an engorged tick on his calf. The tick was removed by "squeezing and scratching" causing a small abrasion that he soon forgot about. He is started in doxycycline. Rocky mountain spotted fever serologies are ordered on his blood.


Rocky mountain spotted fever (RMSF) is a tick-borne disease caused by the gram-negative intracellular bacterium Rickettsia rickettsii. It is the second most common tick transmitted disease in the United States. Among the rickettsial illnesses, it is the most common and severe in the United States (1).

The disease was first recognized in Idaho and Montana in the late 1800s and initially thought to be limited to the Rocky Mountain region. Today RMSF is seen in all geographic areas of the continental United States. Over half of reported cases are concentrated in the south-Atlantic and south-central regions. The highest rates of disease are reported in North Carolina and Oklahoma (2). Though historically significant, the "Rocky Mountain" moniker is misleading relative to the current disease epidemiology.

Males have a higher incidence of disease than females. RMSF is of pediatric concern because children <15 years of age account for the majority of infections with the highest incidence in children age 5 to 9 years (2).

The wood tick (Dermacentor andersoni) found in the Western and Rocky Mountain States and the dog tick (Dermacentor variabilis) found east of the Rocky Mountains are the primary hosts and vectors of R. rickettsii. Infected female ticks can transmit infection transovarially and lay infected eggs, perpetuating infection from generation to generation. Ticks can acquire the infection while feeding on an infected rickettsemic host. Tick nymph and larva stages primarily feed on small mammals. Adult ticks feed on large domestic mammals, including humans. Once a tick becomes infected, it will maintain the infection for life even across molting stages.

Cases can occur throughout the year but the majority (90%) occur during April through September (2). This seasonality correlates with periods of heightened outdoor human activity, and increased tick feeding activity amplifying the likelihood of exposure. Ticks transmit infection during a blood meal. Transmission usually occurs after the tick has been attached for a minimum of 6 to 10 hours. A history of tick bite or exposure to tick infested areas is often not recalled on initial evaluation and is obtained in only 60% of RMSF cases.

Prior to the advent of effective therapy, 30% of RMSF cases were fatal. Currently, the mortality rate is 2 to 4% despite available appropriate treatment (1). Poor outcome is usually the result of delayed diagnosis and the subsequent delay in initiating appropriate antimicrobial therapy (3).

The average incubation period of RMSF is 5 to 7 days (range 2 to 14 days). Early signs and symptoms of RMSF are nonspecific. Prominent features of RMSF are fever, headaches, myalgias, and malaise. The onset of fever is usually abrupt. Headaches in older patients are intense, persistent, and refractory to relief efforts. Gastrointestinal complaints (nausea, vomiting, abdominal pain) are common.

The most characteristic feature of RMSF is a rash that develops on days 2 to 4 of illness. It appears as a discrete macular or maculopapular rash that blanches with pressure. The ankles and wrists are initially involved. Rash on the palms and soles is characteristic of RMSF. The rash spreads proximally up the arms and legs and eventually involves the trunk. Petechial and hemorrhagic lesions develop giving the classic "spotted" appearance of the illness. However, there have been reports of "spotless" or "almost spotless" RMSF illnesses. During convalescence, desquamation may occur in the most affected skin areas.

Fever, rash, and a history of tick bite comprise the "classic triad" of RMSF. This triad is seen in two-thirds of patients. Because the rash typically appears late in the course of illness, the classic triad is rarely useful in assisting with an early diagnosis which is critical to successful management.

Central nervous system involvement may develop in severe RMSF with symptoms of disorientation, meningismus, seizures, and coma. Cardiac complications include arrhythmias and congestive heart failure. Other less frequent signs and symptoms are pneumonitis, hepatosplenomegaly, edema, and conjunctivitis (4).

The initial presentation of RMSF is nonspecific and can mimic any generalized febrile illness. The maculopapular rash of measles and non-polio enteroviruses can resemble the rash of RMSF. A petechial rash necessitates the consideration of meningococcemia or septic shock (staphylococcus or streptococcus). Ehrlichiosis shares many similar features with RMSF.

There is no laboratory test that definitively diagnoses RMSF in the early phase of illness. Thus, an early diagnosis depends on a high index of suspicion, a compelling clinical presentation, and suggestive ancillary laboratory data.

The CBC WBC may be high, normal, or low but is usually left shifted. Thrombocytopenia is common in RMSF. Mild thrombocytopenia is probably related to platelet adherence to affected endothelial cells. Severe thrombocytopenia usually represents a consumptive coagulopathy. Hyponatremia is common. CSF is usually normal but may demonstrate a mild pleocytosis.

Diagnosis is made by serologic studies. The most sensitive and specific tests are indirect immunofluorescent antibody (IFA), enzyme immunoassay (EIA), and compliment fixation (CF). Other available serologic studies are latex agglutination (LA), indirect hemagglutination (IHA), and microagglutination (MA). Antibodies can be detected 7 to 10 days from disease onset. A single serum IFA titer of 1:64, CF titer of 1:16, or LA, IHA, or MA titer of 1:128, are highly suggestive of RMSF. A 4-fold rise between acute and convalescent antibody titers is diagnostic (5).

Early treatment is necessary and often empiric based on index of suspicion considering history, clinical course, and epidemiology. Treatment should not be withheld until a definitive diagnosis is made. Delay in initiating treatment leads to a poorer prognosis. Without treatment, RMSF can be fatal. Chloramphenicol, tetracycline, and doxycycline are effective against R. rickettsii. Doxycycline is the drug of choice for treatment of RMSF in patients of any age. Historically, chloramphenicol was recommended for children <8 years of age. Tetracycline and doxycycline were not favored because they bind to calcium of developing teeth and bones causing permanent discoloration. However, there are several reasons why doxycycline is the recommended first-line therapy. It does not bind to calcium as readily as tetracycline. A single course of doxycycline treatment carries little risk of teeth staining. Chloramphenicol has been associated with the development of irreversible aplastic anemia, and has been shown to be less effective than doxycycline for treatment of RMSF (2). Doxycycline is also active against ehrlichiosis, which may be clinically indistinguishable from RMSF. The efficacy of chloramphenicol in ehrlichiosis has not been established. Doxycycline is given at a dose of 2 to 4 mg/kg/day, divided every 12 hours, with a maximum dose of 200mg/day. The dose is the same regardless of oral or intravenous administration. Duration of therapy is for a minimum of 5 to 7 days and until the patient has been afebrile for at least 48 hours (5).

Limiting exposure to ticks is the most effective method of decreasing the risk of disease. If tick exposure is anticipated, there are several suggested means of protection. Clothing should cover a maximal amount of surface area to minimize exposed skin and should be light-colored allowing easy tick detection. Long pants should be tucked into socks or boots. Tick or insect repellants should be applied to clothing and exposed skin. Thorough body checks should be performed after exposure to a tick infested area. Particular attention should be paid to the head and scalp where ticks may be difficult to find. Proper skin removal of ticks is important in decreasing the risk of infection. Squeezing, crushing, pinching, or the folk remedy of burning the tick with a cigarette may actually facilitate rickettsiae transmission. The tick should be removed with a fine-tipped tweezer grasped as close to the skin as possible and pulled upward with a slow steady pressure. The skin site should be cleaned and disinfected. If possible, the tick should be saved for identification if illness develops.

There is no licensed vaccination for prevention of RMSF. Prophylactic therapy for asymptomatic individuals with a recent tick bite or exposure to a tick infested area is not recommended.

Full recovery is the rule with administration of appropriate antibiotics within 5 days of disease onset. Fulminant fatal RMSF has been associated with glucose-6-phosphate dehydrogenase (G6PD) deficiency (6), possibly related to increased hemolysis due to infection.


Questions

1. True/False: RMSF is most prevalent in the Rocky Mountain states.

2. True/False: RMSF can be "ruled out" based on a lack of history of tick bite.

3. True/False: Treatment of RMSF is often empiric.

4. True/False: Rash typically starts on the trunk and spreads distally.

5. Which is the preferred method of removing an attached tick?
. . . . . a. Use a lit match or cigarette to burn the tick stimulating it to detach and flee.
. . . . . b. Gently pinch the body of the tick with fingers and lift straight off.
. . . . . c. Use fine-tipped tweezers to grasp the tick as close to the skin as possible and pull upward with slow steady pressure.
. . . . . d. Apply petroleum jelly (Vaseline) over the tick and wait for the tick to suffocate or detach for air.
. . . . . e. Don't remove, leave the tick alone.

6. Which of the following is NOT a recommended means of RMSF prevention?
. . . . . a. Insect or tick repellants to clothing and exposed skin.
. . . . . b. Prophylactic doxycycline prior to exposure to tick infested areas.
. . . . . c. Minimize exposed skin with light [Note spelling change]-colored clothing.
. . . . . d. Avoid known tick infested areas.
. . . . . e. Survey skin and scalp after exposure to tick infested areas.


References

1. Edwards MS, Feigin RD. Chapter 194 - Rickettsial Diseases. In: Feigin RD, Cherry JD (eds). Textbook of Pediatric Infectious Diseases, fourth edition. 1998, Philadelphia: WB Saunders, pp. 2239-2245.

2. Dalton MJ, Clarke MJ, Holman RC, et al. National surveillance for Rocky Mountain spotted fever, 1981--1992: epidemiologic summary and evaluation of risk factors for fatal outcome. Am J Trop Med Hyg 1995;52:405-413.

3. Centers for Disease Control and Prevention. Consequences of Delayed Diagnosis of Rocky Mountain Spotted Fever in Children - West Virginia, Michigan, Tennessee, and Oklahoma, May-July 2000. MMWR 2000;49(39):885-888.

4. Thormer AR, Walker DH, Petri WA. Rocky Mountain Spotted Fever. Clin Infect Dis 1998;27:1353-1360.

5. American Academy of Pediatrics. Rocky Mountain Spotted Fever. In: Pickering LK, et al (eds). 2000 Red Book: Report of the Committee on Infectious Diseases, 25th ed. 2000, Elk Grove Village, IL: American Academy of Pediatrics, pp. 491-493.

6. Walker DH, Hawkins HK, Hudson P. Fulminant Rocky Mountain spotted fever . Its pathologic characteristics associated with glucose-6-phospate dehydrogenase deficiency. Arch Pathol Lab Med 1983;107:121-125.


Answers to questions

1. False. Primarily south-Atlantic and south-central states.

2. False. A history of tick bite or exposure is obtained in only 60% of cases.

3. True. Therapy should never be withheld until a definitive diagnosis is made. Poorer outcome with increased mortality is associated with delay in initiating treatment.

4. False. Rash typically starts on the hands/wrists and feet/ankles. Involvement of the palms and soles is classic.

5. c

6. b


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