Rocky Mountain Spotted Fever
B. Denise Hemby and Theresa M. Campo
Definition
A.Rocky Mountain spotted fever (RMSF) is a serious bacterial tick-borne disease that can be deadly if not treated early. The cause is the organism Rickettsia rickettsii and it is spread by several species of ticks in the United States, with the most common tick being Dermacentor variabilis (American dog tick). The organism is endemic in parts of North, Central, and South America, especially in the southeastern and south. RMSF has been described as a wolf in sheep’s clothing
and the great imitator
of other disease processes. The hallmark is a petechial rash beginning on the palms of the hands and soles of the feet.
B.Although its clinical manifestations and treatment are well known, RMSF still causes significant mortality and morbidity. The current mortality rate is 1.4% mostly due to delay in diagnosis and treatment. In the United States, RMSF is a reportable disease. Mortality rate in untreated cases is 20% to 25%. Mortality rates can be as low as 5% with proper antibiotic therapy and as high as 70% in untreated elderly people.
Incidence
A.RMSF is the most common cause of fatal tick-borne illness in the United States. Although RMSF is more common in rural and suburban locations, it does occur in urban areas. The highest incidences are in the southeastern United States tick belt (the South Central region) and selected areas of the Northeast. In the northern United States, infections commonly occur in the spring. However, in the South, cases may occur at any time of the year, including winter.
B.People of all ages can be infected. Caucasians have twice the incidence of African Americans. African Americans have a higher case-fatality rate, possibly due to the difficulty of distinguishing the rash in highly pigmented skin.
C.The incidence of RMSF is highest among adults aged 60 to 69 years (3.1 cases/million persons) and children aged 5 to 9 (estimated 3.3 cases/million persons)
D.RMSF is the only tick-borne disease that can directly cause heart failure secondary to myocarditis.
Pathogenesis
A.R. rickettsii is the infectious agent and is transmitted by a tick vector. R. rickettsii is a small, gram-negative, obligate, intracellular coccobacillus. The organism is spread through the body via blood and the lymphatic system. The bacteria also infects rodents, squirrels, and chipmunks. Up to one-third of patients with proven RMSF do not recall a recent tick bite or tick contact. RMSF is not transmitted by person-to-person contact.
B.Ticks can become infected by transmission from an infected animal during feeding or from mother to offspring. Infection can occur through contact with tissue and fluids from the tick. The incubation period ranges from 2 to 12 days after either the tick bite or contamination but usually occurs around 1 week or 7 days and depends on the amount of contamination from the tick.
C.Principal recognized vectors:
1.D. variabilis (American dog tick).
2.Dermacentor andersoni (Rocky Mountain wood tick).
3.Amblyomma americanum (Lone Star tick).
4.Rhipicephalus sanguineus (brown dog tick).
Predisposing Factors
A.Outdoor activities (hunting, hiking, camping).
B.Tick bite: The tick must attach and feed for 6 to 10 hours before transmitting the infection.
C.Age is not a predisposing factor, but the disease is more common in children and young adults.
D.Exposure to heavy brush areas.
E.Contact with dogs and other animals with ticks.
F.Transmission has occurred on rare occasion by blood transfusion.
Common Complaints
In the early phase, most patients have nonspecific signs and symptoms. The classic triad of fever, headache, and rash may be present in less than 5% in the first 3 days but increases to 60% to 70% by the second week after tick exposure:
A.Fever (>102°F).
B.Headache—frequently severe.
C.Myalgias.
D.Rash—usually (90%) occurs between 3 and 5 days of illness. The typical RMSF rash begins as a pink maculopapular eruption on the ankles and wrists. The rash then spreads both centrally and to the palms of hands and soles of the feet. By the fourth day, the rash spreads centripetally and becomes petechial and papular. Hemorrhagic, ulcerated lesions may follow. In a small percentage, onset of the rash is delayed (past 5 days) and/or is atypical (e.g., confined to one body region). Urticaria and pruritus are not characteristic of RMSF, and their presence makes the diagnosis unlikely.
Other Signs and Symptoms
A.Periorbital edema—key finding in children.
B.Deep nonproductive cough at the time of the rash.
C.Edema.
D.Bleeding.
E.Conjunctivitis with or without photophobia.
F.Retinal abnormalities.
G.ECG abnormalities.
H.Seizures.
I.Dehydration.
J.Malaise.
K.Nausea without vomiting.
L.Altered mental status.
Potential Complications
A.Disseminated intravascular coagulation (DIC).
B.Noncardiogenic pulmonary edema.
C.Acute renal failure (ARF).
D.Myocarditis/heart failure: Usually a cause of death.
E.Skin necrosis and gangrene (fingers, toes, elbows, ears, and scrotum).
F.Seizures.
G.Encephalopathy.
H.Peripheral neuropathy.
I.Hearing loss.
J.Cerebellar and vestibular dysfunction.
K.Bowel and bladder incontinence.
Subjective Data
A.Review the onset, course, and duration of symptoms.
B.Elicit information about a recent tick bite or removal.
C.Ask the patient about any recent outdoor activities such as camping, hiking, gardening, or other activities and travel, especially to endemic areas. Less than half of the people infected remember a tick bite.
D.Rule out similar symptoms in other family members.
E.Review thorough history of medications
F.Review any history of rash and course of spread.
G.Elicit a history of mental or neurologic changes, including seizures.
H.Rule out other symptoms such as arthritis, memory loss, and distal paraesthesia.
I.Review the patient’s recent history of blood transfusion.
Physical Examination
A.Check temperature, pulse, respirations, and blood pressure. Elevated temperature (fever >102°F) is the most common symptom.
B.Inspect:
1.Conduct an ear, nose, and throat exam.
2.Inspect the skin, especially on the wrist, palms, ankles, and soles of the feet. The face is generally spared from the rash. Rash is a major diagnostic sign that can appear on the first day of infection. Maculopapular rash appears 2 to 6 days after onset of fever
3.Note the presence of petechiae. The rash may blanch and appear macular in the early phase.
4.Conduct an eye examination; evaluate periorbital edema and petechial conjunctivitis.
C.Auscultate:
1.Perform complete heart evaluation.
2.Auscultate all lung fields.
D.Palpate:
1.Palpate all lymph nodes.
2.Palpate the mastoid bones.
E.Neurologic examination:
1.Assess level of consciousness (LOC).
2.Evaluate the patient for signs of meningeal irritation, such as nuchal rigidity and positive Brudzinski’s and Kernig’s signs (see Figures 19.1 and 19.2).
Diagnostic Tests
A.Indirect immunofluorescence antibody (IFA). Antibody titers: A four-fold rise in antibody titer is the diagnostic gold standard for RMSF:
1.Antibodies typically appear 7 to 10 days after the onset of the illness.
2.85% will not have detectable antibody titers during first week of illness.
B.Complete blood count (CBC) with differential. Platelet count: As the illness progresses, thrombocytopenia becomes more prevalent and may be severe. White blood cell (WBC) can be normal.
C.Coagulation panel—prothrombin time (PT)/partial thromboplastin time (PTT)/international normalized ratio (INR).
D.Chest x-ray.
E.ECG.
F.Comprehensive metabolic panel.
G.Liver function studies.
H.PPCR.
I.Bilirubin.
J.Skin biopsy: 3 mm punch biopsy.
K.Lumbar puncture may be indicated if suspected meningitis and/or other neurologic signs.
L.Rickettsial blood cultures are highly sensitive and specific; however, they require specialized laboratories.
Differential Diagnoses
A.RMSF.
B.RMSF is commonly mistaken for an undifferentiated viral illness during the first few days of illness. Consider RMSF if other signs and symptoms support a diagnosis, even if a rash is not present.
C.Viral meningitis.
D.Ehrlichiosis.
E.Tularemia.
F.Anaplasmosis.
G.Lyme disease (LD).
H.Mononucleosis.
I.Atypical measles.
J.Viral hepatitis..
K.Parvovirus B19 (fifth disease).
Plan
A.General interventions:
1.Early treatment is necessary; never delay initiation of antimicrobial treatment to confirm clinical suspicion of the disease. This is a life-threatening disease. Antibiotics are less likely to prevent fatal outcome from RMSF if started after day 5 of symptoms. Close monitoring is necessary.
2.Antibiotic therapy (see Pharmaceutical therapy
of this section). If penicillin or a cephalosporin is administered empirically in the first few days of the illness, the subsequent rash may be incorrectly diagnosed as a drug reaction.
3.Hospitalization should be considered for most patients. Mild cases may be treated as outpatient. RMSF can progress rapidly.
B. 
See Section III: Patient Teaching Guide Rocky Mountain Spotted Fever and Removal of a Tick
:
1.RMSF is not transmissible by person-to-person contact; therefore, isolation is not necessary.
2.Relapse of the illness may occur; the patient should report recurrence of symptoms immediately.
3.Patients who report tick bites should be advised to inform their healthcare provider if any systemic symptoms, especially fever and headache, occur in the following 14 days.
4.All pets should be treated for ticks.
C.Pharmaceutical therapy:
1.Drug of choice: Doxycycline 100 mg orally or intravenous (IV) every 12 hours for 5 to 7 days for adults.
2.Patients younger than 8 years: Doxycycline is not recommended for mild to moderate infection:
a.Older than 8 years and less than 45 kg: Loading dose 4.4 mg/kg/d PO/IV BID for 1 day.
b.Maintenance dose 2.2 to 4.4 mg/kg/d PO/IV BID.
Patients should be treated for at least 3 days after fever subsides and until there is evidence of clinical improvement. Minimum course of therapy is 5 to 7 days.
c.If pregnant or doxycycline allergy—chloramphenicol.
d.Most experts consider the risk of morbidity from rickettsia diseases greater than the minimal risk of dental staining from one short course of doxycycline.
3.Alternative drug therapy: Chloramphenicol (Chloromycetin):
a.Chloramphenicol requires frequent serum platelet counts and CBCs.
b.Not available in oral form in the United States.
c.Use of chloramphenicol is associated with a higher risk of fatal outcome and persons treated with it have a greater risk of death compared to doxycycline.
4.Prophylactic therapy with doxycycline or another tetracycline is not recommended following tick exposure.
Follow-Up
A.See the patient 24 to 48 hours after initial visit and again at the end of antibiotic therapy (unless following lab for chloramphenicol therapy). RMSF progresses rapidly. Approximately 10% of outpatients are subsequently admitted to the hospital.
B.Several rickettsial diseases, including RMSF, are nationally notifiable diseases and should be reported to state and local health departments.