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Key Features

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Essentials of Diagnosis
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  • Residing or travel in endemic area when ticks are active

  • Tick bite noted (~75%)

  • Fever, headache, rash (~67%), gastrointestinal symptoms

  • Leukopenia, thrombocytopenia, elevated serum transaminases, hypoalbuminemia

  • Definitive diagnosis by specific serology

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General Considerations
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  • Infection caused by Ehrlichia chaffeensis

    • The reservoir hosts are probably wild rodents, deer, and sheep; ticks are the vectors

    • Most cases caused by this agent are reported in the south-central, southeastern, and middle Atlantic states (Arkansas, Missouri, Oklahoma, Kentucky, Tennessee, and North Carolina are high-prevalence areas)

    • Almost all cases occur between March and October

    • Has a predilection for mononuclear cells; thus diseases are called human monocytic ehrlichiosis

  • Infection caused by Anaplasma phagocytophilum and Ehrlichia ewingii

    • Cases are seen in the upper Midwest and Northeast (Connecticut, Wisconsin, Minnesota, and New York are high-prevalence areas)

    • Anaplasmosis also occurs in the western United States

    • Produce intracytoplasmic inclusions in granulocytes; thus diseases are called human granulocytic ehrlichiosis

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Clinical Findings

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Symptoms and Signs
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  • Usual incubation period is 5–21 days

  • Fever is universally present

  • Abdominal pain, anorexia, nausea, and vomiting are reported by most patients

  • Chills, photophobia, conjunctivitis, and myalgia occur in more than half of patients.

  • Physical examination reveals rash, mild adenopathy, and hepatomegaly

  • In children without a rash, infection may present as a fever of unknown origin.

  • Characteristics of rash

    • Occurs in ~50% of children with monocytic ehrlichiosis and is less common in granulocytic ehrlichiosis

    • May be erythematous, macular, papular, petechial, scarlatiniform, or vasculitic

  • Meningitis occurs

  • Interstitial pneumonitis, acute respiratory distress syndrome, and renal failure occur in severe cases

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Differential Diagnosis
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  • Septic or toxic shock

  • Other rickettsial infections (especially Rocky Mountain spotted fever)

  • Colorado tick fever

  • Leptospirosis

  • Lyme borreliosis

  • Relapsing fever

  • Epstein-Barr virus, cytomegalovirus, viral hepatitis

  • Kawasaki disease

  • Systemic lupus erythematosus

  • Leukemia

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Diagnosis

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  • Leukopenia with left shift, lymphopenia, thrombocytopenia, and elevated aminotransferase levels

  • Hypoalbuminemia and hyponatremia are common

  • Disseminated intravascular coagulation can occur in severe cases

  • Anemia occurs in one-third of patients

  • Cerebrospinal fluid pleocytosis is common

  • Specific polymerase chain reaction testing can provide an early diagnosis

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Treatment

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  • Asymptomatic or clinically mild and undiagnosed infections are common in some endemic areas

  • If left untreated, disease may last several weeks

  • Doxycycline, 2 mg/kg every 12 hours (IV or PO; maximum 100 mg per dose) for 7–10 days, is the treatment of choice

  • Treatment should not be delayed in patients in whom disease is suspected

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Outcome

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Complications
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  • One-quarter of hospitalized children require intensive care

  • Meningoencephalitis and persisting neurologic deficits occur in 5%–10% of patients

  • Immune compromise and asplenia are risk factors for severe disease

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Prognosis
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  • Response to therapy should be evident in 24–48 hours

  • Deaths are uncommon in children

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