Ehrlichiosis

Key Features

Essentials of Diagnosis

• 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

General Considerations

• 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

Clinical Findings

Symptoms and Signs

• 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

Differential Diagnosis

• 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

Diagnosis

• 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

Treatment

• 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

Outcome

Complications

• 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

Prognosis

• Response to therapy should ...