Human Monocytic Ehrlichiosis

1. See Also
   1. Human Granulocytic Ehrlichiosis
   2. Vector Borne Disease
   3. Prevention of Tick-borne Infection
   4. Tick Removal
2. Pathophysiology
   1. Carried by Lone star tick (Amblyomma americanum)
   2. Small gram-negative organisms
      1. Pleomorphic
      2. Obligate intracellular organisms
   3. Organisms causing Human Monocytic Ehrlichiosis
      1. Ehrlichia chaffeensis
      2. Ehrlichia ewingii
3. Epidemiology
   1. Majority of cases occur April to September
      1. Highest Incidence in June and July
   2. U.S. regions affected
      1. South and Southeast
      2. Midwest
   3. Woods exposure
4. Symptoms (Occur 7-10 days after tick bite)
   1. Common Initial Symptoms
      1. Fever
      2. Shaking chills
      3. Myalgia
      4. Headache
   2. Other symptoms
      1. Nausea and Vomiting
      2. Abdominal Pain
      3. Diarrhea
      4. Cough
      5. Confusion
5. Signs: Rash (occurs in <50% of patients)
   1. Involves trunk
   2. Spares hands and feet
   3. Not associated with tick bite site
6. Labs
   1. Complete Blood Count
      1. Leukopenia
      2. Thrombocytopenia
   2. Liver transaminases increased
      1. Aspartate Aminotransferase (AST) increased
      2. Alanine Aminotransferase (ALT) increased
   3. Cerebrospinal Fluid
      1. Lymphocytic Pleocytosis
      2. Increased CSF Protein
   4. Ehrlichiosis Serology
      1. Positive two weeks after onset
      2. Used for confirmation, not for diagnosis
      3. Anticipate a fourfold rise in Antibody titers
         1. Minimum peak 1:64
         2. Maximum peak 1:128 or higher dilution
   5. Other variably present laboratory findings
      1. Increased Erythrocyte Sedimentation Rate (ESR)
      2. Increased Blood Urea Nitrogen (BUN)
      3. Increased Serum Creatinine
7. Management
   1. General
      1. Antibiotics for two weeks (minimum of 5-7 days)
      2. Continue for at least 3 days after fever subsides
   2. Agents
      1. Doxycycline 100 mg bid or
      2. Chloramphenicol or
      3. Rifampin
8. Prevention
   1. See Prevention of Vector-borne Infection
9. Reference
   1. Fritz (1998) Infect Dis Clin North Am 12:123-36
   2. Glushko (1997) Postgrad Med 101(6):225-30
   3. McQuiston (1999) Emerg Infect Dis 5:635-42
   4. Standaert (1995) N Engl J Med 333:420-5
   5. Weinstein (1996) Am Fam Physician 54(6):1971-6
   6. (1994) Ann Intern Med 120:730,6
   7. (1995) MMWR Morb Mortal Wkly Rep 44:593-5