Ehrlichiosis, Emergency Medicine

Basics

Description

Tick-borne human infection presenting as a nonspecific febrile illness
Several forms of ehrlichiosis exist; 2 predominate in North America
- Human monocytic ehrlichiosis (HME), 1st described in 1987:
  - Vector tick: Amblyomma americanum (lone star tick)
  - Geographic range: Central, southern, and mid-Atlantic states, with range expanding to parts of New England
- Human granulocytic ehrlichiosis or human granulocytic anaplasmosis (HGE or HGA), 1st described in 1994:
  - Vector tick: Ixodes scapularis (deer tick)
  - Geographic range: East Coast, mid-Central States, and Pacific Northwest (same areas as Lyme disease which is more common in US than HME)
All are tick borne but have different vectors and geographic ranges. Other species have been reported, but at present HME and HGE are the important ehrlichial human pathogens.

Etiology

2 distinct species of obligate intracellular organisms
The taxonomy of these pathogens has changed in recent years as more DNA and ribosomal RNA data become available.
HME is caused by the organism Ehrlichia chaffeensis.
HGE/HGA is caused by Anaplasma phagocytophila (a new name as of 2002).
The vasculitis found in Rocky Mountain spotted fever (RMSF) is usually not present.
A 3rd type may also be encountered, caused by Ehrlichia ewingii, which has the tick vector of the lone star tick. Clinically similar to HME.
Compared with RMSF, older individuals are usually affected, commonly >40 yr of age.

Diagnosis

Signs and Symptoms

Signs and symptoms of HME and HGE/HGA are similar.
Many patients who are infected undergo asymptomatic seroconversion.
The spectrum reported may overrepresent the more severely affected patients.
With any tick-borne infection, patients can be coinfected by more than 1 pathogen from the same tick bite:
- May have a complicated presentation of 2 different diseases
1/4 of children have severe disease.

History

The season and other epidemiologic factors are important in diagnosing tick-borne diseases:
- Most commonly present from April to October
- Variability is likely owing to changes in weather patterns from year to year and from region to region.
Symptom onset from 1-2 wk (median 9-10 days) following the tick bite:
- Bite of the larger lone star tick is more likely to be recalled by the patient than that of the smaller deer tick.
Abrupt onset of:
- Fever
- Chills
- Headache
- Myalgias
- Malaise
Rash:
- HME (35-60% of cases)
- HGE or HGA (~5-10% of cases)
- Often delayed and may be variable
Symptoms may relate to complications of ehrlichiosis, such as:
- ARDS
- Renal failure
- Hypotension and shock
- Rhabdomyolysis
- GI disturbances
- CNS or peripheral nervous system (PNS) involvement, such as encephalopathy and meningitis as well as seizures
- DIC
- Immunocompromised patients have more severe complications.

Physical Exam

Fever
Rash:
- May be macular, maculopapular, or petechial
- May be absent during 1st wk of illness
- Usually involves trunk and spares hands and feet
Lymphadenopathy
Hepatosplenomegaly
Neurologic findings:
- Abnormal mental status
- Meningismus
- Nystagmus
Pulmonary findings (rales, rhonchi) depending on pulmonary complications

Fever, headache, and rash present in 48%
Lymphadenopathy in 45%

Ehrlichiosis is a potentially fatal tick-borne illness that is usually diagnosed clinically.
Consider this diagnosis in all patients with nonspecific febrile illnesses, especially during the warm months of the year, and definitely if there is a history of tick bite.
The Centers for Disease Control and Prevention (CDC) define the illness as fever with 1 or more of the following: Headache, myalgia, anemia, leukopenia, thrombocytopenia, or elevation of serum transaminase; + serologic evidence of 4-fold change in IgG specific antibody by IFA or detection of specific target by PCR assay, demonstration of antigen on biopsy/autopsy sample, or isolation of organism in cell culture.

Diagnosis Tests & Interpretation

Lab

CBC:
- Leukopenia
- Thrombocytopenia
- Anemia
Hepatic transaminases:
- Often elevated 2-6 times normal
Indirect immunofluorescence antibody test, specific for HME and HGA
- Usual test available
- Threshold for a positive test is usually made by the individual lab testing the serum.
- 94-99% sensitive when 2nd sample obtained over 14 days from onset of illness
Wright stain of peripheral blood:
- Morula may be seen:
  - Small intracytoplasmic ehrlichial DNA inclusion bodies
  - Diagnostic
  - Sensitivity of seeing morulae depend on who is looking, for how long, and the immunologic competence of the patient.
  - Found more commonly in HGE/HGA (~50%) than in HME (~10-15%)
Culture and PCR for HEM and HGA
- Not routinely available
Antibody titer tests:
- Not available in real time
Lumbar puncture
- Pleocytosis with predominance of lymphocytes and increased total protein

Imaging

Head CT for encephalopathy
CXR for fever/dyspnea

Differential Diagnosis

Most tick-borne illnesses:
- RMSF
- Lyme disease
- Babesiosis
Many viral and bacterial infections and numerous other infectious diseases, especially early in their course, can initially present with an undifferentiated febrile illness similar to ehrlichiosis.
Mononucleosis
Thrombotic thrombocytopenia purpura
Hematologic malignancy
Cholangitis
Pneumonia

Treatment

Initial Stabilization/Therapy

ABCs

Ed Treatment/Procedures

Initiate antibiotics:
- Doxycycline:
  - Drug of choice
  - Children who are affected should also receive doxycycline. 14 days of treatment does notappear to cause significant discoloration of permanent teeth. The risks and benefits in children <9 yr old should be specifically discussed with parents.
  - Treatment should be continued for at least 3 days past defervescence for a min. total course of 7 days. Severe or complicated disease requires a longer course.
- Rifampin for:
  - Pregnant patients
  - Allergy to doxycycline
  - Mildly affected children <9 yr of age
  - Patients who are pregnant, allergic to doxycycline, or mildly affected can be given rifampin for 7-10 days.
Initiate therapy for other tick-borne diseases that may have been cotransmitted.

Medication

Doxycycline:

Adults: 100 mg IV/PO q12h for 10 days or for 3-5 days after defervescence.
Children (severely affected): 4 mg/kg q12h IV/PO up to max. of adult dose; older children can be dosed as adult.

Despite the fact that doxycycline is generally contraindicated in patients <9 yr old, it is the drug of choice in young children who are severely affected by ehrlichiosis. In less affected children, rifampin has been used successfully.
Rifampin can be used to treat pregnant women with ehrlichiosis. When life-threatening disease is present, doxycycline may be considered.

Follow-Up

Disposition

Admission Criteria

Significant comorbidities/severely affected
Cannot take PO antibiotics
Immunosuppressed patients
E. chaffeensis (HME) has a case fatality rate up to 3%.

Discharge Criteria

Healthy appearing
Symptoms typically last 1-2 wk; recovery occurring without sequelae.
Long-term neurologic complications have been reported.

Issues for Referral
Severe disease or presence of complications

Additional Reading

American Academy of Pediatrics. In: Pickering LK, Baker CJ,Kimberlin DW, et al., eds. Red Book: 2009 Report of the Committee onInfectious Diseases. 28th ed. Elk Grove, IL: AAP, 2009.
Bakken JS, Dumler S. Human granulocytic anaplasmosis. Infect Dis Clin NorthAm. 2008;22:433-448.
Edlow JA. Bulls Eye: Unraveling the MedicalMystery of Lyme Disease. 2nd ed. New Haven, CT: Yale University Press, 2004.
Olano JP, Walker DH. Human ehrlichioses. Med Clin North Am. 2002;86:375-392.
Ramsey AH, Belongia EA, Gale CM, et al. Outcomes of treated human granulocytic ehrlichiosis cases. Emerg Infect Dis. 2002;8(4):398-401.
Schutze GE, Buckingham SC, Marshall GS, et al. Human monocytic ehrlichiosis in children. Pediatr Infect Dis J. 2007;26:475-479.
Stone JH, Dierberg K, Aram G, et al. Human monocytic ehrlichiosis. JAMA. 2004;292:2263-2270.

Codes

ICD9

082.40 Ehrlichiosis, unspecified
082.41 Ehrlichiosis chafeensis [E. chafeensis]
082.49 Other ehrlichiosis
082.4 Ehrlichiosis

ICD10

A77.40 Ehrlichiosis, unspecified
A77.41 Ehrlichiosis chafeensis [E. chafeensis]
A77.49 Other ehrlichiosis
A77.4 Ehrlichiosis

SNOMED

77361002 Ehrlichiosis (disorder)
359747000 Human ehrlichiosis due to Ehrlichia chaffeensis (disorder)
85708001 Human anaplasmosis due to Anaplasma phagocytophilum (disorder)
441554001 Infection by Ehrlichia ewingii

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