A tickborne febrile illness most commonly characterized by acute
onset, accompanied by headache, myalgia, rigors and/or malaise. Clinical laboratory
findings may include intracytoplasmic microcolonies (morulae) in leukocytes of
peripheral smear, cerebrospinal fluid (CSF), or bone marrow aspirate or biopsy,
cytopenias (especially thrombocytopenia and leukopenia), and elevated liver enzymes
(especially alanine aminotransferase or aspartate aminotransferase).
There are two clinically similar yet serologically distinct
forms of ehrlichiosis: a) human granulocytic ehrlichosis (HGE), caused by infection
with an Ehrlichia equi-like agent and found primarily in the upper midwest
and northeast, and b) human monocytic ehrlichiosis (HME) caused by Ehrlichia
chaffeensis infection and found primarily in the southeastern quadrant of
the United States.
Laboratory criteria for diagnosis
Fourfold or greater change in antibody titer to Ehrlichia
spp. antigen by immunofluorescence antibody (IFA) test in acute- and convalescent-phase
specimens ideally taken greater than or equal to 4 weeks apart. HME diagnosis
requires E. chaffeensis and HGE currently requires E. equi or
HGE-agent antigen, or
Positive polymerase chain reaction assay. Distinct primers
are used for the diagnosis of HGE and HME, or
Intracytoplasmic morulae identified in blood, bone marrow,
or CSF leukocytes, and an IFA antibody titer greater than or equal to 64.
Case classification
Probable: a clinically compatible
case with either a single IFA serologic titer greater than or equal to 64 or intracytoplasmic
morulae identified in blood, bone marrow, or CSF leukocytes
Confirmed: a clinically compatible case that is laboratory
confirmed
Comment
All laboratory testing should be conducted by experienced personnel
with appropriate training and should include appropriate controls and reagents
necessary for accurate etiologic diagnosis. States in which cases of HGE and/or
HME have occurred may submit reports to CDC