Page 629 - Cote clinical veterinary advisor dogs and cats 4th

286 Ehrlichiosis, Monocytic

ASSOCIATED DISORDERS • After attaching to a susceptible dog for hyperglobulinemia are hallmarks of clinical
• Co-infection with other tick-borne pathogens as little as 3 hours, the tick transmits the infection. (from immune-
VetBooks.ir Anaplasma platys, Babesia canis, Rickettsia • After inoculation, the organism invades mediated destruction, sequestration, or
organism in its saliva.
○ Thrombocytopenia
○ Brown dog tick (vector for E. canis):
decreased production): 90% of cases
rickettsii, Hepatozoon canis
lymphocytes and monocytes/macrophages,
○ Lone star tick (vector for E. chaffeensis):
of chronic inflammatory disease, or bone
membrane-bound vacuoles or morulae that
Ehrlichia ewingii (found in Panola multiplies intracellularly, and forms ○ Anemia (as a result of hemorrhage, anemia
Mountain State Park, GA), Cytauxzoon contain several individual bacteria. A positive marrow suppression)
felis (cats), Francisella tularensis, ± R. antibody titer is first detected 7-28 days after ○ Neutropenia or neutrophilia
rickettsii inoculation. ○ Lymphocyte count variable; marked
• During the acute phase of infection, few granular lymphocytosis is common with
Clinical Presentation organisms may be found in circulating chronic CME and must be distinguished
DISEASE FORMS/SUBTYPES monocytes and lymphocytes, and the spleen from a lymphoid leukemia.
The incubation period is 1-3 weeks after tick is thought to harbor the infection. ○ Identification of morulae in mononuclear
inoculation, after which three phases of infec- • During the subclinical phase, immune cells is rare but strongly supports the
tion can occur: stimulation results in seropositive diagnostic diagnosis.
• Acute phase (lasts 1-4 weeks): dogs show test results, even though the animal is not ○ Hyperglobulinemia, typically a polyclonal
clinical signs but recover. Untreated animals overtly ill. gammopathy; monoclonal gammopathy
recover spontaneously but progress to the • During the chronic phase of infection, direct can occur with chronic CME, and this
subclinical phase and are carriers of the agent; damage done by the organism and damage finding along with bone marrow plasma-
treated dogs clear the organism. Host and resulting from the host’s immune response cytosis must not lead to a misdiagnosis
pathogen factors influence severity of acute can cause several clinical and hematologic of multiple myeloma.
illness. abnormalities, notably severe bone marrow ○ Nonspecific increases in liver enzyme
• Subclinical phase (lasts months to many suppression and pancytopenia (often fatal). activities and blood urea nitrogen (BUN)
years): no clinical signs; some dogs remain • CME is a multisystemic disease with many and hypoalbuminemia are common.
in this subclinical state for life, whereas others clinical manifestations due to the presence ○ Proteinuria is possible in the chronic phase
progress to the chronic phase. of organisms in various tissues and the host’s due to glomerulonephritis.
• Chronic phase: various manifestations of immune response. Host response to newly • Point-of-care serologic tests: SNAP 4Dx Plus
clinical disease (well documented for E. exposed or altered antigens can worsen clini- detects antibodies to E. canis, E. chaffeensis,
canis, likely for E. chaffeensis in dogs) cal signs directly and by the formation and and E. ewingii; WITNESS Ehrlichia detects
deposition of immune complexes in glom- antibodies to E. canis.
HISTORY, CHIEF COMPLAINT eruli, synovial membranes, and meninges ○ Excellent for routine screening and sup-
• Infection is often recognized in healthy dogs (causing nephropathies, arthropathies, and portive evidence for chronic infection
by screening tests. neuropathies, respectively). ○ In acute infections, antibody levels may
• With illness, the most common complaints not be detectable: if point-of-care test
are nonspecific: lethargy, anorexia, weight DIAGNOSIS result is negative in a case with signs
loss, bleeding tendencies. suggesting CME, PCR is recommended.
• Additional signs during the chronic phase Diagnostic Overview ○ The SNAP antibody reaction does not
may be related to anemia (e.g., weakness, Dogs with consistent clinical findings and distinguish between the three Ehrlichia
collapse), neurologic signs, or renal disease thrombocytopenia should be suspected of species, but geographic region and
(e.g., polyuria/polydipsia). having CME and/or other related vector-borne clinical presentation can help determine
• Because clinical manifestations occur weeks agents and should be tested accordingly, regard- which infection is more likely. Although
to years after tick inoculation, a history of less of known tick exposure. Confirmation of CME can cause acute or chronic illness
tick exposure is variable. infection requires finding morulae in circulating (which may have very different types of
monocytic cells (rare), a positive point-of-care presentation), E. ewingii usually causes
PHYSICAL EXAM FINDINGS or laboratory based serologic test, or polymerase acute polyarthropathy or neurologic signs
• Throughout the subclinical phase and chain reaction (PCR) analysis. (p. 393).
sometimes during the acute or chronic disease ○ It is crucial to remember that in areas
phases, exam findings are unremarkable. Differential Diagnosis endemic for any of the Ehrlichia spp, a
• If abnormalities are present during illness • Co-infection with other tick-borne organ- positive antibody test result does not prove
(i.e., acute or chronic phase), common isms: other Ehrlichia spp, Anaplasma spp, that ehrlichiosis accounts for the observed
findings include fever (especially in acute Bartonella spp, Rickettsia spp, Borrelia spp clinical signs in a given patient. The animal
phase), lymphadenopathy, splenomegaly, • Immune-mediated causes of peripheral could be in the subclinical phase of CME
epistaxis, and petechiae. cytopenias, polyarthritis, meningitis, and (or recovered from prior infection with
• Other potential abnormalities include pallor, glomerulonephritis another species of Ehrlichia) and therefore
ocular hemorrhage, lameness, and neurologic • Large, granular lymphoid leukemia: like antibody positive, but the current disease
signs. CME, it can be associated with high periph- may be caused by something entirely
eral granular lymphocytosis (6000-17,000 unrelated to the infection.
Etiology and Pathophysiology cells/mcL).
• E. canis is transmitted by the brown dog • Multiple myeloma: like CME, it can be Advanced or Confirmatory Testing
tick (Rhipicephalus sanguineus) and E. associated with monoclonal or biclonal gam- • Buffy coat smears: enhanced detection of
chaffeensis by the lone star tick (Amblyomma mopathy and bone marrow plasmacytosis, morulae in circulating mononuclear cells
americanum). as well as thrombocytopenia. compared to regular blood smears; still
• Because transovarial transmission in these uncommon findings, except in animals with
ticks has not been demonstrated, the tick Initial Database acute disease
must acquire the infection at the larval or • CBC, serum biochemical profile, urinalysis: ○ Finding morulae in monocytic cells
nymph state from a mammalian reservoir during subclinical phase, routine laboratory confirms the dog as having E. canis or
host. tests are unremarkable. Cytopenias and E. chaffeensis.

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