Ehrlichia canis in a dog with large granular lymphocytosis, thrombocytopenia, and dysproteinemia
Ehrlichia canis in a Dog with Large Granular Lymphocytosis, Thrombocytopenia, and Dysproteinemia
Canine monocytic ehrlichiosis (CME) is caused by Ehrlichia canis, a Gram-negative obligate intracellular
coccus bacterium. The organism is transmitted by the brown dog tick, Rhipicephalus sanguineus, which
is infected transstadially (via a blood meal from an infected dog) when the organism is in either the
larvae or nymph form. It then transmits the bacterium to an uninfected dog when the organism is in
either the nymph or adult form. E. canis targets monocytes, in which it replicates and forms a morula,
but can be difficult to visualize on cytological samples. As a result, various serological tests, including
IFA, PCR, and/or Western blot are often used as diagnostic tools in the absence of the demonstration of
the organism using cytology. CME has various presentations, including acute, subacute, and chronic
phases. A common finding amongst all is thrombocytopenia, believed to be mediated by platelet-
associated IgG and antibodies that recognize platelet proteins in dogs infected with E. canis. Likewise,
hyperglobulinemia, hypoalbuminemia, and a polyclonal gammopathy may be seen in affected
individuals. In chronic forms of the disease, bone marrow suppression may be seen, resulting in
pancytopenia and hemorrhage. Dogs in the early stages of disease may have a CBC which demonstrates
lymphocytosis with cell granularity typical of lymphocytic leukemia. Treatment consists of tetracycline or
doxycycline, and improvement of thrombocytopenia is used as an indicator of successful treatment.
PATIENT HISTORY AND PHYSICAL EXAMINATION FINDINGS
A 7-year old, spayed female, mixed breed dog presented to the Kansas State University Veterinary
Teaching Hospital for evaluation of an episode of epistaxis which lasted approximately 24 hours
following blunt trauma. Epistaxis had ceased approximately 12 hours prior to presentation, but it was
noted in the animal’s history that a previous incident of mild, self-limiting epistaxis had occurred about 2
weeks prior to presentation. Ticks had been noted on the animal several months prior, though none had
been noted in the previous five months. The referring veterinarian noted thrombocytopenia,
lymphocytosis, azotemia, and hyperproteinemia, and referred the animal to KSU-VTH’s oncology service
to confirm a suspected case of lymphocytic leukemia.
On physical examination, all findings were normal, with the exception of a small amount of dried blood
noted in the nares. For further evaluation, CBC, serum biochemistry, urinalysis, and abdominal
radiographs were performed. To rule out any possible neoplastic causes for the abnormalities noted on
laboratory findings, a bone marrow aspiration was obtained, as well as antibody titers to several
common tick-borne diseases, due to the animal’s prior exposure to ticks.
LABORATORY TEST RESULTS
Parameter Value Range
White blood cells (WBC) 18.0 x 103/µL 6.0-17.0 x 103/µL
Lymphocytes 13.0 x 103/µL 1.5-5.0 x 103/µL
Platelets (PLT) 8.0 x 103/µL 200-500 x 103/µL
Packed cell volume (PCV) 30.4% 37.55%
Abnormalities (peripheral blood smear)
Large granular lymphocytes (LGLs) 50% 0-10%
Parameter Value Range
Total protein (TP) 13.5 g/dL 5.6-7.9 g/dL
Globulin 11.4 g/dL 1.8-4.2 g/dL
Albumin 2.1 g/dL 3.09-4.5 g/dL
Serum urea nitrogen (SUN) 90 mg/dL 8-30 mg/dL
Creatinine 2.9 mg/dL 0.5-1.4 mg/dL
Urine specific gravity (USG) 1.015
Blood 3-8 RBCs/HPF
Organism tested for (IgG reaction) Result
Borrelia burgdorferi Negative
Rickettsia rickettsii Negative
Ehrlichia canis Positive (1:2048)
Serum protein electrophoresis
Parameter Value Range
β-globulin 2.8 g/dL 1.3-2.7 g/dL
γ-globulin 6.4 g/dL 0.9-2.3 g/dL
Bone marrow aspiration
Parameter Value Range
Plasma cells 2.5% <2%
Lymphocytes <1% <1%
Other: mild erythroid hyperplasia, decreased megakaryocytes noted
Parameter Value Range
Platelets with surface IgG reactivity 23% 0-14%
INTERPRETATION OF RESULTS
On laboratory evaluation, both leukocytosis and lymphocytosis were noted, as well as a severe
thrombocytopenia and mild anemia. A peripheral blood smear was performed using Wright’s stain, at
which time no leukocyte- or hemoparasites were noted. Approximately 50% of lymphocytes (200
evaluated) were found to be large granular lymphocytes. Serum biochemistry showed
hyperproteinemia, hyperglobulinemia, and hypoalbuminemia, as well as increased serum urea nitrogen
(SUN) and creatinine. Urinalysis showed hematuria and proteinuria, as well as a USG of 1.015, suggestive
of glomerular proteinuria.
Due to the patient’s history of exposure to ticks, antibody titers were performed to rule out Lyme
disease, Rocky Mountain Spotted Fever, and Ehrlichia as possible causes of laboratory abnormalities.
Both titers for B. burdorferi (Lyme) and R. rickettsii (RMSF) were negative, but the titer for E. canis was
positive at 1:2048 (positive test is >1:128). PCR for E. canis using a whole blood sample was performed,
but was negative. Serum protein electrophoresis show a mild increased in β-globulin, as well as an
increase in γ-globulin, indicating the presence of a polyclonal gammopathy in the patient.
Using flow cytometry, it was noted that 23% of platelets had surface reactivity to IgG, indicative of an
immune-mediated thrombocytopenia. A bone marrow aspiration, thoracic radiographs, and abdominal
ultrasound were also performed to rule out the possibility that a neoplastic process was responsible for
the laboratory abnormalities. Upon evaluation of the bone marrow aspirate, a mild erythroid
hyperplasia was noted, as well as decreased megakaryocyte and increased plasma cell counts.
Lymphocyte count was within normal limits. Thoracic radiographs were unremarkable, but ultrasound
revealed hyperechogenicity at the renal cortices, indicative of possible glomerulonephritis or
While the animal was referred on the basis of suspected neoplasm, a large granular lymphocytic
leukemia was unlikely due to the presence of hyperglobulinemia, thrombocytopenia, and suspected
glomerulonephritis. This, in conjunction with the absence of fever and a history of tick exposure, suggest
a case of chronic canine monocytic ehrlichiosis (CME). Upon performing antibody titers for common tick-
borne diseases, a strongly positive (1:2048) result for Ehrlichia canis was noted. Despite a negative PCR
using whole blood for E. canis, it is still believed that the patient was suffering from ehrlichiosis, with the
belief that the PCR was negative due to possible sequestration of the organism in the spleen or other
sites in the body.
Due to this suspicion, the animal was treated using doxycycline at a dose of 6 mg/kg, given PO q12h, as
well as prednisone at a dose of 2 mg/kg, given PO q24h. At a 2-week recheck, CBC showed that the
anemia as well as leuko- and lymphocytoses had resolved, and the count of large granular lymphocytes
had decreased to 10% (normal 0-10%). Thrombocytopenia was still present, though platelet numbers
had increased (to 45.0 x 103/µL, normal 200-500 x 103/µL), suggesting that the issue was resolving. As a
result, treatment with doxycycline was continued for another two weeks, and prednisone was continued
for one week at a dose of 1 mg/kg, given PO q24h, after which both were ceased.
At a 4-week recheck, all CBC values had returned to normal. Serum biochemistry showed that azotemia
was still present, but resolving (SUN = 77 mg/dL, creatinine = 2.2 mg/dL). Additionally, hyperproteinemia
(10.1 g/dL), hyperglobulinemia (7.5 g/dL), and hypoalbuminema (2.6 g/dL) were still present, but
resolving. At this time, an increase in ALT (576 U/L, normal 13-79 U/L) and increased ALP (390 U/L,
normal 12-122 U/L) were noted. The owner declined further evaluation of the liver, and no urinalysis
was performed at this time. The antibody titer for E. canis was performed again, and was still positive at
1:2048, though flow cytometry showed only a 10% platelet surface reactivity to IgG, which could be the
result of the increased total platelet concentration (dilutional effect). Several months later, the patient
was still doing well.
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Jan. 18, 2020
Nov. 18, 2015
Case study review, written for veterinary clinical pathology (VPA 5448) at RUSVM.