Kim & Choice - Canine Ehrlichiosis
By Sarah Levine, VMD

Spring in Israel is a beautiful time of year, but spring also means the beginning of the tick season. Over the course of one week this March, veterinarian, Dr. Adi Yaron, was faced with two different cases of canine ehrlichiosis. This scenario is not unusual in Israel where ehrlichiosis is endemic.

His first case involved Kim, a 6-year-old female Labrador, who presented with decreased appetite and depression. Physical exam revealed all within normal limits except for a temperature of 40.5.  Blood tests were recommended and run.  Blood test results showed that Kim was suffering from leukopenia (wbc=6.2 / normal range: 8-17), neutrophilia with a left shift, mild anemia (Hct=33.3 / normal range: 37-55), and thrombocytopenia (Plt=60,000 / normal range: 150-500,000).  She also had elevated liver enzymes.

Due to financial considerations, the owner’s refused any further testing.  In Israel, the most common cause of thrombocytopenia in dogs is Ehrlichia canis. It was therefore assumed that Kim was suffering from an acute case of ehrlichiosis and she was treated with doxycycline  (10mg/kg once daily x 21 days).  Within 48 hours of instituting treatment, Kim’s condition dramatically improved, thereby suggesting that she indeed had been suffering from ehrlichiosis. No follow up blood work was run.

Choice, a 5-year-old male pitbull also presented to Dr. Yaron due to depression, weakness and inappetance for the past week that included a short bout of vomiting. The only abnormality found during physical exam was slightly enlarged submandibular lymph nodes. Blood work revealed severe leukopenia, neutrophilia with a left shift, severe nonregenerative anemia and severe thrombocytopenia.

An Ehrlichia canis serologic test was run using the ImmunoComb^® ELISA Antibody Test Kit and the results were 4+ (S score) for Ehrlichia canis. Choice was suffering from a chronic case of canine ehrlichiosis. He was immediately treated with doxycycline (10mg/kg SID x 21 days) and prednisone (2mg/kg BID x 7 days then taper off), as well as medication to protect his digestive tract from the high dose of corticosteriods. His clinical condition improved gradually after commencement of treatment and his blood work was clearly returning to normal when rechecked one week later.

Clinical Signs:
Canine ehrlichiosis usually presents with non-specific clinical signs. Symptoms seen in the acute phase include fever, anorexia, lethargy, vomiting, lymphadenomegaly, splenomegaly, weight loss and hemorrhage. In the chronic stage clinical signs may include any of the before mentioned symptoms plus mild or severe uveitis, and hemorrhage due to severe thrombocytopenia (i.e. melena, epistaxis, hyphema, petechiation or ecchymosis etc.). Thrombocytopenia and mild/moderate anemia are the most common hematologic changes seen⁽¹⁾. Other clinical signs include oculonasal discharge, lameness, dyspnea, chorioretinitis and subretinal hemorrhages⁽²⁾. Neurologic signs may be seen in the acute and chronic stages.

Diagnosis:
Diagnosis must take history of tick exposure, clinical signs, and hematologic abnormalities all into consideration. Because cases of canine ehrlichiosis often present with vague symptoms, serologic testing is an important component of diagnosis. Antibody titers may be negative in the acute phase because it takes up to 3 weeks to develop a significant titer⁽³⁾. Serology tests are often the only way to diagnose subclinical cases. A positive rising serum titer over 1:100 generally confirms diagnosis⁽¹⁾.

Other diagnostic tests that can be used are an ELSIA, indirect immunofluorescent antibody (IFA) test, and Western immunoblot analysis. Identification of E. canis in tissues and blood is done via PCR amplification with sequencing of the 16s rRNA gene^(1,4). Intracytoplasmic morulae are sometimes found in the mononuclear cells using Wright’s Giemsa stain⁽¹⁾. Of all the above-mentioned tests, serologic testing like an ELISA proves to be the most practical and user-friendly for the practicing veterinarian.

If diagnosis is made of Hepatazoan canis or Babesia canis, other diseases transmitted by Rhipicephalus sanguineus, E. canis should also be considered⁽²⁾. Co-infection is very common.

In Dr. Yaron’s case with Kim, it obviously would have been preferred to definitively diagnose her disease via serologic testing. Her general symptoms of fever, malaise and decreased appetite could have been due to almost any disease process. Her blood profile (mild anemia, thrombocytopenia, leukopenia, neutrophilia with left shift) was suggestive of but not definitive for E. canis.

Choice also presented vaguely with decreased appetite, lethargy and mild lymphadenopathy. His blood profile was suggestive of canine ehrlichiosis (severe anemia + leukopenia + thrombocytopenia). The ELISA test confirmed the suspicion that this was a case of CME, thereby allowing the appropriate treatment specific for E. canis to be instituted.  

Treatment & Prevention:
Treatment includes administration of tetracycline (20mg/kg TID) or doxycycline (10mg/kg SID) for three weeks. Immunosuppressive doses of corticosteroids can help prevent the immune mediated destruction of erythrocytes and platelets. Bone marrow stimulants can be used if necessary. Supportive treatment should be instituted as needed. Clinical response usually begins within 48 hours after commencement of doxycycline. Chronic stage cases can take longer to respond to treatment⁽³⁾.

Tick control is extremely important. By preventing the vector, one can effectively protect dogs against ehrlichiosis. CME can also be transmitted via blood transfusions⁽²⁾. Blood donors and all transfusion blood must be screened.

References:
(1)   Raskin R. (2002). Hematologic parasites. Proceedings, Western Veterinary Conference.
(2)   Baneth G., Waner T., Koplah A., Weinstein S. & Keysary A. (1996). Survey of Ehrlichia canis antibodies among dogs in Israel. The Vet. Rec., 257-259.
(3)   Couto C.G. (2000). Rickettsial Diseases. Saunders Manual of Small Animal Practice, 2nd edition. chapter 15: 126-127.
(4)   Waner T., Keysary A., Bark H., Sharabani E.& Harrus S. (1999). Canine monocytic Ehrlichiosis: An overview. Israel Journal of Veterinary Medicine, 54(4), 103-107.