A 12 year old, female spayed, poodle was referred due to anemia and thrombocytopenia. She had presented to her primary care veterinarian due to weakness and loss of appetite. An initial CBC performed by the primary veterinarian 24 hours earlier had been unremarkable at a reference laboratory. Laboratory results from presentation noted anemia (Hct 27%) and thrombocytopenia (40 k/uL), bilirubinuria. She had been started on steroid therapy at immunosuppressive doses before transfer.
At arrival saline agglutination was negative. No spherocytes were noted on blood smear evaluation however intracellular organisms were noted in the red blood cells. Review by a pathologist confirmed these organisms as a large Babesia organism. PCR testing confirmed Babesia coco.
Babesia is a protozoal erythrocytic parasite. It may infect many different mammals due to many different Babesia species (over 100). Babesia is most commonly transmitted by ticks although via contaminated blood transfusion has been documented. Babesia historically has been divided into large species (2-5 um ) and small species (1-3 um) based on intraerythrocytic size. Large type Babesia include B canis, B vogeli, B rossi, B coco and typically appear as single or paired tear-drop forms. Small type Babesia include B microti, B conradae, B microti-like and appear as signet ring form. Classical signs of babesiosis include fever, hemolytic anemia, thrombocytopenia, splenomegaly.
Examination of blood smears from peripheral capillaries may increase sensitivity of finding organisms. Antibody testing and PCR assay are also used as diagnostic options. Typical limitations such as false negatives occur with both tests. A newer PCR assay aimed at mitochondrial DNA sequencing seems to have higher sensitivity than established tests targeting 18S rRNA gene. While not commercially available either, a new ELISA for detection of Babesia antigen in the acute phase of the disease has been tested in Europe.
Therapeutic options differ between large type and small type Babesia. Imidocarb dipropionate has shown efficacy against large type organisms. A combination of atovaquone and azithromycin may be utilized with B gibsoni and B conradae. In refractory patients, doxycycline, clindamycin, and metronidazole has been used. PCR testing at 60 and 90 days after treatment have been recommended to document clearance. Many patients will show improvement within 24-72 hours. Some patients will develop a subclinical infection that may resurface if immunosuppressed or undergo splenectomy. Immunosuppressant therapy is not advised.
In this case, B coco was discovered. This organism has been associated with immunocompromised patients or those with a splenectomy. The poodle had splenectomy performed years ago due to complications associated with gastric dilatation-volvulus. The patient was treated with imidocarb and responded favorably.
As the incidence of vector-borne disease increases around the Unites States, the consideration of these organisms as a cause for disease also increases.
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