Circulating and bone marrow myeloid cells containingamastigotes in a case of advanced canine leishmaniosis.

Abstract

A 5-y-old male Poodle mix was presented with intermittent vomiting, anorexia, and weight loss. Physical examination revealed emaciation, lethargy, dehydration, hypothermia, respiratory distress, and splenomegaly. Based on clinicopathologic, serologic, and parasitologic findings, diagnoses of severe leishmaniosis and dirofilariasis were made. Extracellular, intraneutrophilic, and intramonocyticamastigotes were observed on blood smear and buffy coat smear examination. In blood smears, 0.2% of neutrophils were observed to be infected; in buffy coat smears, 0.5% of neutrophils and 0.1% of monocytes were found to be infected.amastigotes were also found engulfed by eosinophils and neutrophil precursors in bone marrow aspiration cytology. The detection ofamastigotes in blood smears is rare, and the clinical significance is uncertain. In circulating blood,amastigotes are primarily found phagocytized by neutrophils. Although debatable, there is growing evidence that neutrophils are used as carriers enabling the "silent entry" of the protozoa into macrophages ("Trojan horse" theory). To date, cytologic screening of blood smears for the diagnosis of canine leishmaniosis is not a routine practice. Clinical pathologists and practitioners should be aware thatamastigotes may be present in neutrophils and less frequently monocytes during blood smear evaluation; neutrophil precursors and eosinophils may also be parasitized in bone marrow specimens.