Laboratory tests for diagnosing and monitoring canine leishmaniasis

Despite several reviews on canine leishmaniasis, none throughly described clinico-pathological abnormalities and their clinical usefulness. The aim of this review is to provide information concerning current diagnostic tests that may be relevant for clinical pathologists, from a practical perspective. In canine leishmaniasis, the CBC reveals non-regenerative normocytic normochromic anemia. Thrombocytopenia or leukogram changes may be observed. Clinical chemistry and urinalysis may evidence renal dysfunction (azotemia, decreased urine specific gravity, proteinuria) and inflammatory/immune activation (increased acute phase proteins or 2- and/or -globulins). The gammopathy is polyclonal but it can be oligo- or monoclonal, especially in dogs co-infected by other vector-borne pathogens. When lesions are accessible to fine needle aspiration (lymhpoadenomegaly, nodular lesions, joint swelling), cytology is strongly advised. The disease is confirmed if Leishmania amastigotes are identified along with pyogranulmatous inflammation or lymphoplasmocytic hyperplasia. If results are inconclusive, the parasite should be identified by histology/immunohistochemistry or PCR on surgical biopsies. Alternatively, cytology and PCR may be performed on bone marrow, where amastigotes, erythroid hypoplasia/myeloid hyperplasia, plasmocytosis, or secondary dysmyelopoiesis can be observed. Dogs with overt disease generally have high antibody titers. Low titers may be found in immunologically resistant infected dogs, or in exposed dogs (dogs receiving contacts from, but not confirmed as harboring the parasite). In dogs with strong clinical suspicion of leishmaniasis, quantitative serology is recommended as it can be conclusive for diagnosis when high-titer antibodies are detected but not when antibody titers are low. In treated dogs, renal function and the inflammatory/immune reaction should be periodically monitored.