Diagnóstico patológico e molecular da infecção por Ehrlichia canis em caninos de Minas Gerais

Abstract

Canine monocytic erliquiosis (CME) is an infectious disease caused by the bacterium Ehrlichia canis, with clinical signs related to bone marrow aplasia and thrombocytopenia. Necropsy lesions are nonspecific and disseminated hemorrhages, splenomegaly, hepatomegaly and lymphoadenomegaly may occur. The microscopic findings depends on the clinical phase of the disease, but often occur multifocal hemorrhages, perivascular lymphoplasmocytary infiltration and vasculitis in various tissues, spleen with white pulp hyperplasia, interstitial pneumonia, membranous glomerulonephritis and bone marrow aplasia. The diagnosis is based on clinical manifestations, necropsy lesions and the ricketsian inclusions in the cytoplasm of monocytes and lymphocytes, which are rare and visualized only in the acute phase of the disease. Thus, the aim of this study was to describe the main lesions observed in CME, validate a tissue PCR for the molecular diagnosis of canine erlichiosis and identify the circulating E. canis strain in dogs in southern of Minas Gerais, Brazil. Tissues from 40 canines referred for necropsy in the Veterinary Pathology Sector of UFLA were submitted to histopathology and Nested-PCR avaliation. Of these, 28 had compatible lesions and positive PCR for CME and 12 animals diagnosed with other diseases were negative in PCR for EMC (negative control). In the PCR performed on spleen and kidney samples, 14 dogs (50%) were positive in both organs, 16 (57,1%) positive in the spleen and 26 canines (92.8%) positive in the kidney. The CME most frequent macroscopic lesions were edema and generalized hemorrhages, anemia and jaundice, lesions of chronic renal failure (uremia), lymphadenomegaly, splenomegaly and hepatomegaly. Microscopically hemorrhages and multifocal thrombosis, severe hemosiderosis in the spleen, lymph node and bone marrow, bone marrow aplasia, interstitial lymphoplasmocyte nephritis, membranous glomerulonephrite and severe congestion with atrophy of hepatocytes were the most important findings. Fibrinoid necrosis and vasculitis were observed in five animals (17.8%). The sequence obtained from E. canis when compared with the sequences of fragments of genes available in GenkBank, obtained 95.9% identity with the E. canis strain Jake (NC_007354.1) and 95.6% with the Oklahoma strain (NR_118741.1). The nested PCR associated with the lesions was effective for the diagnosis of CME.