Occurrence, Risk Factors, and Molecular Characterization of Ehrlichia canis Infection in Clinically Suspected Dogs from a Tropical Region of South India

Canine monocytic ehrlichiosis, caused by Ehrlichia canis, is an important tick-borne disease of dogs in tropical and subtropical regions. This cross-sectional study investigated the occurrence, associated risk factors, and molecular confirmation of E. canis infection among clinically suspected dogs in Andhra Pradesh, India, and evaluated the diagnostic performance of blood smear microscopy relative to PCR. Peripheral blood samples were collected from 442 clinically suspected dogs presented to 90 veterinary dispensaries across the state. Dogs were selected based on clinical features suggestive of ehrlichiosis, including inappetence, pale mucous membranes, tick infestation, fever, lymphadenopathy, weakness, and hemorrhagic signs. Samples were examined by Giemsa-stained blood smear microscopy and subsequently tested by PCR. Representative virB9 gene amplicons were sequenced and compared with reference sequences available in GenBank. Microscopy detected E. canis in 37/442 dogs (8.37%), whereas PCR detected infection in 51/442 dogs (11.54%). Logistic regression analysis indicated that female dogs, mongrels, kennel dogs, and dogs with tick infestation had significantly higher odds of infection, while dogs with a history of tick-control measures had lower odds. Sequence comparison and phylogenetic placement based on the partial virB9 fragment supported molecular confirmation of the detected E. canis isolates and showed similarity with previously reported Indian and international isolates. These findings provide regional evidence on the occurrence and epidemiology of canine ehrlichiosis in clinically suspected dogs and support PCR as a more reliable confirmatory method than microscopy.