Occult Co-infection with Ehrlichia canis and Hepatozoon canis in a Dog Diagnosed by Real-Time PCR: A Sentinel Case from a One Health Perspective

Tick-borne co-infections can be difficult to recognise when clinical and routine laboratory findings are non-specific. This case report describes molecular detection of concurrent Ehrlichia canis and Hepatozoon canis infection in a two-year-old female Labrador Retriever presented for a health check after a previous episode of tick fever. The dog weighed 28 kg and had a rectal temperature of 103.8 °F, pale mucous membranes and no visible ticks at presentation. Haematology indicated mild microcytic anaemia, while leukocyte and platelet counts were within reference intervals. Biochemistry showed hyperproteinaemia, hypoalbuminaemia and hyperglobulinaemia, with an albumin-to-globulin ratio of 0.36. Real-time polymerase chain reaction (PCR) detected E. canis (cycle threshold [Ct] 29.81) and H. canis (Ct 31.66); the Babesia canis complex and B. gibsoni were not detected. Treatment comprised doxycycline at 10 mg/kg orally once daily for 28 days, supportive care and a single oral dose of fluralaner for tick control. Repeat PCR testing at the reported follow-up was negative for both detected pathogens. Because doxycycline has no dependable activity against H. canis, the negative follow-up result cannot establish parasite elimination and warrants further monitoring. This case illustrates the diagnostic value of multi-pathogen PCR when routine findings are inconclusive and the potential relevance of veterinary case detection to One Health surveillance.