Retrospective study of canine infectious haemolytic anaemia cases reveals the importance of molecular investigation in accurate postmortal diagnostic protocols

Abstract Infectious haemolytic anaemia (IHA) in dogs share similar clinical signs including fever, lethargy, icterus, paleness of mucous membranes and splenomegaly. Postmortal findings are similar and, without additional diagnostic methods, an accurate aetiological diagnosis is difficult to achieve. In order to investigate causes of lethal IHA in Croatian dogs, we performed a retrospective study on archived formalin-fixed, paraffin-embedded tissue blocks (FFPEB) from dogs that died due to haemolytic crisis, using microscopic and molecular diagnostic tools to determine the aetiological cause of disease. Molecular analysis was performed on kidney, lung, myocardium and spleen on FFPEB from all dogs. The originally stated aetiological diagnosis of B. canis or leptospirosis was confirmed in only 53% of the dogs. PCR and sequencing revealed that, in addition to the expected pathogens, B. canis and Leptospira interrogans , the presence of previously undiagnosed “new” pathogens causing anaemia including Candidatus Neoehrlichia mikurensis and Anaplasma phagocytophilum . Furthermore, Theileria capreoli was detected for the first time in a dog with postmortal descriptions of lesions. Intensive extravascular hemolysis was noticeable as jaundice of the mucosa, subcutis and fat tissue, green or yellow discoloration of renal parenchyma caused by bilirubin excretion in the renal tubules and bile accumulation within the liver in 90% of the dogs. This work highlights the value of molecular diagnostics to complement traditional ante-mortem and post-mortem diagnostic protocols for the aetiological diagnosis of pathogens associated with IHA.