Fatal infection with emerging apicomplexan parasite Hepatozoon silvestris in a domestic cat

Background: Hepatozoon silvestris is an emerging apicomplexan parasite discovered in European wild cats from Bosnia and Herzegovina and blood samples of a domestic cat from Southern Italy in 2017. It has also been identified in Ixodes ricinus collected from a domestic cat in Wales, UK, in 2018. The clinical relevance, pathogenesis and epidemiology of this novel Hepatozoon species are not yet understood. Thus, the objective of this paper was to report and describe the first fatal case of an H. silvestris infection in a domestic cat. Results: The cat, which originated from Switzerland, died shortly after presenting clinical signs of lethargy, weakness and anorexia. At necropsy, no specific lesions were observed. Histopathology of the heart revealed a severe lympho-plasmacytic and histiocytic myocarditis. Mature and developing protozoal meronts morphologically compatible with Hepatozoon species were observed associated with the myocardial inflammation. No other lesions were present in any other organ evaluated, and the cat tested negative for retroviral and other immunosuppressive infectious agents. Polymerase chain reaction from the myocardium resulted in a specific amplicon of the Hepatozoon 18S rRNA gene. Sequencing and BLAST analysis revealed 100% sequence identity with H. silvestris. Conclusions: The severity of the infection with fatal outcome in an otherwise healthy animal suggests a high virulence of H. silvestris for domestic cats. The presence of this emerging parasite in a domestic cat in Switzerland with no travel history provides further evidence for a geographical distribution throughout Europe.