Pancarditis as the sole clinical manifestation of protothecosis in a Boxer dog

A 4.2-year-old, male castrated Boxer was diagnosed with a dilated cardiomyopathy phenotype, complex arrhythmias and left-sided congestive heart failure, but died suddenly shortly after initial diagnostics were complete. Ultrasensitive cardiac troponin I was markedly elevated (9.345 ng/mL [reference range: 0-0.06 ng/mL]), and a Trypanosoma cruzi immunofluorescent antibody titer was positive at 1:80. Necropsy revealed a severe, necrotizing, histiocytic, lymphoplasmacytic pancarditis with intralesional algae consistent with protothecosis, as well as evidence of left-sided congestive heart failure. Algal organisms were found only in the heart. Acute Chagas disease was not thought to play a role given the lack of T. cruzi amastigotes on postmortem and negative reverse transcription polymerase chain reaction testing on formalin fixed, paraffin embedded myocardium, however a possible contribution of chronic Chagas disease to the clinical picture could not be ruled out. Canine protothecosis is typically a disseminated disease. This case represents the first report of canine protothecosis limited solely to the heart.