Clinically, the acute form is characterized by lymphadenomegaly. Acute myocarditis is not uncommon. Common signs include pale mucous membranes, a slowed capillary refill time, weak pulse, tachyarrhythmia, and terminal hypothermia and respiratory distress. Dogs that do not die develop ascites and hepatomegaly due to right side heart failure. Anorexia and diarrhea are also common.
Neurologic signs including weakness and ataxia, suggesting distemper, are also common.
ECG changes during the acute phase are variable. During the asymptomatic period between the acute and chronic phase of infection, ECG may be normal except for intermittent ventricular arrhythmia, often exacerbated by exercise. Sudden death can occur due to fatal cardiac arrhythmia. Trypanosomiasis should be considered in any dog with signs of myocarditis or cardiomyopathy. Felines are reported to be susceptible to infection but little is known of clinical disease in this species.