A case of Chagas disease in a puppy adopted from the southern United States

Rebecca Egan

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2022;26(4):23.

Shortly after arriving from Texas for adoption in Ontario, a six-month-old Dachshund mix puppy was presented to a veterinarian with a 1-day history of anorexia accompanied by lethargy, soft stools, and straining to defecate.  Clinical signs did not resolve with symptomatic treatment, and the puppy went on to develop hypothermia, hypoglycemia and poor oxygenation.  Stabilization was attempted, but the puppy died due to cardiopulmonary arrest.  The puppy was presented to the AHL for postmortem examination which identified 150 mL of thoracic effusion, a lesser amount of pericardial effusion, and extensive pale mottling of the heart that was visible from the epicardial surface.  Auricles appeared symmetrical and of normal size.  On cut section, the right ventricular free wall was thickened to 4 mm and the LV:RV thickness ratio was 2:1 (Fig. 1A).  The myocardium was pale, and there were no grossly visible structural defects.  Other notable findings included pulmonary congestion and edema, 150 mL of serous abdominal effusion with edema expanding intra-abdominal adipose and connective tissues, and accumulation of ample hemorrhagic contents throughout the jejunum.  Microscopic examination revealed severe pancarditis characterized by widespread infiltration of neutrophils, eosinophils and mononuclear cells occupying greater than 50% of the tissue sections (Fig. 1B).  Multifocally, individual myofibers contained variably sized, intracytoplasmic oval to elongate pseudocysts measuring approximately 150 um x 50 um that harboured numerous 2-4 um round to oval protozoal amastigotes (Fig. 1C).  The inflammatory infiltrate separated and sometimes obscured cardiomyocytes that exhibited occasional necrosis.  A heart sample was submitted for PCR testing which confirmed the presence of Trypanosoma cruzi organisms.

Trypanosoma cruzi is a zoonotic pathogen that can infect many mammals, and is known for causing Chagas disease (also known as American trypanosomiasis) in dogs and humans.  The parasite is endemic in parts of South America, Mexico, Central America, with presence also documented in the southern United States, and is transmitted by a biting fly vector or though ingestion of infected bugs or contaminated feces.  Chagas disease can manifest with acute and/or chronic phases, and the incubation period can range from approximately 5 to 42 days.  In addition to non-specific febrile illness, acutely affected dogs can present with anorexia, lethargy, vomiting, diarrhea, lymphadenopathy, hepatomegaly, and/or splenomegaly and reports of acute clinical myocarditis seem to be less common.  This case highlights the importance of obtaining travel history as part of a clinical work-up, since animals travelling between different geographical locations can carry pathogens not native to the area in which they reside.   AHL

Figure 1. Gross and histologic lesions of T. cruzi in a puppy.  A. Cross-section of the heart showing thickening of the right ventricular free wall and pallor of the myocardium.  B. Microscopic section of heart demonstrating widespread inflammatory infiltrates throughout the wall (>) (H&E, 4x).  C. Microscopic section of heart capturing predominately neutrophilic inflammation surrounding a cardiomyocyte harbouring an intracytoplasmic pseudocyst containing numerous 2-4 um protozoal amastigotes (*) (H&E, 40x).

References

1. Wilkowsky S. Trypanosomiasis in Animals. The Merck Veterinary Manual. Mar 2020. [cited 2022 November 15].  Available from: https://www.merckvetmanual.com/circulatory-system/blood-parasites/trypanosomiasis-in-animals .

2. Robinson W, Robinson N. Cardiovascular System. In: Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, 6th ed. Maxie MG, ed. Elsevier, 2016;vol 1:44.