Overview

• Caused by the zoonotic hemoflagellate protozoan parasite Trypanosoma cruzi.
• Infection-transmission occurs after infected feces of a vector (Triatominae) are deposited in a wound (bite site of vector) or mucous membrane, dog eats an infected vector,or by contaminated blood transfusion.
• After local multiplication at entry site (5 days post-infection), hematogenous spread occurs to most organs but mainly the heart and brain.
• Organisms become intracellular, multiply, then rupture out into circulation to produce maximal parasitemias, associated particularly with acute myocarditis and less commonly with diffuse encephalitis (14 days post-infection).
• Parasitemias wane (subpatent 30 days post-infection).
• Antibody titers rise (detectable by 16 days post-infection).
• Dog enters a protracted asymptomatic period (can last for months to years); progressive and insidious development of myocardial degeneration; eventual dilative cardiomyopathy.
• South and Central America-endemic (in both humans and pets).
• United States-mostly in Texas but other southern states also, where infected vectors and reservoir hosts live, with raccoons, opossums, and armadillos the main reservoirs in the southeast and mice, rats, and squirrel species in the southwest.

Signalment

• Young dogs-most common
• Acute-dogs usually <2 years
• Chronic-old dogs
• Hunting breeds-likely to contact vectors or reservoir hosts
• More often males
• Cats-no cases reported in North America.

Signs

Causes & Risk Factors

T. cruzi

Differential Diagnosis

• Cardiomyopathy
• Congenital cardiac defects
• Traumatic myocarditis
• Distemper
• Toxoplasmosis
• Neosporosis

CBC/Biochemistry/Urinalysis

Generally normal

Other Laboratory Tests

• Serology-positive titer confirms diagnosis available from the CDC's parasitology unit.
• On-site immunochromatographic antibody tests have high sensitivity and specificity when used in dogs-excellent tool for survey work not only in dogs but also wildlife.
• Antibody titers very sensitive and specific but most cross-react with Leishmania.
• Organism isolation-LIT culture; collect 50 mL heparinized blood.
• Examination above the buffy coat in a microhematocrit tube (spun down to read PCV) using 40× microscope objective-organisms during period of high parasitemia.
• PCR-very useful during indeterminate and chronic stages when blood trypomastigotes are very difficult to demonstrate. Has high specificity but low sensitivity unless samples from multiple tissues are examined. Not yet commercially available.
• Elevated troponin I-acute disease.

Imaging

• Radiography-acute: cardiomegaly, pulmonary edema, and (rarely) mild pleural effusion; chronic: cardiomegaly.
• Echocardiography-acute: rarely shows chamber or wall abnormalities; chronic: reduced ejection fraction, fractional shortening, and thinning of right and left ventricular free wall.

Diagnostic Procedures

Client Education

• Alert owner to possible zoonotic risk and potential for sudden death.
• Acute-usually develops into the chronic form, which is often fatal.
• Infected intact female-can transfer infection to offspring.

Drug(s)

• Several drugs have limited efficacy during the acute stage; none produces a clinical cure; even treated animals may progress to chronic disease.
• Benzimidazole (Ragonil) 5 mg/kg PO q12h for 60 days; preferred drug for use in dogs; markedly improves acute disease in humans and probably dogs also. Available from CDC.
• Cythioate (Proban)-3.3 mg/kg PO q48h; effective in reducing vector populations; Fipronil Spot-on (Frontline Top Spot, Merial) has been shown to be ineffective in preventing reduviidae from feeding on dogs.
• Supportive treatment of dilated cardiomyopathy (right and left cardiac failure) and ventricular arrhythmias.

Zoonotic Potential

Exists; essentially incurable in humans, thus euthanasia of infected dogs is an option.

Abbreviations

• CNS = central nervous system
• LIT = liver infusion tryptose
• PCR = polymerase chain reaction
• PCV = packed cell volume
• VPC = ventricular premature complex