Chagas´ disease is an endemy caused by the protozoa Trypanosoma cruzi, which is spread from southern United States to Argentina. According to data from the World Health Organization, up to 20 million people may be infected in South America, thus making this disease a very important public health problem. This disease occurs naturally in several animal species, despite data still lacks about natural infection in dogs. Thus, this work aimed to characterize Chagas´ disease of natural occurrence in three adult dogs from Western Brazil.

Animals were referred to the Cardiology Service of the Veterinary Teaching Hospital of São Paulo State University (Unesp), Campus of Jaboticabal, Brazil, where they were evaluated. After serologic testing by indirect immunofluorescence for Trypanosoma cruzi, dogs were considered positive to such disease, owing to the high positive titles: 1:2560, 1:1280 and 1:320. Moreover, it was also performed a serologic test to differentiate from Leishmaniasis, which was negative for all dogs.

Physical examination showed no alterations, as well as blood and serum biochemical profiles. However, electrocardiographic examination showed respiratory sinus arrhythmia, sinus arrest and enlargement of QRS complex in one of the dogs. In the remaining, it was only observed sinus rhythm. Average values of systolic, mean and diastolic arterial pressures from the three dogs were 129, 99 and 82 mmHg, respectively, which were within the normal range for canine species. Ecodopplercardiography showed right atrioventricular enlargement, thickening of the interventricular septum and thickening of the left ventricle free wall in all animals. It was also determined a mild abnormal ventricular relaxation in all dogs.

Therefore, the high antibody titles against T. cruzi, associated to the alterations in electrocardiography and echocardiography are considered indicative of a chronic chagasic infection in these animals. As dogs are considered reservoirs of this disease and can contribute to the increase in the risk of spreading the disease to humans, the clinician should be aware and consider this as a possible differential diagnosis of cardiac diseases in dogs from South American countries.