Enhancement of chronic Trypanosoma cruzi myocarditis in dogs treated with low doses of cyclophosphamide.

An enhancement of chronic myocarditis was obtained in dogs chronically infected with Trypanosoma cruzi protozoa soon after they were submitted to treatment with low doses of cyclophosphamide (50 mg/sq m bs three times a week for 3 weeks). Such treatment did not cause immunodepression. Myocarditis varied in intensity, but was quite severe and diffuse in some animals, with focal fibrinoid, coagulative, and lytic necrosis and invasion of disintegrating myocardial fibers by the mononuclear inflammatory cells. Untreated infected controls exhibited mild focal myocarditis, usually represented by accumulation of lymphocytes in the interstitial connective tissue. It is suggested that the administration of low doses of cyclophosphamide interfered with the immunologic suppressor network that is thought to maintain the chronic indeterminate (or latent) phase of T cruzi infection.