October 2015

Beagle puppy

A 9-week old Beagle puppy from Oklahoma near the Texas border was presented with syncope, labored breathing, and ascites. Electrocardiogram revealed prominent conduction abnormalities. The pup was euthanitized due to cardiac decompensation. A Giemsa stained blood smear was prepared prior to euthanasia. The organisms below were observed by microscopy (100X objective).

What is your diagnosis?

Answer

These are trypomastigotes of Trypanosoma cruzi, causative agent of Chagas Disease, or American Canine Trypanosomiasis. Trypanosoma cruzi is endemic in parts of Texas, and is transmitted by triatomine bugs (commonly called "kissing" or "assassin bugs") via the stercorarian route. Metacyclic trypomastigotes deposited by infected triatomines invade cells near the bite site or of intact mucosa and rapidly transform into amastigotes, which undergo repeated rounds of asexual reproduction. Trans-placental transmission of the parasite is also documented. Trypanosoma cruzi disseminates in the vertebrate host, and damage is particularly pronounced in cardiac tissue in acute and chronic canine Chagas infections.