December 2023 – Cardiovascular and Infectious Diseases

A 30-year-old immunocompromised woman living in the northeastern United States was found unresponsive by her boyfriend. She had never traveled outside of the area and worked as a retail clerk Autopsy reveals the following microscopic findings (see figures).

Figure 1: 4x
Figure 2: 40x oil
Figure 3: 100x

What is the organism?

  • Trichinella spiralis
  • Trypanosoma cruzi
  • Toxoplasma gondii
  • Sarcocystis hominis

The correct answer is ...

Toxoplasma gondii.

All four of the following organisms can involve myocardium but can be distinguished based on morphology. 

Trichinella spiralis larvae are able to be distinguished on low-power microscopic examination, but distinction between ToxoplasmaTrypanosoma, and Sarcocystis requires high-power examination under oil. 

Sarcocystis hominis have a more tubular appearance, and Trypanosoma cruzi amastigotes are remarkable for the presence of kinetoplasts, a rod-shaped structure situated close to the nucleus.

Toxoplasma gondii can be seen in the form of encysted bradyzoites as well as individual tachyzoites. This case is an example of a single cyst within myocardium, containing organisms morphologically consistent with Toxoplasma gondii.


  1. Hidron A, Vogenthaler N, Santos-Preciado JI, Rodriguez-Morales AJ, Franco-Paredes C, Rassi A Jr. Cardiac involvement with parasitic infections. Clin Microbiol Rev. 2010 Apr;23(2):324-49. doi:10.1128/CMR.00054-09. PMID: 20375355; PMCID: PMC2863361.
  2. Mishra A, Ete T, Fanai V, Malviya A. A review on cardiac manifestation of parasitic infection. Trop Parasitol. 2023 Jan-Jun;13(1):8-15. doi:10.4103/tp.tp_45_21. Epub 2023 May 19. PMID: 37415759; PMCID: PMC10321584.

Michael Kritselis, D.O.

Fellow, Cardiovascular Pathology
Mayo Clinic

Melanie Bois, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Associate Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.