Case #496 – July, 2019

A 29-year-old female working at a zoo as a primate intern developed gastrointestinal symptoms including diarrhea and cramping. She sought medical attention from her health care provider which included a stool examination for ova and parasites (O & P). Figures A–C show what was observed in a wet-mount preparation from a formalin-ethyl acetate concentration procedure. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

This was a case of balantidiasis caused by the ciliated protozoan, Balantidium coli. Swine are the primary hosts; humans, nonhuman primates, and rodents can also serve as reservoir hosts.

Diagnostic morphologic features shown in the images were:

large trophozoites with cilia within the size range for B. coli (40-200 micrometers)
presence of a cytostome (located at the tapered end)

More on balantidiasis: https://www.cdc.gov/dpdx/balantidiasis/index.html

Images presented in the dpdx case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.

DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.

Page last reviewed: August 28, 2019

Content source: Global Health, Division of Parasitic Diseases and Malaria