A rapid motility observed in freshly collected feces is most suggestive of infection with which protozoan?

• A. Toxoplasma
• B. Tritrichomonas
• C. Mycoplasma
• D. Ehrlichia canis

Answer: (B)

Rapid motility in a fresh fecal sample points to a flagellated protozoan, because the moving trophozoite stage with multiple flagella is observed as vigorous movement on direct smear. Tritrichomonas species are classic examples of this, with slender, pear-shaped trophozoites that whip around due to their flagella, making rapid movement a key clue in fresh feces. Toxoplasma gondii, while a protozoan, forms oocysts that are shed in feces but are not actively motile in the sample, and diagnosis relies on serology or molecular tests rather than observing rapid movement. Mycoplasma and Ehrlichia canis are bacteria and do not appear as motile protozoa in feces. So the rapid, flagellated movement best points to Tritrichomonas.