Trichomoniasis is caused by a sexually transmittable parasite Trichomonis vaginalis and presents as acute vaginitis. The protozoa are transmitted through genital-genital contact. Infected men act as carriers and have few symptoms. Symptoms (if they occur) are seen 4-28 days after becoming infected. The organism lives in the reproductive and urinary tracts of men and women. It can cause inflammation of these areas and eventually result in infertility.

There is limited evidence for transmission of the organism through bodies of water such as hot tubs or via fomites.