The disease is caused by urogenital (vaginal) Trichomonas vaginalis - a one-celled microorganism belonging to the simplest class of flagellates, has a length of 13-18 mm (30-40 mm). Thanks to the flagella and undulating movements (undulating) membrane Trichomonas can be actively moved, and the high plasticity of the body allows it to form pseudopodia and to penetrate into the intercellular spaces.
Urogenital trichomonas is a parasite of man, adapted to live only in the urogenital organs. In other organs (intestines, stomach, etc.) and outside the human body, they quickly die because they do not form a protective devices and are unstable to adverse environmental factors. Particularly detrimental effect on them, drying, heating above 45 ° C, direct sunlight, changes in osmotic pressure. Therefore, to detect urogenital trichomonads in the external environment, such as in open water even in areas where the greatest concentrations of people in the wastewater, and public baths, etc. is not possible. In vivo urogenital trichomonads do not cause diseases in animals, which parasitize other types of Trichomonas.