In clinical practice, this is the most common. Nearly half the patients who complain of pruritus[itching] vulvae harbour this organism. It is almost entirely a disease of the childbearing era, though young girls and postmenopausal women are not at all immune. There is no doubt that this infection is sexually transmissible but, in some instances, it can be acquired by inadequate hygiene or the use of an infected person’s towels, bath or clothes. Its ingress to the vagina is favoured by a low general resistance and when the pH is raised as during a menstrual period [pH 5-6]. It is not uncommon during pregnancy and is often associated with gonococcal infection.
The trichomonas organism is a protozoan, actively motile, slightly larger than a leucocyte and is anaerobic. Three types of trichomonas are known, namely, Tr. Buccalis, which is a normal inhabitant of the mouth. Tr. homonis, a normal inhabitant of the anal canal and rectum; and Tr. Vaginalis is found in the vagina. It has been shown by transplantation experiments that Tr. Buccalis and Tr. Homonis are unable to survive in the human vagina. Men may harbour Tr. Vaginalis in the urethra and prostate. A trichomonad has four anterior flagella, and they move along the mucous membrane.