Infestation by a flagellate protozoan. This parasite has a world-wide distribution and women aged between 30 and 50 are the group mostly affected. Three kinds of trichomoniasis occur in humans, but only can cause symptoms. Most people who are infested are not troubled by the parasite and are carriers. Symptoms arise when the numbers of parasites in the vagina have risen to such an extent that the vaginal wall is damaged. Inflammation sets in and this forms a good breeding ground for a variety of bacteria. A yellowish-green discharge from the vagina, with itching and pain, are the consequence. These symptoms often recur after every menstruation. Pregnant women are particularly susceptible to trichomoniasis. The symptoms can last for months but their intensity declines with time. Men are much less frequently affected than women. Inflammation of the urethra and prostate can occur, with resultant pain, itching, problems with urination, and discharge from the penis. The infestation can be transmitted by sexual contact. Towels and the like which are contaminated with Trichomonas can also lead to infestation, because the parasite can remain alive for as much as 24 hours when outside the body.