Trichomonas (“Trich”) is a protozoan parasite transmitted by sex. Women experience vaginal discharge and itching, men may feel some discomfort urinating, but the vast majority have no symptoms. Women can get the disease from sex with either men or women; men likely only get it from sex with women.
Symptoms begin 1 to 4 weeks after infection in half of people, but as with all STDs, the germ can linger for a while before acting up, so a person can’t be sure who transmitted it to them. It can be diagnosed with 100% certainty if the parasites themselves can be seen flitting around under the microscope (they’re visible in 50% of cases). If none are noticed, a rapid swab test can be performed that takes 10 minutes but may miss 10% to 15% of cases. The best test has to be sent out to a regular lab and takes a day or more for results.
The diagnosis is rarely made among men, who rarely have symptoms. Men with painful urination get treated for other germs first; if they still don’t get better, testing or simply treating for Trich may be tried. See Urinary Problems in Men.
Without treatment, the parasite may go away on its own in several months. There are some rare complications if the parasite spreads to other genital organs, and some dangers during pregnancy, but usually not. Trichomonas may make it easier for women to acquire HIV if exposed. It has been shown that screening for it in people without symptoms isn’t useful. Sexual partners should be treated without testing, to avoid having ongoing back and forth transmission (which medically we call “ping-pong: I get it, you get it, I get it again , you… etc.).
See also Vaginal Discharge.