Trichomoniasis is neither a virus nor a bacterium. It is caused by a parasite, specifically a single-celled organism called Trichomonas vaginalis. This parasite belongs to a group known as protozoa, which are microscopic organisms more complex than bacteria but still made up of just one cell. The distinction matters because it affects how the infection behaves in your body, how it’s detected, and how it’s treated.
Why It’s a Parasite, Not a Virus or Bacterium
Trichomonas vaginalis is a protozoan, the most common disease-causing protozoan in humans in industrialized countries. Unlike bacteria, which are simple cells without a defined nucleus, this parasite has a large, structured nucleus packed with genetic material. And unlike viruses, which are essentially packets of genetic code that hijack your cells to reproduce, T. vaginalis is a fully independent living organism that moves on its own and divides on its own.
Under a microscope, the parasite is pear-shaped and measures roughly 7 to 30 micrometers long. It has five whip-like tails called flagella that it uses to swim through the genital tract. It reproduces by splitting itself in two, a process called binary fission. This self-sufficiency is what separates protozoa from viruses, which cannot replicate without a host cell.
This classification also explains why standard antibiotics designed for bacterial infections won’t work against trichomoniasis. Antiparasitic medications are required instead. The infection is curable with the right prescription, which is a key difference from viral STIs like herpes or HIV that remain in the body long-term.
How Common Trichomoniasis Is
Trichomoniasis is the most prevalent nonviral sexually transmitted infection worldwide. The CDC estimates there were more than two million infections in the United States in 2018, and roughly 2.6 million people are affected at any given time. Despite those numbers, most people have never heard of it, partly because the infection often produces no symptoms at all.
How It Spreads
The parasite spreads through sexual contact. In women, it takes up residence in the lower genital tract. In men, it lives in the urethra and prostate. Because many carriers have no symptoms, the infection passes easily between partners who don’t realize they’re infected. Condoms reduce transmission risk, though they don’t eliminate it entirely since the parasite can be present on skin not covered by a condom.
Symptoms in Women and Men
When symptoms do appear, they differ between sexes. Women are more likely to develop noticeable signs: an unusual vaginal discharge that may be yellow-green or frothy, a strong odor, itching or irritation around the genitals, and discomfort during urination or sex. The cervix can develop small red spots, sometimes described as a “strawberry cervix,” though this is typically only visible during a medical exam.
Men are far more likely to carry the infection without knowing it. When symptoms show up, they usually involve mild irritation inside the penis, a thin discharge, or slight burning after urination or ejaculation. Because these symptoms are subtle and often resolve on their own (even though the infection remains), men frequently go undiagnosed and unknowingly pass the parasite to partners.
Health Risks Beyond Discomfort
Trichomoniasis is more than a nuisance infection. Left untreated, it creates inflammation in the genital tract that makes you significantly more vulnerable to other infections. People with trichomoniasis have a 1.5 times increased risk of acquiring HIV, according to the World Health Organization. The inflammation damages the protective lining of the genital tract, creating easier entry points for the virus.
During pregnancy, the stakes rise further. Trichomoniasis has been linked to premature rupture of membranes, preterm delivery, and low birth weight. Identifying and treating the infection during pregnancy can reduce these risks.
How It’s Diagnosed
Because trichomoniasis is a parasite rather than a virus or bacterium, it requires specific tests. The older method, called a wet mount, involves placing a sample of vaginal fluid on a slide and looking for the moving parasites under a microscope. This method is quick but misses a significant number of infections because the parasites die quickly once outside the body.
Newer molecular tests that detect the parasite’s genetic material are far more accurate and are now the preferred approach. These can be run on vaginal swabs or urine samples. For men, urine-based testing is the most practical option since the parasite can be difficult to detect through other methods.
Treatment and Cure
Because trichomoniasis is caused by a parasite rather than a virus, it is completely curable. Treatment involves antiparasitic medication taken by mouth, typically as either a single dose or a week-long course depending on the situation. Both partners need treatment at the same time, even if one has no symptoms, to prevent reinfection. You should avoid alcohol during treatment and for a period afterward, as the medication can cause a severe reaction when combined with alcohol.
Reinfection is common. About one in five people get trichomoniasis again within three months of treatment, usually because a partner wasn’t treated simultaneously. A follow-up test two weeks to three months after treatment confirms the infection is gone.