STD Awareness: Trichomoniasis, the Pear-Shaped, Blood-Sucking, Silent Scourge

What’s shaped like a pear, hangs with a posse of bacteria, and is a silent scourge upon millions of urogenital tracts? I hope you guessed Trichomonas vaginalis, the single-celled parasite that causes trichomoniasis, or trich (pronounced “trick”). Trich is the most common curable sexually transmitted disease out there — currently afflicting around 3.7 million Americans and 156 million Earthlings.


These single-celled creatures pack a punch, but the body fights back.


When trich causes symptoms, sufferers might experience vaginal discharge (which sometimes has a bad odor), penile burning or discharge, spotting, and itching or swelling in the genital area. But around 70 percent of infections have no symptoms at all, making it a mostly “silent” disease. Based on the totality of the evidence, the Centers for Disease Control and Prevention (CDC) doesn’t currently recommend routine screening for trich in people without symptoms.

But it’s the subject of some debate. Since both symptoms and screenings are rare, and the disease isn’t reportable, some health experts worry that trich could be doing a lot of damage right under our noses. An infection during pregnancy could increase risk for preterm labor or low birth weight. It can increase risk for both acquiring and transmitting HIV from or to a partner. Women with trich are more likely to acquire an HIV infection when sexually exposed to the virus — in fact, one study estimated that 6.2 percent of all HIV infections among U.S. women could be attributed to trich. It’s also easier to catch HIV from a man with trich than from a man without trich.

Trichomonads: Tiny and Tricky

A trichomonad flattens itself over a vaginal cell, maximizing surface area between parasite and host.

Trichomonads are individual members of the species T. vaginalis. Despite only having a single cell to work with, they’re pretty good at causing an abundance of trouble for us humans. Once it lands in a vagina or a urethra, a trichomonad propels its pear-shaped body with little “tails” called flagella. Its first mission is to stake claim on a piece of host tissue — vaginal, cervical, or urethral cells. Once it finds a nice plot of land, it stretches its body across a cell surface and and sinks some if its appendages inside, oozing an enzyme that helps it eat away at our delicious tissues. Its voracious appetite doesn’t stop there. Trichomonads slurp up red blood cells, which are rich in fat and iron, and can poison certain immune cells — and might be eating them, too. One of its favorite meals might be lactobacilli, “good” bacteria associated with vaginal health — and, by feasting upon bacterial passersby, it’s disrupting the local ecosystem, possibly creating an environment that’s more favorable to it.

The body responds to all this destruction by raining inflammation upon the affected tissues — a normal part of the immune response that causes pus, pain, and irritation, but which also brings immune cells to the scene. Using our bodies as battlefields, trichomonads go mano a mano with immune cells called neutrophils. These immune cells are dwarfed by the larger trichomonads, but can slay their parasitic foes in just 10 minutes, taking down their Goliaths through simple teamwork. Multiple neutrophils surround a trichomonad and attack, taking bites out of the organism until it dies of its wounds. Last year, a group of researchers caught a neutrophil attack on camera for the first time — a battle in which immune cells descended upon a single trichomonad (dyed green) and ate it alive. It never stood a chance!

But trichomonads aren’t completely defenseless against our immune systems. They’re friends with bacteria called mycoplasmas — cousins of the sexually transmitted organism Mycoplasma genitalium — that are quite possibly nestled inside their bodies. It’s something of a symbiotic relationship, where mycoplasmas are sheltered from drugs and immune attack, and return the favor by helping to scavenge arginine from the urogenital environment. The immune system needs this chemical to kill microbes, so by hoarding the local supply, the dynamic trichomonad-mycoplasma duo can weaken our bodies’ defenses against it.

Treating Trich: Changes on the Horizon

Sexually active people can avoid trich by using condoms consistently and correctly on penises and shared penetrative sex toys. Transmission is also possible through direct vulva-to-vulva contact, or touching one’s genitals after fingering or fisting a partner’s vagina. In these cases, risk can be decreased by changing latex gloves between acts.

Luckily, trichomonads can be killed with drugs called metronidazole and tinidazole — although drug resistance is a possibility. At Planned Parenthood Arizona, trich is currently treated with 2 grams of metronidazole — a one-and-done single dose that can be administered in the health center. The single-dose strategy is easier for patients to follow, since they won’t have to worry about missing doses, and spend less time abstaining from sexual intercourse and alcohol, both of which reduce the effectiveness of the medication. If the infection doesn’t clear up, metronidazole is offered as a seven-day regimen. A recent clinical trial, however, showed that the seven-day regimen of metronidazole may be more effective than a single dose, and treatment guidelines might be changing in the near future to reflect these results.

If you have symptoms or think you’ve been exposed, or if you just want to make sure your STD testing is as thorough as it can be, you can request screening for both yourself and your partner at any Planned Parenthood health center. You can be tested by giving a urine sample, which can be checked by a lab, or by undergoing a physical exam in which a clinician takes a sample and examines it under a microscope right there in the center. And, if you’re being treated for trich, make sure to take the full course of drugs you were prescribed, which is necessary to guard against drug resistance and to make sure your infection is truly gone.


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