STD Awareness: Drug-Resistant Trichomoniasis

Two trophozoites of Trichomonas vaginalis, the causative agent of trichomoniasis. Image from the CDC’s Parasite Image Library.

Trichomonas vaginalis organisms, which cause trichomoniasis. Image: Parasite Image Library, CDC

You’ve probably heard of MRSA, which is a strain of Staphylococcus aureus that evolved resistance to all kinds of antibiotics. You also might have heard of other “superbugs,” like Clostridium difficile, aka “C. diff,” or the emerging strains of bacteria that cause antibiotic-resistant gonorrhea. However, other infectious diseases are slowly evolving drug resistance too, but they’re not grabbing headlines. One such disease is trichomoniasis.


We are only starting to learn about drug-resistant trich — and what it means for those who have it.


Trichomonas vaginalis is the single-celled parasite that causes trichomoniasis, or trich (pronounced “trick”). Symptoms can include vaginal discharge (which might have a bad odor), penile burning or discharge, spotting, and itching or swelling in the genital area — but around 70 percent of trich infections are asymptomatic.

Despite its appearance on our list of 10 STDs you’ve probably never heard of, trich is actually the most common curable sexually transmitted disease out there — around 3.7 million Americans are currently infected with trich. When you consider that trich rarely has symptoms, its ubiquity might not even seem all that surprising — there are millions of infections, right under our noses, but mostly unknown and not being aggressively screened for. STD testing doesn’t always include screening for trich, especially in males, who usually don’t have symptoms and can transmit it to others unknowingly. This might not be so bad if trich didn’t cause complications with pregnancy or make it easier to be infected with HIV.

Luckily, the parasite that causes trich can be killed with certain drugs, namely metronidazole and tinidazole. Metronidazole has been the go-to treatment since the early 1960s, but a relatively new drug called tinidazole is also in use. All drugs used to treat trich are in the 5-nitroimidazole “family,” which the parasite absorbs and converts into chemicals that are toxic to their cells. The exact mechanism of action is unknown, but it’s thought that these drugs disrupt T. vaginalis’ DNA or its ability to use proteins.

So, is T. vaginalis evolving resistance to these drugs? Yes, but no one’s sounding alarm bells just yet. Usually, trich is cured with one dose of metronidazole. A case of trich that is thought to be drug-resistant is usually cured with a higher dose of metronidazole. The catch is that metronidazole has side effects, such as nausea, that can be amplified at higher doses. And, if that higher dose doesn’t even work, a different drug might be used. However, the fact that all trich drugs are chemically similar makes some researchers wary, because if T. vaginalis keeps honing its resistance to them, we might not have viable alternatives if it turns out we need them.

Currently, drug-resistant trich is rare, and recurrent infections are usually due to reinfection from an untreated (and usually asymptomatic) partner. But, if evolution is our guide, the problem could grow over time. If you are treated for trich, the best thing you can do is take the full course of drugs that you are prescribed — don’t stop early, even if your symptoms have gone away. Otherwise, a few especially tough organisms might be hanging in there, giving rise to descendants who are just as tough as they are — it’s called survival of the fittest. Responsible antibiotic use is one weapon we have against drug resistance.

Luckily, completely drug-resistant trichomoniasis is — so far — not a major problem. For example, one study, conducted in six U.S. cities and published in 2012, found low levels of metronidazole resistance in 4.3 percent of cases studied, but parasites were susceptible to higher doses, as well as to tinidazole. Another study only found two cases of “low-level” metronidazole resistance out of 82 samples, and a British study found that metronidazole resistance had grown from 0.38 percent in 1999 to 3.5 percent in 2002. One study in Alabama recorded a metronidazole resistance rate that approached 10 percent. It’s hard to know what these numbers mean without more context, though.

Drug-resistant strains of a disease aren’t necessarily incurable — it might just take longer for the drugs to do their job. While some trich infections are stubborn, they may be treated with longer courses of medications or different combinations and dosages of drugs. Right now, researchers aren’t quite sure what drug-resistant trich means for the people who have it, but some are looking into other methods of treatment, involving creams or suppositories that are inserted directly into the vagina. Unfortunately, these therapies have not been extensively studied (most cases are anecdotal), either for efficacy or side effects.

Drug-resistant cases of trich aren’t being monitored like antibiotic-resistant gonorrhea is. Researchers are rather haphazardly studying populations around the world, from a public health clinic in Birmingham, Alabama to a GUM clinic in Birmingham, England. (“GUM” is Britspeak for genito-urinary medicine.) Making broad generalizations about the evolution of drug-resistant trich is difficult when only random pockets of the world’s population are being studied — not just in cities named Birmingham, but others, too, such as New York, Philadelphia, and Seattle.

Sexually active people can avoid trich by using condoms consistently and correctly — on penises and shared penetrative sex toys. Transmission is also possible via direct vulva-to-vulva contact, or touching one’s genitals after fingering or fisting a partner’s vagina; in such cases risk can be decreased by changing latex gloves between acts. Furthermore, since trich is so often asymptomatic, you can request screening for both yourself and your partner. And, if you’re being treated for trich, make sure to take the full course of drugs that you were prescribed. You might consider retesting to make sure the treatment took. A health care provider, such as those at Planned Parenthood, can give you further advice and answer any questions you might have.

More information about trichomoniasis is at the CDC’s website. You can seek diagnosis and treatment at any Planned Parenthood health center.


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3 thoughts on “STD Awareness: Drug-Resistant Trichomoniasis

  1. Options for drug treatment for a patient who
    Has a proven allergy to metronidazole?
    Patient has trichomonas vaginitis.
    Clines de? Oral cleocin? Sulfa bag cream for symptom removal? Thank you

    • Hi Jon. We can’t give medical advice on this blog, but you can check out the CDC’s treatment guidelines, which recommends “metronidazole desensitization according to a published regimen and in consultation with a specialist.” The page includes a link to further information.

  2. Hi I took Metronidazole 4 pills at once like planned parenthood said on Monday the 13 and had sex with a condom when I research more into this I realize you’re not supposed to have sex for seven days so when I went back but this time to my regular doctor and got more pills and restarted the treatment on wed the 15 but it’s been more than enough days and the itchiness doesn’t go away at times I can’t handle the itch is that normal I would think I would feel better by now

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