Infection of the parasite Trichomonas vaginalis

Illustration of the parasite Trichomonas vaginalis trophozoite representing the STI Trichomoniasis

It’s one of the most common STIs in the world but more often than not, people don’t even know they have it

What is trichomoniasis? 

Trichomoniasis, also known as trich, is a sexually transmitted infection (STI) caused by an infection of the parasite Trichomonas vaginalis [1]. 

How common is it?

Trich is one of the most common STIs in the world affecting approximately 3.7 million people in the U.S. alone [3]. It’s good at going incognito, with 70% of those infected not showing any symptoms at all. In addition, men are more likely to fall into the asymptomatic category than women [3]. 

Given the high likelihood that an infected person won’t show any symptoms or might only have very mild ones, it’s no surprise that trich often goes untreated. 

What causes trich and what are the risk factors?

Trich is caused by Trichomonas, a single-cell parasite that can be passed between people during sexual intercourse. This parasite isn’t a worm, and the infection isn’t bacterial or viral like most other common diseases [2,4]. 

Even if the infected person shows no symptoms, they can still pass along the infection. As a result, sex with new or multiple partners as well as unprotected sex puts both men and women at a higher risk for all STIs including trich [3]. Also, and as a general rule, anything that disrupts the natural balance of your vaginal microbiome can put you in a state of dysbiosis leaving you susceptible to multiple types of infections including STIs.

What are the symptoms?

For those individuals that do show symptoms, they tend to show up anywhere for 5 to 28 days after being infected [3]. Symptoms for both men and women include discomfort during sex, pain during urination and itching. Along with vaginal itching, women might also experience other signs of inflammation such as burning and general soreness or redness of the genital area. There is often also a change in vaginal discharge. It could be clear, white, yellow or green, and might also have the same fishy smell associated with bacterial vaginosis.

How is trich diagnosed?

The Trichomonas vaginalis parasite can be easily spotted under a microscope if you know what to look for [2]. The sample would be taken from a vaginal swab. 

What are the treatment options?

Antibiotics like Metronidazole (Flagyl) or Tinidazole are often prescribed and tend to work well. However, about 20% of people end up getting re-infected within three months of treatment. 

Can trich lead to other complications?

Trich is stubborn and without treatment it can hang around for months or even years. Untreated, it can cause vaginal inflammation which makes you more vulnerable to other STIs including HIV [4].

In pregnant women, trich can cause preterm birth [6]. The baby of an infected mother is also more likely to weigh less than is considered healthy. 

What can be done to prevent trich?

To reduce your chances of getting an STI like trich, practice safe sex by always discussing sexual health with your partner, using barrier protection correctly (such as a condom or dental dam), and getting tested regularly. To protect yourself against infections, avoid disrupting the balance of protective bacteria in the vaginal microbiome by limiting the use of douches as well as the use of scented soaps, tampons or pads.

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1. Trichomoniasis [Internet]. [cited 17 September 2020]. Available from:

2. Trichomoniasis - Symptoms and causes[Internet]. Mayo Clinic. 2020 [cited 17 September 2020]. Available from:

3. Trichomoniasis - STD informationfrom CDC [Internet]. 2020 [cited 17 September 2020]. Available from:

4. Boris S, Barbés C. Role played bylactobacilli in controlling the population of vaginal pathogens. Microbes andInfection. 2000;2(5):543-546.

5. Phukan N, Parsamand T, Brooks A,Nguyen T, Simoes-Barbosa A. The adherence ofTrichomonas vaginalisto hostectocervical cells is influenced by lactobacilli. Sexually TransmittedInfections. 2013;89(6):455-459.

6. KimT, Young M, Goggins E, Williams R, HogenEsch E, Workowski K et al. Trichomonasvaginalis in Pregnancy. Obstetrics & Gynecology. 2020;135(5):1136-1144.

Written by Aisha Ommaya, science comms officer with Juno Bio

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