For many women, an unusual vaginal discharge or a persistent fishy smell is often mistaken for a yeast infection or bacterial vaginosis. Others choose to self-medicate, hoping the symptoms will disappear on their own. Yet behind these common complaints could be one of the world's most widespread — and least talked about — sexually transmitted infections (STIs).
Trichomoniasis, commonly known as "trich", is a curable STI caused not by bacteria or a virus but by a microscopic parasite known as Trichomonas vaginalis. Despite infecting millions of people worldwide each year, the infection often goes undetected because most people develop no symptoms, allowing it to spread silently between sexual partners.
According to the World Health Organisation (WHO), trichomoniasis is the most common non-viral sexually transmitted infection globally. In the United States alone, an estimated 3.7 million people are living with the infection, yet only about 30 per cent develop noticeable symptoms.
Dr Dennis Miskellah, a consultant gynaecologist, says the infection is far more common than many people realise.
"Trichomoniasis is caused by a parasite, not a bacterium or a virus," he explains. "After unprotected sexual intercourse with an infected partner, symptoms can appear anywhere between one week and one month, although most infected people never develop symptoms."
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Women are more likely than men to experience symptoms because the parasite thrives in the vaginal environment. When symptoms do occur, they can include vaginal itching, redness, discomfort during urination and a characteristic yellowish-green discharge that may be thin or frothy.
"The discharge often has a strong fishy smell," says Dr Miskellah. "When a woman presents with a yellow, frothy, foul-smelling discharge, trichomoniasis becomes one of the conditions we strongly suspect."
Men, on the other hand, rarely develop symptoms. Some may experience mild discomfort while urinating, but many remain completely unaware that they are infected.
"Because men frequently have no symptoms, they can unknowingly continue transmitting the infection to their sexual partners," he says.
The parasite is transmitted primarily through vaginal sexual contact. It spreads through infected vaginal fluids and semen during unprotected intercourse. It can also be transmitted through the sharing of contaminated sex toys if they are not properly cleaned or protected between users.
Diagnosis begins with a clinical examination. During a pelvic examination, doctors may notice inflammation of the cervix, sometimes described as a "strawberry cervix" because of its reddish appearance.
A vaginal swab is then collected and examined under a microscope to identify the parasite. Where microscopy fails to detect it, more sensitive laboratory tests, including culture or molecular testing, may be recommended.
Treatment is straightforward and highly effective. "The infection is curable," says Dr Miskellah. "The standard treatment is metronidazole."
He notes that women are usually prescribed a week-long course of medication, while many men can be treated with a single high-dose regimen, depending on clinical guidelines and the doctor's assessment.
However, treatment should never involve only one partner.
"Both partners must be treated at the same time," he emphasises. "If one partner remains untreated, reinfection can occur almost immediately."
Couples are also advised to avoid sexual intercourse until they have completed treatment and waited at least one additional week to ensure the infection has cleared completely.
Dr Miskellah cautions that many women assume every episode of fishy-smelling discharge is bacterial vaginosis (BV), leading some to delay proper testing.
"BV can also cause a fishy smell, but trichomoniasis is more likely to produce the characteristic yellow-green frothy discharge," he explains. "Sometimes the two infections can even occur together, which is why laboratory testing is important."
Left untreated, trichomoniasis can have serious health consequences, particularly for women.
The infection can ascend through the reproductive tract, causing pelvic inflammatory disease (PID), a condition that can damage the uterus and fallopian tubes.
"PID can result in chronic pelvic pain, scarring of the fallopian tubes and secondary infertility," says Dr Miskellah. "If the tubes become blocked, it may become difficult for a woman to conceive naturally."
Pregnant women are also at increased risk of complications.
"The infection has been associated with premature delivery, meaning the baby may be born before full term," he explains.
Beyond reproductive health, trichomoniasis also increases a person's vulnerability to acquiring other sexually transmitted infections, including HIV.
Dr Miskellah explains that the same behaviours that increase the risk of trichomoniasis — particularly unprotected sex with multiple partners — also increase the likelihood of HIV exposure. In addition, inflammation caused by the infection may make it easier for HIV to enter the body if exposure occurs.
One challenge in controlling trichomoniasis is that people who have been successfully treated can become infected again if they have sex with an untreated partner.
"You can definitely get it again," says Dr Miskellah. "Successful treatment does not provide immunity."
He urges people not to ignore persistent genital symptoms or rely solely on self-diagnosis.
"Not everyone with trichomoniasis will have discharge or itching. Sometimes there are no visible symptoms at all. The safest thing is to seek medical evaluation rather than guessing what the infection might be."
Although many people engage in oral sex, Dr Miskellah notes that the parasite responsible for trichomoniasis does not survive in the mouth or rectum, making transmission through oral sex extremely unlikely.
He also advises against practices that disrupt the vagina's natural environment.
"The vagina has its own healthy balance of bacteria," he explains. "Introducing substances such as douching products, saliva, or other fluids can alter its natural pH, reducing protective bacteria and allowing harmful organisms to thrive."
Ultimately, prevention remains the most effective defence.
Dr Miskellah recommends consistent condom use, mutually monogamous relationships where both partners know their STI status, prompt medical evaluation for unusual symptoms and ensuring that all sexual partners receive treatment whenever trichomoniasis is diagnosed.
"The important thing to remember is that someone can look completely healthy and still carry the infection," he says. "You cannot diagnose trichomoniasis by appearance alone. If you are sexually active and have concerns, get tested and seek treatment early."
Health experts say breaking the silence around trichomoniasis is just as important as treating it. Because the infection is both common and curable, early diagnosis and partner treatment remain the best tools for stopping its silent spread.