Trichomonas vaginalis is a type of parasite spread through sexual intercourse. Trichomonas is classed as a protozoan, and is a single-celled organism with flagella. Flagella are appendages stretching from the body, similar to limbs. Trichomonas has four flagella at the front and a single flagellum at the back, giving a characteristic appearance to the organism. The flagella are used for movement, attaching to tissues and causing damage.

Trichomonas is spread through sexual activity and lives in the urethra of men and women and the vagina of women.

Trichomonas can increase the risk of:

  • Contracting HIV by damaging the vaginal mucosa
  • Bacterial vaginosis
  • Cervical cancer
  • Pelvic inflammatory disease
  • Pregnancy-related complications such as preterm delivery.



Up to 50% of cases of trichomoniasis are asymptomatic. When symptoms occur, they are non-specific:

  • Vaginal discharge
  • Itching
  • Dysuria (painful urination)
  • Dyspareunia (painful sex)
  • Balanitis (inflammation to the glans penis)

The typical description of the vaginal discharge is frothy and yellow-green, although this can vary significantly. It may have a fishy smell.

Examination of the cervix can reveal a characteristic “strawberry cervix” (also called colpitis macularis). A strawberry cervix is caused by inflammation (cervicitis) relating to the trichomonas infection. There are tiny haemorrhages across the surface of the cervix, giving the appearance of a strawberry.

Testing the vaginal pH will reveal a raised ph (above 4.5), similar to bacterial vaginosis.



The diagnosis can be confirmed with a standard charcoal swab with microscopy (examination under a microscope).

Swabs should be taken from the posterior fornix of the vagina (behind the cervix) in women. A self-taken low vaginal swab may be used as an alternative.

A urethral swab or first-catch urine is used in men.



Patients should be referred to a genitourinary medicine (GUM) specialist service for diagnosis, treatment and contact tracing.

Treatment is with metronidazole.


Last updated July 2020