What is trichomoniasis?
Trichomoniasis is an extremely common, sexually transmitted infection (STI) caused by the protozoan parasite, Trichomonas vaginalis. Around 3.1% of women of reproductive age in the United States are infected with T. vaginalis; with an estimated 180 million new infections acquired worldwide per year. Females can acquire the disease from infected males or females; but males usually acquire it only from infected females.
The incubation period is generally between 4 and 28 days. Trichomoniasis is a marker of high-risk sexual behaviour. Co-infection with other STIs is common, especially Chlamydia trachomatis and Neisseria gonorrhoeae (gonorrhoea).
What are the clinical features of trichomoniasis?
Trichomoniasis in females
Around half of infected females will have no symptoms from trichomoniasis. Females can be asymptomatic carriers for months or years.
- Most symptomatic females have a purulent (yellow), thin, vaginal discharge with an offensive odour
- The classic symptom is a yellow-green, frothy, foul-smelling discharge, but this is present in less than 10% of symptomatic females
- Other symptoms include pruritus vulvae (itchy vulva), and vaginal burning or itch
- Pain and/or bleeding with sexual intercourse can occur
- The urethra is often involved producing urethral discharge, and painful and frequent urination
- Lower abdominal pain can occur rarely
Physical signs of trichomoniasis include:
- Erythema (redness) of the vulva and vagina with discharge and offensive odour
- Elevated vaginal pH (above 4.5) in most females, unlike in vulvovaginal candidiasis when it is reduced (below 4.5)
- Colpitis macularis (strawberry cervix) may be present. This refers to punctate haemorrhages (small red dots) that are occasionally visible on the cervix (or vaginal walls). This is the most specific sign of trichomoniasis, but is rarely detected without the aid of colposcopy.
Trichomoniasis in males
T. vaginalis is present in 30-70% of the male partners of infected females. Most infected males (>90%) will have no symptoms. When symptoms are present they are usually a result of urethritis (inflammation of the urethra) and include irritation inside the penis, scant, thin discharge, or slight burning after urination or ejaculation. These symptoms usually disappear within a few weeks without treatment. However, an infected male (even those who have never had symptoms) can continue to infect or re-infect a female sexual partner until he has been treated.
Up to 11% of cases of non-gonococcal urethritis in males are caused by T. vaginalis.
What complications can trichomoniasis cause?
- Trichomoniasis increases the likelihood of HIV acquisition and transmission, so that an individual with trichomoniasis has increased susceptibility to HIV infection; and an HIV-positive individual co-infected with T. vaginalis is more likely to transmit HIV to sexual partners.
- Potential complications in females include increased risk of post-hysterectomy infections, tubal infertility, and cervical cancer.
- In pregnancy, T. vaginalis infection has been associated with low birth weight, premature rupture of membranes, and preterm delivery. However treatment of asymptomatic infection in pregnancy has not been shown to reduce these complications.
- T. vaginalis can be transmitted from mother to baby during delivery and cause fever, breathing problems, urinary tract infection, and in girls, vaginal discharge. Infection usually resolves spontaneously during the neonatal period.
- Potential complications in men include infection of the prostate, foreskin, and epididymis, as well as decreased sperm motility.
How is trichomoniasis diagnosed?
The following methods can be used to detect T. vaginalis:
- In men a urethral swab and in women a high vaginal swab (can be self-collected) can be sent to the laboratory for culture of the organism. It is harder to detect T. vaginalis in men and false negatives are common. Reliability may be improved by combining a urethral swab with a urine sample for culture. It is often recommended that male sexual partners of infected females receive empiric treatment (without relying on culture results); however a full STI screen is still recommended due to the increased likelihood of co-infection with other STIs.
- Wet mount microscopy – a small amount of vaginal discharge is placed on a slide with a few drops of saline and immediately examined under a microscope. The organism may be visible, but only for 10 to 20 minutes after collection of the sample. Excess white blood cells may also been seen in this fluid and indicates accompanying inflammation.
- Cervical smear tests sometimes note the presence of trichomonads, however false positives can occur (less likely with liquid based cytology) so this should be confirmed with culture. A cervical smear test cannot be used as a screening test for trichomoniasis, due to the high number of false negatives.
What is the treatment of trichomoniasis?
- The oral antibiotic, metronidazole, is prescribed and is safe for use in pregnancy and lactation. Tinidazole or ornidazole are alternatives for males and non-pregnant, non-lactating females.
- Sexual partners also require treatment to prevent re-infection. A male sexual partner should be treated even if he has no symptoms.
- Patients should avoid sex until they and their sexual partners complete treatment and have no symptoms (usually about one week).
How is trichomoniasis prevented?
There is little immunity gained as a result of T. vaginalis infection, i.e. having had trichomoniasis once does not protect a person from getting it again. Safe sex practices, including limiting the number of sexual partners and using condoms, can reduce the transmission of T. vaginalis.