Trichomoniasis is an infection caused by the presence of a parasite, called trichomonas vaginalis.

The parasite is sexually transmitted, and upsets the balance of bacteria in the urethral or genital tract of the host. This then results in an infection.

On this page, you can read about:

What does trichomonas vaginalis look like?

The parasite has a rounded, pear-shaped body. At one end, it carries five flagella, or legs. It also has an undulating membrane on its flank. The parasite as a whole is between 7 and 9 micrometres long (a micrometre is a millionth of a metre), which makes it only just larger than a white blood cell. When the parasite finds a host, it replicates itself several times.

How is trichomonas vaginalis spread?

TV can be passed from one host to another through unprotected vaginal sexual intercourse, or through the shared use of sex toys. Oral and anal sex are not considered to be viable transmission routes.

A theory has been put forward by Indian doctors that postmenopausal women are more likely to be susceptible to TV, as lower levels of oestrogen provide favourable conditions (namely higher alkaline levels) for the parasite to spread.

What does the parasite do in the body?

When in the body, it latches to the urethral wall using its flagella, and secretes proteins which alter the bacterial balance of the infection site. The parasite also reproduces itself, and its replicants do the same. When the bacterial balance of the body becomes upset, this can lead to an infection and subsequently (but not always) symptoms.

The parasite sustains itself by synthesising proteins. TV can last for up to a whole day in semen or urine.

How does treatment kill the parasite?

Metronidazole is an antibiotic used in anaerobic and protozoal infections (such as TV). It works by inhibiting the parasite’s ability to replicate its own DNA. Once it cannot reproduce itself, the parasite then becomes weakened, and susceptible to the body’s immune system. When the parasite is killed off, the resulting infection then clears up.

If you are concerned that you may have an infection, or are experiencing symptoms of trichomoniasis, you should get tested for TV, or visit your nearest GUM clinic for further advice as soon as possible.

Page last reviewed:  07/10/2020 | Next review due:  10/10/2022