Trichomonas vaginalis (trichomoniasis)

Trichomonas vaginalis is a sexually transmitted disease (STD), although transmission by other routes (such as soiled towels) has been documented. There is no cyst in the life cycle, so transmission is via the trophozoite stage only. Most people infected with trichomoniasis are asymptomatic. It is one of the most frequent sexually transmitted diseases in man. 30 to 50 % of all women in western countries may be infected. In males the infection normally does not lead to any symptoms, while in females this may lead to an increased secretion, characterized by a white discharge from the genital tract and itching. Diagnosis depends on finding trophozoites in secretions of the genital tract from men or women. In cases where the numbers of organisms are very low, the trophozoites can be cultured to increase their numbers.

Light microscopic picture of Trichomonas vaginalis in culture

Trichomonas vaginalis is a facultative anaerobic protozoan parasite that has no mitochondria or peroxisomes. Trichomoniasis is treated with metronidazole (Flagyl). The drug is reduced inside the parasite by the enzyme hydrogenase located in typical organelles called hydrogenosomes. When the drug reacts with traces of oxygen present in the organism it forms oxygen radicals that rapidly kill the parasite. Metronidazole is also used for the treatment of Giardia and Entamoeba infections and for infections by some anaerobic bacteria.

A trophozite of Trichomonas vaginalis from culture. The four flagella and single nucleus are visible. The dark median rod is the axostyle which is characteristic of the trichomonads; approximate size = 26 µm.