What Causes Trichomonas Infection?
Trichomoniasis is caused by the protozoan parasite Trichomonas vaginalis (T. vaginalis), which is transmitted through sexual contact. 1, 2
Causative Organism
Trichomonas vaginalis is a flagellated protozoan parasite that infects the urogenital tract 1, 3, 2. This is the sole causative agent of trichomoniasis, distinguishing it from other causes of vaginitis like bacterial vaginosis (caused by overgrowth of anaerobic bacteria) or candidiasis (caused by yeast).
Mode of Transmission
The infection is sexually transmitted 1, 2. Key transmission characteristics include:
- Sexual contact is the primary route of transmission - the parasite is passed between sexual partners during intercourse
- Most infected men are asymptomatic, serving as reservoirs for transmission 1, 3, 2
- Treatment of sex partners is essential to prevent reinfection and achieve cure 1, 2
The CDC guidelines consistently emphasize that patients must avoid sexual contact until both they and their partners complete treatment and become asymptomatic 1, 2.
Pathogenesis
The parasite causes infection through:
- Cytoadherence to urogenital epithelial cells for colonization 4, 5
- Direct damage to host tissue through parasite-mediated killing of host cells 4
- Activation of inflammatory responses including the NLRP3 inflammasome and TLR3-mediated pathways 6
- Secretion of extracellular vesicles that modulate host immune responses 6, 5
Risk Factors
While the direct cause is the parasite itself, certain factors increase acquisition risk:
- Multiple sexual partners - strongly associated with infection 1, 7
- Having a new sexual partner 1
- Lack of barrier contraception (implied by sexual transmission route)
Clinical Context
In women, T. vaginalis typically causes a diffuse, malodorous, yellow-green vaginal discharge with vulvar irritation 1, 3, 2, though some women have minimal or no symptoms 2. The infection has been associated with adverse pregnancy outcomes including premature rupture of membranes, preterm delivery, and low birth weight 1, 2.
The key clinical pitfall: Do not confuse trichomoniasis with bacterial vaginosis or candidiasis - while all three cause vaginal discharge, only trichomoniasis is caused by a protozoan parasite and requires specific antiprotozoal treatment with metronidazole 1, 2.