Trichomonas vaginalis is a single-celled parasitic organism responsible for trichomoniasis, a common sexually transmitted infection (STI). This parasite infects the genitourinary tract in both men and women. As the most prevalent non-viral STI, an estimated 156 million new cases occurred worldwide in 2020. Understanding this widespread infection is important due to its implications for health.
Key Visual Features
Under a microscope, Trichomonas vaginalis exhibits distinct characteristics. The parasite is typically pear-shaped or oval, measuring approximately 10 to 20 micrometers in length and 2 to 14 micrometers in width. This size is slightly larger than a white blood cell, making it visible with standard light microscopy.
A defining feature is its five flagella, which are whip-like appendages used for movement. Four of these flagella protrude from the parasite’s anterior end, propelling it through fluid. The fifth flagellum extends backward along the organism’s body, forming part of the undulating membrane.
This fin-like extension contributes to the parasite’s characteristic motility. The combination of flagellar action and the undulating membrane gives Trichomonas vaginalis a distinctive jerky, tumbling, or quivering movement when observed in fluid samples. The axostyle, a rigid, rod-like support, protrudes from the posterior end and may aid in attachment to host tissues.
How They Are Detected
Medical professionals employ several methods to identify Trichomonas vaginalis. Wet mount microscopy is a commonly used technique. This involves examining a fresh sample of vaginal fluid or urethral discharge directly under a microscope for the presence of the parasite’s motile forms.
While quick and inexpensive, wet mount microscopy has limitations, particularly a lower sensitivity ranging from 44% to 68%, meaning it can miss infections, especially in cases with low parasite numbers or in men. Nucleic Acid Amplification Tests (NAATs) are more advanced diagnostic tools. These tests detect the parasite’s genetic material, such as DNA or RNA, and are considered the gold standard for diagnosis due to their high accuracy, with sensitivities often exceeding 95%.
Rapid antigen detection tests are also available, offering quick results within 10 to 15 minutes by identifying specific Trichomonas vaginalis antigens from vaginal swabs. Although less sensitive than NAATs, these rapid tests provide a faster alternative to traditional wet mounts.
Laboratory culture, where samples are grown in a special medium, offers higher sensitivity than wet mount but takes several days for results.
The Impact of Trichomonas Infection
Many individuals with trichomoniasis experience no symptoms, with estimates suggesting up to 70% of infected people remain asymptomatic. When symptoms do occur, they typically develop between 5 and 28 days after exposure, though onset can be delayed.
In women, symptoms commonly include a foul-smelling vaginal discharge, which can be thin, frothy, and vary in color. Other manifestations may involve genital itching, burning, soreness, redness, discomfort during urination, or pain during sexual intercourse. Men are frequently asymptomatic, but if symptoms arise, they can include itching or irritation inside the penis, burning during urination or after ejaculation, or a clear or pus-like discharge.
Untreated trichomoniasis can lead to several complications. It increases the risk of acquiring or transmitting other sexually transmitted infections, including HIV, partly by causing genital inflammation. In women, the infection is associated with an increased risk of pelvic inflammatory disease (PID), which can cause chronic pelvic pain and potentially affect fertility. For pregnant individuals, trichomoniasis can contribute to adverse outcomes such as preterm delivery and low birth weight in infants.