Classification and types
The genus Trichomonas includes several species inhabiting the human body. They differ in localization site and pathogenicity:
- Trichomonas vaginalis (vaginal/urogenital). The main human pathogen causing urogenital trichomoniasis (strict anthroponosis).
- Pentatrichomonas (Trichomonas) hominis (intestinal). Affects the gastrointestinal tract, provoking colitis and enteritis, but only in immunocompromised individuals.
- Trichomonas tenax (oral). A harmless commensal of the oral cavity that does not cause disease.
Structure and life cycle
The life cycle of trichomonads is extremely simple: they exist only in the vegetative stage (trophozoite) and reproduce by longitudinal fission. Due to the lack of a cyst stage, they quickly die in the external environment.
Morphologically, they are pear-shaped cells measuring 8–40 by 3–14 µm. For movement, the parasite uses:
- Flagella. Five at the anterior end of the cell.
- Undulating membrane. A special wave-like fold on the side, connected to one of the flagella and reaching approximately the middle of the body.
Inside the cell, acting as support, runs the axostyle — a dense hyaline filament that protrudes at the posterior end as a spine. Trichomonads feed through the cell mouth (cytostome), which has the appearance of a small slit.
Pathogenesis of urogenital trichomoniasis
The causative agent (T. vaginalis) is transmitted mainly sexually, less often vertically (during childbirth) or via contact-domestic routes (through damp hygiene items). The incubation period ranges from 7 to 10 days, sometimes extending up to a month.
Upon entering the urogenital tract, the trichomonad secretes invasion factors — hyaluronidase and cell-detaching factor, which help it penetrate under the epithelium. Inflammation develops: urethritis, vaginitis, or prostatitis. Patients complain of itching, pain, and purulent-serous discharge, though the infection is often asymptomatic.
An important feature of T. vaginalis is its ability to undergo incomplete phagocytosis. The parasite engulfs other bacteria (e.g., gonococci or chlamydia) but does not digest them. Inside the trichomonad, the bacteria are protected from antibiotics and immune cells, which greatly complicates the treatment of coinfections.
Laboratory diagnostics
The main method for detecting trichomonads is microscopy. Urine sediment, prostate secretion, or urethral discharge is used for analysis.
Two types of preparations are used:
- Native (live) smears. Prepared by the "hanging drop" method with warm saline. Using a phase-contrast microscope (×40 objective), cells the size of a leukocyte are sought, making characteristic movements with their flagella and membrane.
- Stained smears. Stains are used (methylene blue or Romanowsky-Giemsa).
In chronic cases, culture on SCD medium is used, along with serology (ELISA, IFA) and PCR diagnostics.
Treatment and Prevention
Antimicrobial drugs from the nitroimidazole group are used for therapy, such as metronidazole, ornidazole, tinidazole, or nimorazole.
General prevention is standard for all sexually transmitted infections. A specific vaccine, Solcotrichovac, based on lactic acid bacteria (Lactobacillus acidophilus), has been developed for women.
Briefly: answers to topical questions
What morphological differences (size, number of flagella, membrane length) exist between vaginal, intestinal, and oral trichomonads?
Morphological differences are described only for vaginal and intestinal trichomonads; characteristics of the oral trichomonad (Trichomonas tenax) are absent in the sources.
| Sign | Trichomonas vaginalis | Trichomonas hominis |
|---|---|---|
| Size | 8–40 × 3–14 µm; another source specifies a length of 7–23 µm for the urogenital trichomonad | 8–20 × 3–14 µm |
| Flagella | 5 at the anterior end | 4 free, 5th runs along the body margin |
| Undulating membrane | Reaches the middle of the body | Extends far beyond the end of the body and ends in a free flagellum |
On which elective nutrient media is Trichomonas vaginalis cultivated?
For the cultivation of Trichomonas vaginalis in laboratory diagnostics, a specialized nutrient medium (SCD medium) is used.
- SCD medium — consists of a salt solution, casein hydrolysate, yeast, and maltose.
This culture method (inoculation) is used primarily for detecting chronic forms of urogenital trichomoniasis.
What is the mechanism of the antiprotozoal action of metronidazole on trichomonad cells?
Metronidazole is activated: the enzyme systems of trichomonads reduce its nitro group.
Pathways of cell damage:
- Respiratory disruption — the reduced drug incorporates into the respiratory chain and blocks flavoproteins, disrupting respiratory processes.
- DNA damage — during the reduction of the nitro group, free radicals are formed, exerting a direct toxic effect on DNA and suppressing its replication.
Class and exam questions
Why is it impossible to contract trichomoniasis in a dry sauna or through dry towels?
Trichomonads do not form cysts and exist exclusively in the vegetative form; therefore, they are extremely fragile in the external environment and rapidly die upon drying.
How does a trichomonad complicate the course of other sexually transmitted diseases?
It is capable of phagocytosing (engulfing) other pathogens, such as gonococci and chlamydia. Inside the trichomonad, these bacteria remain alive and protected from antibiotics and the immune system.
Why are the "hanging drop" method and warm saline needed in diagnostics?
This method allows for the observation of live parasites. Warm solution supports their viability, allowing one to see the characteristic motility of the flagella and undulating membrane.
What else to study on this topic
- Mechanism of action of nitroimidazoles on parasite cells
- Features of phase-contrast microscopy in parasitology
- Composition and principle of action of the Solcotrichovac vaccine
- Differential diagnostics of trichomonads and leukocytes in a smear
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