Trichomonas vaginalis is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countries. Infection rates in men and women are similar but women are usually symptomatic, while infections in men are usually asymptomatic. Transmission usually occurs via direct, skin-to-skin contact with an infected individual, most often through vaginal intercourse. It is estimated that 160 million cases of infection are acquired annually worldwide. The estimates for North America alone are between 5 and 8 million new infections each year, with an estimated rate of asymptomatic cases as high as 50%. Usually treatment consists of either metronidazole or tinidazole. More recent studies on Trichomonas vaginalis have shed light on the parasite's evolution, genomic complexity, and pathogenesis processes. New population studies and genomic sequences illustrate the genetic variability of the parasite and the parasite's possible resistance to treatment. Understanding of host-pathogen interaction and prevention strategies remains a driving force behind public health.
Clinical
History
Alfred Francois Donné (1801–1878) was the first to describe a procedure to diagnose trichomoniasis through "the microscopic observation of motile protozoa in vaginal or cervical secretions" in 1836. He published this in the article entitled, "Animalcules observés dans les matières purulentes et le produit des sécrétions des organes génitaux de l'homme et de la femme" in the journal, Comptes rendus de l'Académie des sciences. With it, he created the binomial name of the parasite as Trichomonas vaginalis. 80 years after the initial discovery of the parasitic protozoan, Hohne declared Trichomoniasis as a clinical entity in 1916.
Signs and symptoms Most women (85%) and men (77%) infected with T. vaginalis do not have symptoms. Half of these women can develop symptoms within 6 months and can have vaginal erythema, dyspareunia, dysuria, and vaginal discharge, which is often diffuse, malodorous, and yellow-green, along with itching in the genital region. Strawberry cervix occurs in about 5% of women. In men, it can cause urethritis, epididymitis and prostatitis.
Complications Some of the complications of T. vaginalis in women include preterm delivery, low birth weight, and increased mortality as well as predisposing to human immunodeficiency virus infection (AIDS), and cervical cancer. T. vaginalis can be seen in diverse locations within the body, such as in the urinary tract, fallopian tubes, and pelvis and can cause pneumonia, bronchitis, and oral lesions.
Diagnosis
Classically, with a cervical smear, infected women may have a transparent "halo" around their superficial cell nucleus but more typically the organism itself is seen with a, "slight cyanophilic tinge, faint eccentric nuclei, and fine acidophilic granules." It is unreliably detected by studying a genital discharge or with a cervical smear because of their low sensitivity. T. vaginalis is also routinely diagnosed via a wet mount, in which motility is observed. Currently, the most common method of diagnosis is via overnight culture, with a sensitivity range of 75–95%. Newer methods, such as rapid antigen testing and transcription-mediated amplification, have even greater sensitivity, but are not in widespread use.
Prevention and Treatment Infection is treated and cured with metronidazole or tinidazole. The CDC recommends a one time dose of 2 grams of either metronidazole or tinidazole as the first-line treatment; the alternative treatment recommended is 500 milligrams of metronidazole, twice daily, for seven days if there is failure of the single-dose regimen. Medication should be prescribed to any sexual partner(s) as well because they may be asymptomatic carriers. Trichomoniasis ranks as the most prevalent non-viral sexually transmitted disease, and there were about 156 million new cases in 2020 reported worldwide. It is a curable infection that occurs through unprotected intercourse. Measures for prevention include the use of a condom consistently and screening in sexually active participants. Symptoms include urethral or vaginal irritation, unusual discharge, itching in the genitals, frequent urination, and dysuria. Antigen detection and the use of nucleic acid amplification tests are able to be used in diagnosis. A single dose of oral metronidazole or tinidazole and other regimens for resistant strains are the recommended treatments. Despite the relatively low rate of resistance, it remains a rising public concern. There is no vaccine for trichomoniasis and the prevention and early treatment of the disease are hence vital.
Pathogenesis T. vaginalis causes a very common sexually transmitted disease by adhering to vaginal epithelial cells and breaking them down. It secretes extracellular vesicles that disrupt immune function and increase adhesion. Some strains have intracellular viruses or bacteria within them that worsen infections. The parasite is associated with disruptions to vaginal microflora. Neutrophils are the primary immune cell associated with infection, which can kill the parasite through trogocytosis.
Morphology
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