Trichomonas vaginalis

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Trichomonas vaginalis
Trichomonas vaginalis observed by scanning electron microscopy
Trichomonas vaginalis observed by scanning electron microscopy showing the axostyle (ax), the anterior flagella (af) and the undulating membrane (rf).[1]
Scientific classification Edit this classification
Domain: Eukaryota
Phylum: Metamonada
Order: Trichomonadida
Family: Trichomonadidae
Genus: Trichomonas
Species:
T. vaginalis
Binomial name
Trichomonas vaginalis
(Donné 1836)

Trichomonas vaginalis is an

WHO has estimated that 160 million cases of infection are acquired annually worldwide.[3] 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%.[4] Usually treatment consists of metronidazole and tinidazole.[5]

Clinical

T. vaginalis protozoa. Colorized SEM
T. vaginalis protozoa.SEM
The structure of T. vaginalis
Main article: Trichomoniasis

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.[6] With it, he created the binomial name of the parasite as Trichomonas vaginalis.[7]

Mechanism of infection

Trichomonas vaginalis from a vaginal swab. This is a heavy infection; there were probably thousands of trichomonads in the vagina.

Trichomonas vaginalis, a parasitic protozoan, is the etiologic agent of trichomoniasis, and is a sexually transmitted infection.[3][8] More than 160 million people worldwide are annually infected by this protozoan.[3]

Symptoms

Pap smear, showing infection by Trichomonas vaginalis. Papanicolaou stain, 400×

Trichomoniasis, a sexually transmitted infection of the urogenital tract, is a common cause of vaginitis in women, while men with this infection can display symptoms of urethritis as well as symptoms of prostate infection.[9] 'Frothy', greenish vaginal discharge with a 'musty' malodorous smell is characteristic.[10]

Signs

Only 2% of women with the infection will have a "strawberry" cervix (colpitis macularis, an erythematous cervix with pinpoint areas of exudation) or vagina on examination.[11][12][13] This is due to capillary hemorrhage.[14]

Complications

Some of the complications of T. vaginalis in women include:

AIDS, and cervical cancer.[15] T. vaginalis has also been reported in the urinary tract, fallopian tubes, and pelvis and can cause pneumonia, bronchitis, and oral lesions. Condoms are effective at reducing, but not wholly preventing, transmission.[16]

Trichomonas vaginalis infection in males has been found to cause asymptomatic urethritis and prostatitis.[17] It has been proposed that it may increase the risk of prostate cancer; however, evidence is insufficient to support this association as of 2014.[17]

Diagnosis

A single trichomonas by phase contrast microscopy
Trichomonas vaginalis Gram stain (arrows)

Classically, with a

sensitivity. T. vaginalis is also routinely diagnosed via a wet mount, in which "corkscrew" motility is observed. Currently, the most common method of diagnosis is via overnight culture,[19][20] with a sensitivity range of 75–95%.[21] Newer methods, such as rapid antigen testing and transcription-mediated amplification, have even greater sensitivity, but are not in widespread use.[21] The presence of T. vaginalis can also be diagnosed by PCR, using primers specific for GENBANK/L23861.[22]

Treatment

Infection is treated and cured with metronidazole[23] 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.[24] Medication should be prescribed to any sexual partner(s) as well because they may be asymptomatic carriers.[10][25]

Morphology

Trichomonas vaginalis May-Grünwald-Giemsa staining. The spike-like axostyle can be seen on the left.

Unlike other parasitic protozoa (

hydrogenosomes.[9]

While T. vaginalis does not have a cyst form, organisms can survive for up to 24 hours in urine, semen, or even water samples. A nonmotile, round, pseudocystic form with internalized flagella has been observed under unfavorable conditions.[12] This form is generally regarded as a degenerate stage as opposed to a resistant form,[12] although viability of pseudocystic cells has been occasionally reported.[27] The ability to revert to trophozoite form, to reproduce and sustain infection has been described,[28] along with a microscopic cell staining technique to visually discern this elusive form.[29]

Trichomonas vaginalis from a human vagina x 400

Protein function

T. vaginalis lacks

malate to hydrogen and acetate in an organelle called the hydrogenosome.[30]

Virulence factors

One of the hallmark features of T. vaginalis is the adherence factors that allow

collagen IV.[32]

Genome sequencing and statistics

The T. vaginalis genome is approximately 160

transposable elements, reflecting a massive, evolutionarily recent expansion of the genome. The total number of predicted protein-coding genes is ~98,000, which includes ~38,000 'repeat' genes (virus-like, transposon-like, retrotransposon-like, and unclassified repeats, all with high copy number and low polymorphism). Approximately 26,000 of the protein-coding genes have been classed as 'evidence-supported' (similar either to known proteins, or to ESTs), while the remainder have no known function. These extraordinary genome statistics are likely to change downward as the genome sequence, currently very fragmented due to the difficulty of ordering repetitive DNA, is assembled into chromosomes, and as more transcription data (ESTs, microarrays) accumulate. But it appears that the gene number of the single-celled parasite T. vaginalis is, at minimum, on par with that of its host H. sapiens.[citation needed
]

In late 2007 TrichDB.org was launched as a free, public genomic data repository and retrieval service devoted to genome-scale trichomonad data. The site currently contains all of the T. vaginalis sequence project data, several EST libraries, and tools for data mining and display. TrichDB is part of the NIH/NIAID-funded EupathDB functional genomics database project.[36]

Genetic diversity

Recent studies into the genetic diversity of T. vaginalis has shown that there are two distinct lineages of the parasite found worldwide; both lineages are represented evenly in field isolates. The two lineages differ in whether or not T. vaginalis virus (TVV) infection is present. TVV infection in T. vaginalis is clinically relevant in that, when present, TVV has an effect on parasite resistance to metronidazole, a first line drug treatment for human trichomoniasis.[37]

Increased susceptibility to HIV

The damage caused by T. vaginalis to the vaginal epithelium increases a woman's susceptibility to an HIV infection. In addition to inflammation, the parasite also causes lysis of epithelial cells and RBCs in the area leading to more inflammation and disruption of the protective barrier usually provided by the epithelium. Having T. vaginalis also may increase the chances of the infected woman transmitting HIV to her sexual partner(s).[38][39]

Evolution

The biology of T. vaginalis has implications for understanding the origin of sexual reproduction in eukaryotes. T. vaginalis is not known to undergo

Giardia lamblia (also called Giardia intestinalis), indicating that these meiotic genes were present in a common ancestor of T. vaginalis and G. intestinalis. Since these two species are descendants of lineages that are highly divergent among eukaryotes, and the meiotic genes were likely present in a common ancestor of all eukaryotes.[40]

See also

  • List of parasites (human)

References

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Further reading

External links
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