Trichomonas vaginalis

                           Trichomonas vaginalis

History:

¢ First observed by Donne in 1836 in vaginal secretions.

Habitat:

¢ Inhabit

-         Female: vagina and urethra

-         Male: prostate gland, seminal vesicles and   urethra.

Morphology

¢ Exist only as trophozoites and

     is infective form of parasite.

¢ Cyst form absent.

¢ Trophozoites:

-         Shape: ovoid or pear-shaped.

-         Size: 7-23µm in length and   6-8µm wide.

-         Short undulating membrane reaching upto the middle of the body.

-         Single nucleus, located in the anterior portion .

-         Prominent axostyle that runs throughout the length of  the body and projects posteriorly.

-         Presence of five flagella, impart charcteristic motility known as wobbling or rotatory movement.

-         Four anterior  free flagella, arising from a shallow depression in the anterior end of the body called periflagellar canal.

-         Fifth flagellum curves back along the margin of the undulating membrane and is called the recurrent flagellum.

-         Not enclosed by undulating membrane but lies in a shallow groove in the free margin of the membrane.

-         Just beneath the membrane lies the costa, a unique rigid cord, filamentous in appearance that supports undulating membrane.

-         Cytoplasm contains large numbers of chromatin granules around costa and axostyle.

-         Simple, completed in a single host either male or female.

-         Infection transmitted sexually from a women acting as a reservior of infection to man.

-         In female, parasite gets nourishment from the mucosal surface of the vagina, and from the ingested bacteria and erythrocytes.

-         Reproduce by longitudinal binary fission, begins by division of nucleus, followed by division of neuromotor apparatus and finally separation of cytoplasm into two daughter trophozoites.

-         Trophozoites are infective stages.

-         On sexual contact, trophozoites transmitted to male and localise in the urethra and prostate gland.

-         These trophozoites under go replication in the same way as in vagina of female.

Pathogenesis

¢ Non invasive parasite, remains adherent to the mucosal epithelium of the vagina or urethra and causes superficial lesions. Infects squamous epithelium but not columnar epithelium.

¢ Virulence factor:

-         Protein liquids and Proteases- helps in adherence of trophozoites to epithelial cells of the genito-urinary tract.

-         Enzyme cysteine protease- responsible for haemolytic activity.

-         Normally,vaginal epithelial surface is rich in glycogen and lactobacillus. Lactobacillus converts glycogen to lactic acid that maintains acidic pH of vagina.

-         Parasite feed on host vaginal cells, results in disruption of the glycogen levels and vaginal bacterial flora leading to rise in pH level. The parasite thrives at pH levels that exceed 4.9.

-         May occur epithelial erosion which lead to petechial haemorrhage and metaplastic changes in the epithelium.

Clinical disease

¢ Incubation period- ranges from 4-28 days.

¢ Cause trichomoniasis.

¢ In women,

-         altered vaginal environment is common, have a scant, watery vaginal discharge.

-          Vaginitis may occur, with symptoms like itching, burning and painful urination along with profuse, forthy and malodorous discharge containg bacteria, pus and trophozoites.

-         PID most important complication.

-         Pregnant women infected with T.vaginalis , more likely to have premature rupture of membranes, premature birth and pre-term or low birth weight baby.

¢ In men,

-         infections are usually asymptomatic.

-         Occasionally experience urethritis, prostatitis and cystitis.

-         May occur infertility.

¢ Both in male and female, infection is associated with gonorrhoea, chlamydia, and HIV infections.

Laboratory diagnosis

¢ Specimen: vaginal and urethral discharges, prostatic secretion, endocervical specimens or urine sediments.

¢ Microscopy:

-         Direct wet mount: a small amont of freshly collected specimen is mixed with a drop of saline on a microscope slide and covered with a coverslip. Examine under low power for presence of actively motile trophozoites. If motility diminishes, it may be possible to observe movement of undulating membrane, under high dry power.

-         Staining: stained (giemsa, papanicolaou) preparetion of dry smear may be examined, but oragnisms may be difficult to recognise.

¢ Culture:

-         More sensitive than wet mount (93% sensitivity), but not routinely used as it is expensive and somewhat technically difficult.

-         Variety of media like

Ø Bushley’s, Feinberg-Whittington, Roiron’s and Johnson-Trussel etc can be used.

Ø CPLM (Cysteine peptone liver maltose) medium is frequently employed.

Ø Plastic envelope medium is also used and its sensitivity is reported to be superior to other available techniques.

¢ Other methods:

a)     Serological test: indirect haemagglutination and gel diffusion test are used for antibody detection.

b)    Gene probes: monoclonal antibodies and DNA probes are also effective.

c)     PCR: also used nowadays. 

Treatment

¢ Metronidazole (200-250 mg orally thrice daily for 5-7 days)

¢ To prevent recurrence, patient’s sexual partner should be tested and trated.

¢ Strains resistant to metronidazole is treated with tinidazole.

¢ During pregnancy, topical therapy with clotrimazole, in a dose of 100mg daily for 6 days is effective.