Life Cycle and Transmission

In 1883 Kustler redescribed the structure of T. vaginalis: the split flagellum described by Donne was in reality 4 flagella, the cilia were an undulating membrane, and the pointed end was the rod-shaped axostyle. Using stains, in conjunction with light and electron microscopy, it is now possible to give a more detailed description of T. vaginalis: the  size and shape are  variable with the average length being 10mm and the width 7 mm (FIGURES 1 and 2). Unattached its shape tends to be

 

heart-shaped or oval, but when attached to the vaginal epithelium it is more ameboid. T. vaginalis has 5 flagella, four of which are located anteriorly, and the fifth is incorporated within the undulating membrane. The undulating membrane is supported by a structural element, the costa. The beating of the flagella together with the undulating membrane produces a quivering swimming motion. Within the cytoplasm is a single nucleus, and several cytoskeletal elements: the pelta which consists of bundles of microtubules which support anterior part of body and shapes the periflagellar canal, and the rodlike axostyle (which begins at the nucleus and protrudes through the posterior tapering to a sharp point) serves to anchor the parasite to the vaginal epithelial cells. There is a blepharoplast complex consisting of flagellar basal bodies (kinetosomes), a Golgi apparatus called the parabasal body, many glycogen granules, free and membrane-bound ribosomes, and unique membrane bound-organelles, called hydrogenosomes. There are no mitochondria. T. vaginalis produces no cysts and divides by longitudinal binary fission without the disappearance of the nuclear membrane. Feeding is by phagocytosis and/or pinocytosis.

(http://medlib.med.utah.edu/parasitology/tvagim.html) 

Humans are the only natural host for T. vaginalis and the trophozoite is transmitted directly from one person to another usually by sexual intercourse. The evidence that T. vaginalis is a STD (sexually transmitted disease) is based on the following evidence:

1. there is a high rate of infection in male partners of infected females,

2. recurrent trichomoniasis in a female is cured after eradication of the male partner’s infection,

3. the frequent occurrence (56%) of trichomonisis in females attending STD clinics, and

4. the higher incidence of trichomoniasis in prostitutes than in postmenopausal women and virgins.

 

Since Trichomonas lacks a cyst, and the flagellate dies outside the human body unless protected against drying,  a moist environment is critical for transmission to occur. Indeed, Trichomonas can survive 1-2 days in urine and 2-3 hours on a wet sponge.  Non-sexual transmission has been documented when contamination occurs with douche nozzles, specula, toilet seats, and moist towels. However, such cases of transmission are rare. Two-17% of newborn infants of mothers infected with T. vaginalis have acquired trichomoniasis when the parasites moved into the neonate’s urinary or vaginal tract.