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Trichomoniasis is a sexually transmitted protozoal disease that occurs worldwide in both males and females. The infection, which can also be called vaginitis (in females) or urethritis (in males), is usually mild or covert in occurrence, and infants can become infected with the disease during delivery (if the mother is already infected). Though trichomoniasis usually occurs with or without symptoms, the infection is typically symptomatic in females where the vagina is affected. But in males, trichomoniasis is asymptomatic or mild, and this can result in painful urination in affected individuals. Females infected with Trichomonas vaginalis usually show a characteristic purulent discharge from the vagina. Sexual intercourse is the major route or means via which the disease can be transmitted in human population, though infant infection during childbirth has been reported.

Trichomoniasis is caused by flagellated protozoa in the genus Trichomonas. The species of Trichomonas include:

  1. Trichomonas vaginalis
  2. Trichomonas tenax
  3. Trichomonas hominis (Pentatrichomonas hominis)
  4. Dientamoeba fragilis

T. vaginalis is the only medically important species in the group because it is responsible for causing trichomoniasis in females (vaginitis) and males (urethritis). Other species of Trichomonas are of less clinical significance because they are not known to cause infections in humans.

Type and morphology of Trichomonas

Trichomonas vaginalis is a flagellated protozoan that exists as trophozoites in the body of infected human hosts. It is found in the Class Mastigophora alongside Giardia, Trypanosoma and Leishmania. The trophozoite is the only known existing form of T. vaginalis. T. vaginalis is fitted with four anterior flagella which provide movement for the organism, thus the trophozoite forms of T. vaginalis is motile. The trophozoite also has a fold of cytoplasm and an undulating membrane which runs along one side of the parasites body. The parasite is pear-shaped in structure, and it measures about 10-15 X 8-10 µm in length. All species of Trichomonas are morphologically identical when alive. The motile trophozoite forms of T. vaginalis exhibit an amoebic type of movement.  This type of movement is called wobbling or rotational movement. Characteristically, T. vaginalis and other Trichomonas species posse an organelle called hydrogenosomes which helps them to generate their own energy (i.e. adenosine triphosphate, ATP molecules). Cyst forms of T. vaginalis do not exist but only the trophozoite forms.        

Vector, reservoir and habitat of Trichomonas

T. vaginalis has no intermediate host. Humans are the only definitive host of the parasite. T. vaginalis is not transmitted to humans via insect vector or rodent as is the case in other parasitic infections. Sexual intercourse with an infected person is the chief route of transmitting and acquiring the infection. T. vaginalis is a vaginal protozoan that causes sexually transmitted vaginitis in women and urethritis in men. The use of contaminated or infected towels, sponges and other medical equipments including sitting on contaminated toilet sits have also been implicated as alternative medium via which the disease can spread in the population. Nevertheless, direct body contact through sexual intercourse is the primary means of contracting the parasite since T. vaginalis does not have cyst forms.

Clinical signs and symptoms of Trichomonas infection

The clinical signs of trichomoniasis include profuse yellowish discharge from the vagina, vulvovaginal soreness and irritation or burning sensation of the vagina, reddening and tenderness of the vagina, itching at the vagina area and offensive odour. T. vaginalis infection also raises the pH of the vagina above the normal level (4.5). Menstruation also worsens the signs and symptoms of the disease. Though males generally experience very mild or covert infection, the signs and symptoms of T. vaginalis infection in males may include infection of the seminal vesicles, urethra and prostate gland. Some males can also experience burning sensation during urination. T. vaginalis does not exhibit or have a life cycle like other protozoa because the parasite is known to exhibit in only one form, which are the motile trophozoite forms. 

Pathogenesis of Trichomonas infection

Trichomoniasis is an exclusively sexually acquired infection, thus the infection can be likened to be a sexually transmitted infection (STI) that is of parasitic origin. T. vaginalis thriveswith a fluctuating pH level of the female vagina. The normal pH level of a female vagina is between 3.8-4.4, a physiological condition of the vagina that defends against pathogen invasion including T. vaginalis. Trichomoniasis can progress from an asymptomatic infection to a symptomatic inflammatory disease with offensive purulent discharge from the vagina. But in males, the urethra is the most commonly affected site. T. vaginalis is usually localized around the lower urogenital tract, and progression of the disease away from this region to the upper urogenital tract of both men and women is rare and has not been established. Following infection with T. vaginalis after sexual intercourse with an infected person, white blood cells or polymorphonuclear leukocytes will be recruited in large amount at the site of the infection (Figure 1).

Migration of polymorphonuclear leukocytes to the site of infection with T. vaginalis results in the inflammation of the affected area which can be the vagina or urethra in women and males respectively. There is profuse purulent discharge from the female vagina and possibly irritation or burning in males during urination. Though a non-ulcerating infection, T. vaginalis infection has been implicated in increasing the chances of HIV transmission in heterosexual intercourse just as is the case with other STIs including gonorrhea. T. vaginalis infection is chronic in females, and the infection is restricted to the cervix, vagina and vulva regions of the body. In males, the prostate and epididymis may be affected. The cidal action of prostate gland secretions makes T. vaginalis infections in this organ to be less sever and mild than in the urethra in males. The high levels of zinc present in prostatic secretions in males coupled with the preference of the parasite for squamous epithelium in females prevents the multiplication and dissemination of T. vaginalis beyond the lower urogenital tract.

Figure 1. Life cycle of Trichomonas vaginalis infection. CDC

Laboratory diagnosis of Trichomonas infection

T. vaginalis infection (vaginosis or urethritis) is diagnosed in the laboratory by requesting for a vaginal discharge specimen from infected female patients. Semen, urine or urethral secretions or swabs are requested from infected male patients. Wet film examination of any of these specimens under the microscope is still the principal way of diagnosing trichomoniasis in the laboratory. Clinical specimens are examined without delay after collection to investigate and demonstrate the motile forms of T. vaginalis (i.e. the trophozoites) which is the number one evidence for the presence of an actual infection. The undulating membrane and the flagella of the organism should be looked out for upon examination of clinical specimens. Other methods used for diagnosing trichomoniasis in the laboratory include serological investigations, culture, PCR tests and DNA probing tests. However, microscopical examination of specimens (i.e. wet-film examination) still remains the most effective and dependable tool for diagnosing possible T. vaginalis infection.

Treatment of Trichomonas infection

Trichomoniasis is treated with topical and systemic chemotherapeutic agents including metronidazole, clotrimazole, acetarsol, and tinidazole. Infected patient’s partner should also be examined and treated alongside their infected partner in order to prevent re-infection. Sex should also be discontinued as much as possible during the periods of treatment. Proper protection must be followed if infected partners must indulge in sexual activity in the course of therapy. The effective treatment of sexual contacts of both partners involved is necessary to prevent the re-infection of the disease in the individuals. While systemic chemotherapeutic agents such as metronidazole are used orally, topical agents including acetarsol and clotrimazole are applied at the vaginal region to ease infection and to restore the normal pH of the vagina which is very necessary to hold off invading pathogens. Patient’s compliance to their treatment regimens is critical to improving their health status as well.   

Control and prevention of Trichomonas infection

T. vaginalis infection accounts for one of the most widespread non-viral, non-bacterial STIs that affects over 100 million people worldwide. Though the infection occurs worldwide, trichomoniasis is more prevalent in the developing nations and other poor regions of the world. In countries were trichomoniasis are more common, infections amongst females have been discovered to surpass infection in males, and intimate sexual intercourse with infected individuals has been implicated as the underlying principle that perpetuates the spread and transmission of T. vaginalis infection in human population. Due to this development, a behavioural change in people’s sexual lifestyles is critical to controlling and preventing the spread of the disease. Because trichomoniasis may increase the chances of people contracting HIV, sexual intercourse should be done with caution and protection. Infected individuals should seek medical care, and quality and inexpensive healthcare should be made available in T. vaginalis endemic regions as support to slowdown the transmission of HIV and trichomoniasis in particular.   


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