Trichomoniasis Case File

Trichomoniasis Case File

Eugene C.Toy, MD, Cynthia Debord, PHD, Audrey Wanger, PHD, Gilbert Castro, PHD, James D. Kettering, PHD, Donald Briscoe, MD

CASE 50

A 19-year-old woman presents to the physician’s office for the evaluation of an itchy vaginal discharge that she has had for about a week. She has had no fever, abdominal pain, or dysuria. She became involved with a new sexual partner approximately 3 weeks ago. She takes birth control pills but does not regularly use condoms during intercourse. Her partner is asymptomatic. On examination, her vital signs are normal, and a general physical examination is unremarkable. On pelvic examination, her external genitalia are normal. After inserting a speculum you see a bubbly, thin, yellow vaginal discharge. Her cervix is erythematous but without discharge. She has no cervical motion or uterine or adnexal tenderness. A wet mount of the vaginal discharge examined microscopically reveals numerous motile, flagellated, pear-shaped organisms along with numerous white blood cells.

◆ What is the most likely infectious cause of her vaginal discharge?

◆ What is the most likely source of her infection?

ANSWERS TO CASE 50: TRICHOMONIASIS

Summary: A 19-year-old woman with vaginal discharge, which on microscopy reveals numerous motile, flagellated, pear-shaped organisms along with numerous white blood cells.

◆ Most likely infectious cause of her vaginal discharge: Trichomonas vaginalis

◆ Most likely source of her infection: Sexual contact with infected but asymptomatic partner

CLINICAL CORRELATION

Trichomonas vaginalis is a motile, pear-shaped protozoan with four flagella and an undulating membrane. It multiplies by binary fission and exists only in its trophozoite form; no cyst form has been identified. It is a common cause of both symptomatic and asymptomatic infections. Many infected women are asymptomatic or have only a small amount of thin vaginal discharge. Others develop symptomatic disease with vaginal inflammation, itching, and copious vaginal discharge. The discharge may be white, yellow, or green, and bubbles are often seen. Cervical inflammation with punctate hemorrhages may produce a “strawberry cervix.” The vast majority of infections in men are asymptomatic, although urethritis, prostatitis, and epididymitis can occur. The parasite is almost always passed by sexual contact, although fomite transmission has been documented. The diagnosis is most often made by the microscopic evaluation of a sample of vaginal discharge in a saline wet mount. Flagellated, motile trichomonads will be visible in most symptomatic infections. The diagnosis can also be made by the identification of organisms on Pap smears, by culture of the vaginal discharge, or by the use of specific monoclonal antibody stains or nucleic acid probes. This infection is usually treated with oral metronidazole, and both partners should be treated to prevent reinfection. Because of its route of transmission, the identification of infection with Trichomonas should prompt the consideration of evaluation for other sexually transmitted diseases.

APPROACH TO THE SUSPECTED Trichomonas INFECTION

Objectives

1. Learn the life cycle of Trichomonas vaginalis and the epidemiology and clinical course of infection.

2. Be able to answer the three basic aspects of infection: transmission, diagnosis, and treatment/prevention.

Definitions

Trophozoite: Feeding stage of protozoans, in contrast to the vegetative cyst stage that may be present in the life cycles of some protozoa.

Axostyle: A hyaline rod-like structure that runs through the length of T. vaginalis and exits at the posterior end.

Fomite: A substance other than food that may harbor and transmit infectious agents.

DISCUSSION

Characteristics of Trichomonas That Impact Transmission

The life cycle of trichomonads in general is the simplest of protozoan life cycle because the organism exists only as a trophozoite that divides by binary fission. Transmission is presumed to be by direct transfer of trophozoites because a cyst stage does not exist.

Sexual intercourse is considered the usual means of transmitting this infection that is common worldwide. The organism is transmitted cyclically from a woman to a man and back to the same or another woman. Infected men, who play a key role in transmission, are usually asymptomatic. Trichomonas vaginalis trophozoites in vaginal discharge are known to live for 30 minutes or more on toilet seats, supporting the possibility that some infections could be acquired through fomites such as towels and toilet seats. However, this means of transmission is not well supported by evidence.

Diagnosis

If infection with T. vaginalis is suspected, a first step is to diagnose infection by microscopically examining a wet mount preparation of vaginal discharge from the patient. The live parasite appears as a pear-shaped trophozoite with active flagella that give it motility. Sometime the undulating membrane provides a waving movement. Propagation and concentration of the organism in culture is a possibility if wet mounts are negative. However, examination of wet mounts is usually sufficient to find and identify the organism.

Treatment and Prevention

Metronidazole is effective in treating T. vaginalis. Treatment of both sexual partners is recommended to prevent reinfection. Using condoms correctly and consistently will lower the risk of individuals contracting trichomoniasis and other sexually transmitted diseases.

Synopsis

The synopsis of vaginal trichomoniasis is presented in Table 50-1.

Table 50-1

COMPREHENSION QUESTIONS

[50.1] Trichomoniasis is transmitted by which stage?

A. Cyst

B. Oocyst

C. Egg

D. Sporozoite

E. Trophozoite

[50.2] What is the drug of choice in treating vaginal trichomoniasis?

A. Metronidazole

B. Mebendazole

C. Mefloquine

D. Niclosamide

E. Niridazole

[50.3] Laboratory diagnosis of vaginal trichomoniasis is most commonly made by which of the following methods?

A. Identifying cyst stages in an iodine stained preparation of vaginal secretion.

B. Finding trophozoites in a saline wet mount of vaginal discharge.

C. Using an acid-fast stain to highlight the parasite.

D. Staining a thin blood smear with common blood stains.

E. Testing for specific antibodies against T. vaginalis in the patient’s serum.

Answers

[50.1] E. Trichomonas vaginalis exists only as a trophozoite; no cyst stage has been identified. A cyst (A), oocyst (B) and sporozoite (D) are stages involved in transmitting other protozoan infections, and an egg (C) is the means of transmission in a number of helminth infections.

[50.2] A. Metronidazole is the drug of choice. Mebendazole (B) is a broadspectrum antinematode agent. Mefloquine (C) is used as a prophylactic drug to prevent malaria and also used to treat chloroquine-resistant clinical malaria. Niclosamide is a broad-spectrum agent effective in the treatment of adult tapeworm infections. Niridazole (E) is a drug used to treat schistosomiasis if praziquantel is not available.

[50.3] B. Trophozoites are usually visible in saline mounts of vaginal discharge or scrapings. Cysts (A) are not present in the T. vaginalis life cycle, and iodine is used primarily to observe cysts of intestinal protozoa. Acid-fast stains (D) are used to search for oocysts of coccidian intestinal parasites, such as Cryptosporidium and Cyclospora. Thin blood smears are used to diagnose malaria. Serologic diagnoses (E) are helpful in the diagnosis of several “deep tissue” parasites but are not used in diagnosing T. vaginalis.

MICROBIOLOGY PEARLS ❖ Trichomonas vaginalis is an important sexually transmitted parasite throughout the world. ❖ Only trophozoite stages occur and frequently are difficult to find in a saline wet mount. ❖ Males and females are host, although males are generally asymptomatic. ❖ Metronidazole is the drug of choice for treating trichomoniasis.

REFERENCES

Centers for Disease Control. DPDx. Laboratory identification of parasites of public concern. Trichomoniasis. 2007. http://www.dpd.cdc.gov/dpdx/HTML/ Trichomoniasis.htm. 

Centers for Disease Control. DPDx. Laboratory identification of parasites of public concern. Image Library. Trichomoniasis. 2007. http:www.dpd.cdc.gov/dpdx/ HTML/ImageLibrary/Trichomoniasis_il.htm. 

Medical Letter on Drugs and Therapeutics. Drugs for parasitic infections. New Rochelle, NY. 2004. http://www.medletter.com/freedocs/parasitic.pdf. This reference has been updated and “superseded by the special report Drugs for Parasitic Infections, which can be purchased (on-line) for $25.” This reference has been provided because it is a comprehensive and clinically useful reference that is regularly updated and could be of value to those who are involved in treating parasitic infections.

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