Introduction

Trichomonas vaginalis is a flagellated protozoan parasite of the human genital tract, which is responsible for one of the most common sexually transmitted infections (STI), trichomoniasis. According to the World Health Organization (WHO), it was estimated that in 2016 there were 156 million new cases in women and men aged 15-49 years, worldwide.¹ However, the exact prevalence of trichomoniasis is probably underestimated.

Clinically, T. vaginalis infection of the female genital tract includes vaginitis, cervicitis, and pelvic inflammatory disease. In men, it is asymptomatic in up to 75% of cases, but transient and mild urethritis, epididymitis, or prostatitis can occur.²

Apart from the generally mild nature of trichomoniasis, growing evidence shows that T. vaginalis infection is associated with more serious conditions, such as prostate^3,4and cervical cancer,⁵ adverse pregnancy outcomes,⁶ and infertility.⁷ Furthermore, several studies support an epidemiological linkage between human immunodeficiency virus (HIV) and T. vaginalis, suggesting that T. vaginalis infection represents a significant risk factor in the sexual transmission of HIV, increasing the likelihood of its acquisition by 50%.⁸ Consequently, growing attention to the diagnosis and treatment of patients infected with T. vaginalis has emerged in recent years.

Although screening for T. vaginalis is not yet routinely recommended, new advances in testing for STIs have also increased diagnostic opportunities for this infection.

Herein, we describe the case of a man with urethritis caused by T. vaginalis.

Discussion

Trichomonas vaginalis has been increasingly recognized as a pathogen of the male genitourinary tract. According to the literature, this parasite is responsible for 1%-20% of nongonococcal urethritis.⁹ However, its exact prevalence is probably higher than documented due to several reasons.

First of all, trichomoniasis is not a notifiable STI in many countries, such as Portugal. The most recent WHO assessment from data collected in 2016 revealed an incidence of 156 million cases worldwide. It corresponds to more numerous new infections by T. vaginalis than the well-documented STIs, such as Chlamydia trachomatis infection and gonorrhea, which have an estimated global incidence of 127.2 million and 86.9 million, respectively. Moreover, the prevalence and incidence of trichomoniasis are geographically variable, with the highest prevalence found in Africa (11.7% of females, 1.2% of males), and in the Americas (7.7% of females, 1.3% of males).¹

Secondly, T. vaginalis infection may be asymptomatic for a long period among men and women. Therefore, the absence of recent sexual history should not be used to rule out T. vaginalis infection as a possible diagnosis.² Nevertheless, comprehensive guidelines for T. vaginalis testing are lacking. At most, its screening has been suggested only in populations where the prevalence of infection is considered high (>2% in symptomatic women).⁹

Thirdly, different from females, who frequently present vaginitis, cervicitis, including the typical inflamed and speckled “strawberry cervix”, and pelvic inflammatory disease, men are mostly asymptomatic or exhibit transient symptoms of mild urethritis, epididymitis, or prostatitis. This might explain why the estimated prevalence of T. vaginalis infection in men is 10 times lower than in women.² Until recently, little importance had been given to the impact of T. vaginalis infection in men, since it was believed that it had no serious consequences for their health. However, the recent observation that T. vaginalis seropositivity is associated with the development of prostate cancer³ has raised concern. Furthermore, it has been demonstrated that T. vaginalis enhances the transmission of sexually transmitted microorganisms, such as HIV, which makes the control of this parasite a critical issue in both men and women.⁸

Lastly, another aspect that has possibly contributed to the under-recognition of T. vaginalis infection is the low sensitivity of the diagnostic tests traditionally used. The wet-mount microscopy is a simple, fast, and cost-effective method, with a sensitivity of around 60%.^2,10, it requires a short time between the sample acquisition and observation (10 minutes),¹¹ due to the reduction of the parasite’s motility with time, essential for its identification. However, it is highly operator-dependent and is unlikely to detect low-level infections, in which the organism load in the sample is below 10⁴ cells/mL.¹²This limitation is especially relevant for male T. vaginalis infection, as male urethral and urinary specimens generally present a low organism burden.² Therefore, culture has been the gold standard in the diagnosis of T. vaginalis infection. However, despite having a slightly higher diagnostic sensitivity than wet-mount microscopy, the one-week incubation required to obtain results is a major inconvenience of this method.^2,10,12The advent of highly sensitive and specific molecular diagnostic tests has provided new critical tools for the diagnosis of STIs, including trichomoniasis. There are currently six molecular tests approved by FDA for diagnosing trichomoniasis in women, but only one is validated for the diagnosis of trichomoniasis in men.¹³

At present, the Centers for Disease Control and Prevention (CDC) and International Union against Sexually Transmitted Infections (IUSTI) guidelines recommend molecular detection methods to diagnose trichomoniasis, including several validated nucleic acid amplification tests (NAATs).^9,11,15

Accurate diagnosis of trichomoniasis is of most importance for the subsequent treatment of T. vaginalis infection, as antibiotics given for general urethritis treatment such as azithromycin or doxycycline are not effective for trichomoniasis. According to the CDC and IUSTI guidelines, the recommended treatment for T. vaginalis infection is an oral nitroimidazole (metronidazole or tinidazole). Possible treatment schemes are a single 2 g dose of metronidazole, a single 2 g dose of tinidazole, or 500 mg of metronidazole twice daily for 7 days.^11,15Metronidazole gel is not recommended.¹¹ Some degree of resistance to nitroimidazoles may occur in a small percentage of cases (less than 10% for metronidazole), being overcome with higher doses and longer courses of these medications. In women, concomitant treatment with intravaginal tinidazole twice daily or intravaginal paromomycin daily for 14 days may be indicated in cases of nitroimidazole resistance.¹⁶ Treatment should be instituted immediately after diagnosis. Concomitant treatment of sexual partners should also be applied. Patients should be advised not to take alcohol for the duration of treatment and at least during the next 48 hours (72 hours for tinidazole).¹¹ Abstinence of sexual activity until pharmacological treatment completion and symptom resolution should be indicated.^11,15Considering the high rate of coinfection with other STIs, their screening should be performed. Rescreening for T. vaginalis infection is advisable by the CDC for sexually active women at three months post-therapy. However, no data are available on rescreening men.¹⁵ Preventive measures, such as male condom use, should be encouraged.¹⁷

In conclusion, the relevance of male T. vaginalis infection has probably been underappreciated, since it was believed to be a self-limited condition, without serious consequences. However, recent findings have shown that, as in women, trichomoniasis can also affect male health. The association between T. vaginalis infection and prostate cancer, HIV infection, and other STIs highlighted the pertinence of its recognition and prompt treatment in the male population. The recent emergence and validation of highly sensitive and specific molecular diagnostic tests have allowed a greater opportunity for the detection of this parasite, especially in men, as diagnosis through traditional methods is much more challenging.