Pentatrichomonas hominis infection in rheumatoid arthritis treated with adalimumab

Sir, An increased risk of infection has been documented in patients with RA treated with biologics, especially TNF-α inhibitors (anti-TNF-α) [1]. Data on parasitic infections are scarce [1, 2]. Trichomonads are a group of flagellated protozoa. Four species infect humans: Trichomonas vaginalis, Trichomonas tenax, Dientamoeba fragilis and Pentatrichomonas hominis. Among these, only T. vaginalis is clearly pathogenic while the others exhibit a questionable pathogenicity [3]. P. hominis (formerly Trichomonas hominis or Trichomonas intestinalis) lives in the large intestine and cecum, where it is regarded as a commensal and is considered non-pathogenic [3]. Infection is usually asymptomatic in healthy and immunocompetent persons [3]. However, the pathogenicity of P. hominis is not widely accepted. Indeed, under certain unbalanced conditions in the digestive tract, this parasite is often identified in diarrhoeic stool [3, 4]. We provide the first report of a patient with a serious infection caused by P. hominis following adalimumab administration for RA. The patient consented to the publication of this article. A 68-year-old French Caucasian man presented to our emergency department with fever, mucous diarrhoea, tenesmus and arthralgia. This patient had been on holiday in Burkina Faso for 8 days. His medical history was significant for cardiac arrhythmia treated with amiodarone and fluindione and RA treated with prednisone (10 mg/day), SSZ (2 g/day) and adalimumab (40 mg/2 weeks for ∼3 years). At the request of his rheumatologist, the patient received two doses of adalimumab at an interval of 1 week in order not to receive any injections in Africa during his holiday. The patient’s vital signs were stable except for a temperature of 39.8°C (103.64°F). His physical examination was remarkable for abdominal pain in the lower quadrants and active RA (DAS28 = 4.43). The remainder of the physical examination was unremarkable. His complete blood cell count and basic metabolic panel were within normal limits, except for a white blood cell count of 17 600/mm3 (neutrophils 83%). CRP was 96 mg/l. Infectious disease testing (thick blood smears, Widal test, culture of blood, urine and stool) were globally negative. Stool specimens were only positive for trophozoites of P. hominis. As this parasite is considered non-pathogenic, there are no treatment recommendations. However, imidazole derivatives may be effective [5]. The patient was treated with infusion of metronidazole 1500 mg/day, associated with symptomatic measures. The outcome was favourable in 2 days, with the disappearance of gastrointestinal symptoms and an improvement in joint symptoms (DAS28 = 2.59; CRP = 12). Although a pathogenic impact of P. hominis is still discussed, it is known that this flagellate is the causative organism of abnormalities of the digestive tract like diarrhoea, dysentery-like disturbance, colitis, appendicitis and subhepatic abscess, but also empyema [4, 6, 7]. Our case report is unique in more ways than one. First, it provides new insight into the potentially pathogenic nature of P. hominis, especially when no other microbe is identified. However, controversy persists, with data in the literature that emphasize the non-pathogenic nature of this protozoan [3, 8], even in immunocompromised patients [8]. Like other flagellates, faecal–oral transmission of P. hominis involves the ingestion of contaminated food or water. The prevalence of this parasite is very low in developed countries [3], while it is higher (up to 39%) in subtropical and tropical zones [9]. However, because of the incubation period, we could not say absolutely if infection took place in Burkina Faso or France. Secondly, our observation lengthens the list of parasitoses that may occur during anti-TNF-α treatment, foremost of which is leishmaniasis [1]. As in our patient, these parasitic infections can be serious and require hospitalization [1, 10]. Thirdly, the immunosuppression associated with high-dose adalimumab could partly explain the pathogenicity of P. hominis. Otherwise, and newly found, higher disease activity is associated with a higher probability of developing infections. Indeed, each 0.6 U increase in DAS28 score corresponded to a 4% increased rate of outpatient infections and a 25% increased rate of infections requiring hospitalization [10]. However, the relationship between immunosuppression and P. hominis is not clearly established. Although extra-digestive involvement occurs in immunocompromised patients [6], cases in immunocompetent patients are also described [7]. To the best of our knowledge, this is the first documented case of infection caused by P. hominis in a patient with RA treated with adalimumab. Parasites considered non-pathogenic can cause serious infection, especially in patients treated with anti-TNF-α travelling in tropical areas. Prescription rules of biologics must be respected. Disclosure statement: The authors have declared no conflicts of interest.