Transmission of Entamoeba nuttalli and Trichuris trichiura from Nonhuman Primates to Humans

To the Editor: Entamoeba nuttalli parasites are frequently found in fecal samples of nonhuman primates (NHPs) in zoos (1). This gastrointestinal pathogen is the causative agent of invasive amebiasis in NHPs, which may result in hemorrhagic dysentery, liver abscess or other extraintestinal pathologies, and even death (2). E. histolytica infection is the cause of invasive amebiasis in humans and can also cause experimentally invasive amebiasis in NHPs (3). The host specificity of E. nuttalli and E. histolytica parasites remains largely unknown. Although molecular analyses indicate that E. nuttalli parasites are genetically different from E. histolytica parasites (4), and hence provide a unique marker to identify zoonotic transmission, molecular tools have not been applied extensively to determine the presence of E. nuttalli in humans (5). Moreover, studies suggesting transmission have been based on clinical outbreaks in animal caretakers (2), and because infections may not always be symptomatic, the results of those studies may underestimate the incidence.

We conducted a study to assess the occurrence of zoonotic transmission of E. nuttalli and other gastrointestinal parasites in animal caretakers in 5 zoos in Belgium and the Netherlands. A previous cross-sectional survey (6) in these zoos indicated that >80% of the 67 groups of NHPs (40 species, 400 animals, and 1,435 samples) were infected with at least 1 of the 13 gastrointestinal parasites found. In that survey, the most frequently detected parasites were E. nuttalli (found in 7 [10.4%] of the 67 groups of NHPs), Trichuris trichiura (12 [17.9%]), Balantidium coli (14 [20.9%]), and Giardia duodenalis (26 [38.8%]). These parasites can cause clinical symptoms in animals and humans. In our study, caretakers of NHPs in each zoo were screened on a voluntary basis for gastrointestinal parasites; animals other than NHPs were also screened (control group). Fecal samples were processed by the acid-ether concentration method and then examined by microscopy to identify the presence of protozoan cysts and helminth eggs (6). With the exception of fecal samples from 13 caretakers at 2 zoos, all samples were also processed by using real-time PCR to ascertain the presence of E. nuttall, E. histolytica, and E. dispar parasites (7). E. nuttalli can only be detected by PCR targeting the E. histolytica–specific repeat; the parasite cannot be detected by a PCR based on the ribosomal small subunit of E. histolytica. Both PCRs amplified E. histolytica (8). Fisher exact test was applied to determine whether there was a difference in parasite infection, as determined by microscopy, between caretakers responsible for NHPs and those caring for animals other than NHPs. An independent physician gave medication to caretakers who were infected with parasites. The study protocol was approved by the Ethics Committee of Ghent University (Belgium; no. 2008/359), Antwerp University (Belgium; no. UA A08 21), and Leiden University Medical Center (the Netherlands; no. 26734).

Fifty-four animal caretakers from 5 zoos participated in the survey; 42 of the caretakers were responsible for NHPs and 12 for animals other than NHPs. Microscopy and PCR results showed that 16 (29.6%) caretakers were infected with >1 parasite. We used microscopy to detect cysts of various Entamoeba species in fecal samples from 13 (24.1%) caretakers; samples from 4 (7.4%) caretakers were positive for T. trichiura eggs. Infections with Entamoeba species and T. trichiura were observed only in caretakers of NHPs, suggesting that these caretakers are at higher risk of acquiring parasitic infections (p = 0.03). PCR detected E. nuttalli, E. histolytica, and E. dispar parasites in 1, 1, and 3 of 41 caretakers, respectively. We were not able to perform PCR on all fecal samples from 2 zoos (13 caretakers). E. nuttalli parasites were detected in a caretaker working in a zoo where E. nuttalli infections were prevalent in animals. E. histolytica parasites was detected in a caretaker employed in a zoo where E. nuttalli infections were not detected in animals. All T. trichiura infections were detected in caretakers from 1 zoo, and T. trichiura infections were also prevalent in that zoo’s animals. None of the caretakers reported gastrointestinal problems.

The presence of E. nuttalli and T. trichiura parasites in caretakers in zoos where these parasites are also prevalent in NHPs strongly suggests NHP-to-human transmission of these parasites, as was reported for Blastocystis parasites (9). Genotyping of E. nuttalli isolates from NHPs and animal caretakers could be performed for additional confirmation of NHP-to-human transmission of E. nuttalli parasites (10). The E. nuttalli–infected caretaker in this study appeared to be completely asymptomatic. Although E. nuttalli parasites are as virulent as E. histolytica parasites in animal models, it remains unclear whether they are as virulent in humans (4). We recommend that caretakers of NHPs be screened on a regular basis and be provided with appropriate medications if needed.