Dientamoeba fragilis is a protozoan that has been neglected in human and animal studies, even though it has been more than 100 years since its description. It is almost impossible to detect the parasite in direct microscopic examinations. Furthermore, detection in stained preparations is also not easy even when assessed by experienced laboratory workers. Therefore, molecular methods are currently accepted as the gold standard for diagnosing D. fragilis (McHardy et al. 2014; Röser et al. 2013; Verweij et al. 2007). In studies comparing the specificities and sensitivities of different diagnostic methods in detecting D. fragilis, molecular methods seem much more sensitive than direct microscopy, stained preparation examination, and culture methods (David É et al. 2015; Sarafraz et al. 2013; Yıldız et al. 2021). However, molecular methods are still not widely used in diagnosing this parasite since D. fragilis is frequently overlooked and molecular methods have a high cost compared to microscopic examinations. Hence, the reported D. fragilis detection rates often do not reflect the real-world status.
Almost all molecular data regarding the detection rates and characteristics of D. fragilis are obtained from scientific studies in humans (Bruijnesteijn van Coppenraet et al. 2009; Menéndez et al. 2019; Stark et al. 2014). Studies in animals are exceedingly rare even in comparison to human studies which are also insufficient. Thus, the zoonotic features of the parasite have not been clarified, and epidemiological data contain serious deficiencies. In addition, available data on the natural hosts of the parasite are minimal. Especially after the initial imaging of the cyst form of the parasite in 2013, a consensus emerged that the transmission route of D. fragilis was fecal-oral. This issue has made it more important to investigate the possible natural hosts and zoonotic characteristics of the parasite (Chan et al. 2016; Munasinghe et al. 2013). In this context, although there are few studies investigating D. fragilis in animals, this issue has become one of the topics that have interested researchers in recent years. In the first quarter of the 21st century, several studies were conducted that examined the role of different animals in the transmission of the parasite, possible natural hosts, and the elucidation of the zoonotic features of D. fragilis. In pioneering studies, various wild bird species and some domestic animals were examined, but the presence of D. fragilis was not detected (Ogunniyi et al. 2014; Stark et al. 2008b). However, as the scopes of the studies have been expanded, successful results are obtained. In a large-scale study conducted in Australia, 420 fecal samples were collected from 37 different animal species including cats, dogs, horses, lions, tigers and zebras, and all samples were examined for the presence of D. fragilis. In this comprehensive research, in terms of animal species, the method has also been strengthened by using three different diagnostic methods (conventional PCR, Real-time PCR and Nested PCR methods). As a result, D. fragilis DNA was detected in only 2 of 420 samples (a cat and a dog). There are no cattle among the 37 animal species included in the study (Chan et al. 2016).
In a study examining gastrointestinal parasites in the howler monkey species (Alouatta palliata aequatoriali), 96 stool samples were examined, and D. fragilis was detected in 3 samples (Helenbrook et al. 2015). In another study investigating the ectoparasites and endoparasites of rats in Nigeria, 50 house rats were examined for D. fragilis, and positivity was found in 2 of the animals (Ogunniyi et al. 2014).
A study similar to ours (due to the examination of livestock) reported the genotypes of D. fragilis detected. In a total of 152 pig feces samples, the presence of D. fragilis using microscopy and molecular methods was investigated. A total of 71 samples were positive for D. fragilis, and it was reported that pigs could be one of the natural hosts of D. fragilis. In addition, one of their sequences (Genbank Acc. No. JQ677148.1) showed 100% similarity with ours (Genbank Acc. No. ON242172), and it was also reported as genotype 1 (Cacciò et al. 2012). However, our study differs from others in terms of detecting the presence of D. fragilis in cattle for the first time and determining the genotypes of the isolates. In addition, the fact that the sequence we obtained is the same as genotype 1, which is the most frequently detected subtype in humans, supports the idea that the parasite may exhibit zoonotic transmission from cattle. It has also been thought that cattle may be one of the natural hosts for D. fragilis. In geographies where animal husbandry is common, diseases seen in these animals cause economic losses and threaten public health.