Blastocystis is an enteric parasite found in animals and humans with a worldwide distribution [20, 21]. Many studies have emphasized the importance of its pathogenic role [22-24]. In Syria, Blastocystis is considered part of the intestinal flora; it is not yet recognized as a pathogen and it is not specified usually, in the results of any laboratory analysis of the fecal sample. Hence, we aimed to focus on the different diagnostic methods and its sensitivity and specificity in the accurate diagnosis of Blastocystis.
Our findings showed notable difference in the detection of Blastocystis in stool isolates using the three diagnostic methods. The presence of this parasite was recorded in 70% of samples by microscopy, in 85.7% by in vitro culture and in 91.4% by conventional PCR.
Laboratory diagnosis of Blastocystis can be challenging and the prevalence data can be influenced depending on the method of diagnosis, making choosing the accurate method an important task in diagnosing Blastocystis .
Blastocystis is highly polymorphic it has variation in size and shape [26, 27]. Our microscopic data showed that the vacuolar and granular forms were mostly detected using microscopic examination. This finding is in agreement with previous results since these forms are easily distinguished from other protozoa [28, 29]. On the contrary, other studies indicated the presence of vacuolar, granular, amoeboid and cyst forms of Blastocystis in the microscopic detection [30, 31]. Thus, relying on using microscopic examination only in diagnosis is controversial and many studies underestimated it [27, 32]. Additionally, the low microscopic sensitivity recorded in our study may be according to some researches due to the Lugol’s staining method which shows less sensitive than cultivation in Jones’ medium [17, 33].
On the other hand, our data showed that in vitro culture failed to detect the parasite in 6 positively proved cases by PCR. This results may be explained either because they were disintegrated prior to culturing or for some conditions that affected its growth and hence detection in culture [11, 34].
Despite its high cost, PCR is considered as a gold standard detection assay with no time consuming, in comparison with in vitro culture method that is time consuming, yet microscopy detection needs experience but with low cost. Our diagnosis results are consistent with previous studies that indicated that molecular assays and in vitro culture are superior over the direct microscopic examination in the detection of Blastocystis from human stool isolates [17, 35, 36]. However, some studies suggested that in vitro culture is superior to direct PCR assay [32, 37].
False-negative results using PCR were detected in two positively confirmed isolates by microscopy and culturing techniques. Even though, there is no clear explanation for such results, low concentration of DNA, the presence of PCR inhibitors in some specimens or degradation of parasite material during storage may be the cause [11, 38].
Remarkably, the majority of our samples (65.3%) showed the presence of Blastocystis alone, while co-infection with other intestinal parasites was detected in 34.7%. This finding strongly indicates the importance of considering Balastocystis in laboratory diagnosis. It also agrees with that our patients showed enormously different symptoms, making it hard to associate Blastocystis presence with specific gastrointestinal symptoms and emphasize the importance of recognizing it as a pathogen agent.