Association of Blastocystis species subtypes 3 and 4 with intestinal inflammation and response to metronidazole in symptomatic patients

Blastocystis spp. (BC) often passes as a harmless resident of the gut. However, it may be associated with gastrointestinal disturbances, such as abdominal pain and diarrhea. The variation in the clinical spectrum of BC infection is, in part, due to its diverse genotypic profile, where ongoing research continues to discover new BC subtypes. This study aimed at investigating the association between different BC subtypes and intestinal inflammation as assessed by fecal calprotectin (FCP) and tumor necrosis factor alpha (TNF-α) levels. Patients complaining of gastrointestinal tract (GIT) symptoms were investigated for the presence of BC infection by microscopy and stool culture on Jones’ medium. Out of 163 patients, 88 were confirmed to be infected with BC. They were further divided according to the dominant BC subtype by RFLP genotyping. Patients were treated with metronidazole at a dose of 250 mg 3 times daily for ten days and were evaluated for symptom improvement after the treatment course. Moreover, FCP and TNF-α levels were measured in stool samples by ELISA before and after therapy. BC subtype 3 was found to be the dominant subtype in 62 samples (70.5%), while subtype 4 was dominant in 26 samples (29.5%). A higher number of patients infected with BC subtype 3 reported the presence of GIT manifestations. After treatment, 17 subtype 3-infected patients (27.4%) witnessed improvement of their GIT symptoms, as compared to 9 patients infected with BC subtype 4 (34.6%). In subtype 3 infected patients, 71% were free of BC stages by both microscopic examination and stool culture, while 92.3% of patients infected with subtype 4 showed fecal parasite clearance. FCP and TNF-α levels were higher in patients infected with BC subtype 3 as compared to BC subtype 4, both before and after treatment with metronidazole. In the BC subtype 3-infected groups, fecal TNF-α and FCP levels decreased significantly after treatment. In our cohort study, BC subtype 3 was the most prevalent subtype among patients reporting gastrointestinal symptoms. The ST3 group exhibited numerically higher inflammatory markers compared to ST4. These trends shed light on the potential link between Blastocystis genetic diversity and intestinal inflammation. Although the observational nature of this study and the unequal group sizes limit the ability to establish a definitive causal relationship, these findings provide a BC subtype-oriented diagnostic and therapeutic design within a hospital-based setting that could facilitate the design of more tailored management strategies for patients with BC-associated symptoms.