Blastocystis-positive IBS patients show higher IL-8 levels

In a cross-sectional study of symptomatic patients evaluated at a tertiary gastroenterology clinic, people with irritable bowel syndrome who carried Blastocystis had markedly higher serum interleukin-8 levels than IBS controls without the intestinal parasite. The finding links blastocystosis with a systemic pro-inflammatory signal in IBS, although the design cannot determine whether the infection contributes to symptoms, results from them, or reflects another underlying process.

Researchers assessed 298 symptomatic patients and diagnosed IBS using the Rome IV criteria, identifying 197 cases, or 66.1% of the cohort. Stool examinations found Blastocystis in 57 of those 197 patients, an infection prevalence of 28.9% within the IBS group. Parasite identification was performed by direct microscopy, while PCR with subtype-specific sequence-tagged site primers was used to classify the infections. These procedures detected two subtypes: subtype 3 accounted for 86% of Blastocystis-positive cases, and subtype 1 accounted for the remaining 14%.

To compare inflammatory responses, the investigators used a balanced random selection of 57 Blastocystis-positive IBS patients and an equal number of randomly chosen Blastocystis-negative IBS patients. Mean serum IL-8 concentration was 129.24 ± 56.28 pg/mL in the infected group, compared with 26.28 ± 9.28 pg/mL in the uninfected group. The difference was statistically significant at P < 0.001, indicating substantially elevated circulating IL-8 among the Blastocystis-positive participants. IL-8 is a chemokine involved in pro-inflammatory immune activity, making the association relevant to research on how intestinal infections may intersect with immune activation in functional gastrointestinal disorders.

The subtype analysis did not show that IL-8 concentrations differed significantly between subtype 3 and subtype 1, even though subtype 3 produced the numerically higher value. That distinction matters because subtype 3 was the predominant strain in this sample, but the study did not demonstrate a unique IL-8 response to that subtype. The authors therefore described the results as evidence of an association between Blastocystis infection and higher IL-8 in IBS rather than proof of a subtype-specific inflammatory effect.

Multivariable analysis identified younger age, diarrhea, and presentation during spring as independent predictors of Blastocystis infection. These variables were associated with the likelihood that an IBS patient carried the parasite; they do not establish that any of them caused infection or directly produced gastrointestinal symptoms. The sample was drawn from a single tertiary clinic and included symptomatic patients rather than a population-based control group. The cross-sectional comparison, modest number of infected participants, lack of longitudinal follow-up and absence of direct measurements of inflammation within the intestinal mucosa further constrain conclusions about causality.

The results add evidence to a continuing debate over whether Blastocystis has a meaningful role in IBS pathogenesis. The concentration of infections in a patient group with functional gastrointestinal symptoms and the accompanying difference in IL-8 are compatible with a potential aggravating influence, but the current data cannot establish that blastocystosis causes or worsens IBS. Distinguishing the effects of infection, subtype, host immunity, symptom pattern and other clinical characteristics will require mechanistic work and prospective studies.

The researchers also called for evaluation of local inflammatory markers to investigate immune modulation within the gut and identify molecular effectors that might connect Blastocystis with IBS. Such work would help determine whether the elevated serum IL-8 observed here reflects local intestinal activity, a broader systemic response, or another feature of the affected patients. Until those questions are resolved, the findings support a measured conclusion: Blastocystis was common among these IBS patients, subtype 3 predominated, and infection was associated with higher circulating IL-8, but the direction and mechanism of the relationship remain uncertain.

Subject of Research: Association between Blastocystis infection, subtype distribution and serum IL-8 in patients with irritable bowel syndrome

Article Title: Association of Blastocystis subtype 3 with elevated IL-8–mediated inflammation in patients with irritable bowel syndrome

Article References: Morsy, S. M., Abdeltawab, M. S. A., Mahfoz, A. M., Elkerdawy, M. A., Sallam, H. S., & Ismail, A. R. (2026). Association of Blastocystis subtype 3 with elevated IL-8–mediated inflammation in patients with irritable bowel syndrome. Gut Pathogens. https://doi.org/10.1186/s13099-026-00887-5

Image Credits: AI Generated

DOI: 10.1186/s13099-026-00887-5

Keywords: Blastocystis, irritable bowel syndrome, IL-8, intestinal parasites, inflammation, gut immunity, PCR, subtype 3, cross-sectional study, Association, subtype, elevated