First molecular identification and genetic diversity of Giardia duodenalis and Blastocystis sp. in patients with...

Giardia duodenalis (G. duodenalis) and Blastocystis sp. are common intestinal protists with potential immunomodulatory effects. This study investigated their epidemiology, genetic diversity, and associated risk factors in patients with multiple sclerosis (MS) in western Iran, a population with immune dysregulation that may be vulnerable to opportunistic infections.

From June 2022 to November 2024, a cross-sectional study was conducted on 116 MS patients attenting neurology clinics in Sanandaj, Iran. Stool samples were analyzed using nested PCR targeting the triosephosphate isomerase(tpi) gene for G. duodenalis and direct PCR targeting the small subunit ribosomal RNA (ssu rRNA) gene for Blastocystis sp. All PCR-positive samples were sequenced. Phylogenetic analysis was performed using the Maximum Likelihood method. Multivariate logistic regression was used to identify risk factors.

The prevalence of G. duodenalis and Blastocystis sp. was 9.48% (11/116) and 12.06% (14/116), respectively. This prevalence is notable compared to some reports in the general Iranian population. Genotyping revealed G. duodenalis assemblages A (36.36%, 4/11) and B (63.64%, 7/11), and Blastocystis sp. subtype 1 (ST1) (28.6%, 4/14), ST2 (35.7%, 5/14), and ST3 (35.7%, 5/14). Multivariate analysis identified younger age (< 30 years; adjusted odds ratio [AOR] = 6.10, p = 0.007) and animal contact (AOR = 5.85, p = 0.030) as significant risk factors for G. duodenalis, while female sex (AOR = 8.31, p = 0.009) and animal contact (AOR = 4.79, p = 0.047) were significant for Blastocystis sp. Phylogenetic analysis confirmed the genetic diversity and suggested zoonotic potential of the identified isolates.

This first molecular study of G. duodenalis and Blastocystis sp. in Iranian MS patients highlights a notable prevalence of these parasites. The significant association with animal contact and the identification of assemblages/subtypes with low host specificity underscore a potential zoonotic risk. These findings suggest that such infections may be underrecognized in MS populations and warrant consideration in clinical management, including potential screening and public health interventions to mitigate risk.