Genetic assemblages of Giardia duodenalis linked to distinct symptom profiles

Giardia duodenalis is a common intestinal parasite that infects children and adults worldwide. Of its eight known assemblages (A-H), assemblages A and B are the predominant genotypes infecting humans. The infection ranges from asymptomatic to chronic diarrhea, but whether disease severity depends on parasite strain or host factors remains unclear. This study analyzed Giardia isolates from non-Inflammatory Bowel Disease (non-IBD) and Inflammatory Bowel Disease (IBD) patients at PGIMER, Chandigarh, to explore link between assemblage type and symptom severity. A total of 180 non-IBD and 80 IBD patients were enrolled categorized into mild, moderate, and severe groups based on symptom severity scores. Detection was done by microscopy and nested PCR, followed by assemblage specific conventional and real-time PCR. The present study revealed that among non-IBD patients, 20 cases were identified as assemblage A, 25 as assemblage B, and 2 as mixed assemblages. Among IBD patients, 4 cases each were classified as assemblage A and assemblage B. Assemblage B predominated in the severe symptom group among non-IBD patients. In IBD patients, a possible association of assemblage A with severe symptoms was observed, although this finding remains preliminary due to the limited sample size. In non-IBD cases, assemblage A was frequent in females and B in males, while in IBD cases, assemblage A dominated in males and B showed equal distribution. This study reveals novel association between Giardia assemblages and symptom severity, highlighting the value of assemblage-level detection for better diagnosis and treatment, and the role of host factors in disease outcome.