Prevalence of Anti-Anisakis simplex Antibodies in a Cohort of Patients with Inflammatory Bowel Disease in Norway

This study assessed the seroprevalence of anti-<i>Anisakis simplex</i> antibodies in Norwegian patients with inflammatory bowel disease (IBD), specifically ulcerative colitis (UC) and Crohn's disease (CD), compared with healthy controls. Associations between anti-<i>A. simplex</i> antibody positivity and clinical or laboratory parameters in IBD were also explored. A total of 86 UC patients, 68 CD patients, and 41 healthy controls were prospectively enrolled from four Norwegian hospitals (2013-2022). Diagnosis and disease activity were established using standard clinical, endoscopic, and biomarker criteria. Serum samples were analyzed for total Ig, IgG, IgM, IgA, and IgE antibodies against <i>A. simplex</i> and <i>Pseudoterranova decipiens</i> using ELISA. Anti-<i>A. simplex</i> IgG seroprevalence was 4.9% in controls and 3.2% in IBD (3.5% UC, 2.9% CD). IgM seroprevalence was 0% in all groups. IgA seroprevalence was higher in IBD (16.2%) than controls (4.9%), with 14.0% in UC and 19.1% in CD. IgE seroprevalence was low across all groups. Smoking correlated with lower antibody levels and higher surgery rates. In UC, higher anti-<i>A. simplex</i> IgG and IgE levels were associated with milder disease and better prognosis. Anti-TNFα and azathioprine treatments were linked to higher anti-<i>A. simplex</i> IgA. Norwegian UC and CD patients had significantly higher anti-<i>A. simplex</i> total Ig and IgA seroprevalence than healthy controls, indicating increased exposure or immune response. Anti-<i>A. simplex</i> IgG and IgE may serve as markers of clinical activity in UC. Further research is warranted to clarify the clinical significance of these findings.