Sensitization to Anisakis simplex (A. simplex) has been documented to produce severe allergic reactions following ingestion of mainly raw or under-cooked parasitized fish. False positive skin prick tests (SPT) or specific IgE against this nematode and cross-reactivity restricts diagnosis. Gastric anisakiasis and gastro-allergic anisakiasis occur if fish is parasitized by live A. simplex
To investigate if serial serological analysis could be useful in the diagnosis of acute parasitation by this nematode.
We included 41 patients who experienced an allergic reaction and/or abdominal symptoms after ingestion of raw or undercooked fish and displayed specific IgE against A. simplex. Total and specific IgE were determined two times: in the 24-h period after onset of clinical symptoms and after 1 month. SPTs were performed against A. simplex and implicated fish. A fibre optic gastroscopy was performed in 22 patients.
Median total IgE was 80.0 (Interquartile range [IQR] 41.5–186.5) kU/L in the first evaluation and 247.0 (IQR 96.5–649.5) kU/L after 1 month. Median specific IgE against A. simplex was 11.4 (IQR 7.1–33.5) kU/L in the first 24 h and 36.8 (IQR 19.5–79.5) kU/L after 1 month. A rise of total IgE was observed in 35 of 41 patients (P < 0.00001) and a rise in specific IgE against A. simplex in 37 of 41 patients (P < 0.00001). Mean percentage increment was 392% (215–571%; 95% confidence interval [CI]) for total IgE and 339% (177–502%; 95% CI) for specific IgE. In nine of 22 gastroscopic examinations at least one larva, identified as A. simplex, could be detected by our microbiology service. In this group (n = 9) a rise of total and specific IgE was detected in eight patients (89%) (P = 0.02).
We consider a rise of total and specific IgE in the first month after an allergic reaction as a useful tool in the diagnosis of gastro-allergic anisakiasis (together with patient's history), even if the parasite cannot be seen with fibre optic gastroscopy. The important rise of total and specific IgE against A. simplex can be considered as a reaction induced by the live parasitizing larva in the context of a polyclonal immunological stimulation.