Persistent asymptomatic eosinophilia after raw seafood exposure with normal IgE: a case report

Marine seafood-derived anisakid nematodes (e.g., Anisakis spp. and Phocanema spp. [formerly Pseudoterranova spp.]) may cause gastrointestinal and allergic manifestations. Here, we report an unusual case of persistent, asymptomatic peripheral eosinophilia following ingestion of raw or lightly marinated seafood, raising the possibility of subclinical antigenic stimulation. The patient remained entirely asymptomatic with normal total IgE levels, and parasite serology (including Angiostrongylus cantonensis IgG) was negative, yet developed marked eosinophilia. The patient had a childhood history of allergic diseases that fully resolved in adulthood, which may represent an immunologic background relevant to the unusual presentation of marked eosinophilia with persistently normal total IgE. Although the underlying mechanism could not be directly demonstrated, this pattern raises the possibility of a predominantly eosinophil-associated type 2 response without a prominent humoral allergic manifestation. The eosinophil count remained persistently elevated over several months and stayed markedly above the adult upper reference limit before treatment, while comprehensive evaluations for parasitic infection, infectious disease, and autoimmune conditions were negative. Bone marrow findings demonstrated reactive eosinophilic hyperplasia, and imaging studies were unremarkable. Following empiric albendazole therapy, the eosinophil count rapidly returned to normal. This temporal association was supportive of, but not diagnostic for, a parasite-related or antigen-mediated trigger in this otherwise unexplained case. This observation aligns with the latest UK Guideline for the Investigation and Management of Eosinophilia, which recommends considering empiric anthelmintic therapy in asymptomatic patients without an identifiable cause. This case suggests that in patients with otherwise unexplained asymptomatic eosinophilia, even a remote and limited history of consuming raw or lightly marinated seafood should not be overlooked during history taking, and that empiric anthelmintic therapy may offer practical diagnostic and therapeutic value in selected cases.