Third-stage nematode larvae of Contracaecum osculatum from Baltic cod (Gadus morhua) elicit eosinophilic granulomatous reactions when penetrating the stomach mucosa of pigs.

Third-stage larvae of the anisakid nematode Contracaecum osculatum were recovered from livers of Atlantic cod (Gadus morhua) caught in the Baltic Sea (June 2014) and used for experimental infection of two pigs (one male and one female). Each pig received 215 larvae by oral infection (feeding with minced cod liver containing live nematode larvae). Pigs were euthanized after 5 days, necropsied, and subjected to parasitological investigation. A total of 12 larvae were found penetrating the mucosa of the ventricle (7 in the female pig and 5 in the male pig) eliciting a granulomatous reaction at the penetration site. Four non-attached larvae were found in the female pig stomach and one in the male pig. Petechial bleeding was observed at several locations in the ventricular mucosa where larvae were located. Histological examination of the stomach mucosa revealed a massive cellular infiltration (giant cells, lymphocytes, macrophages, granulocytes, and fibroblast like cells) around the penetrating larva. Mononuclear and polymorphonuclear cells containing eosinophilic granulae were particularly prominent in the granulomas. Reactions correspond to reactions in pigs following experimental infection with the human pathogenic anisakid larvae Anisakis sp. and Pseudoterranova sp. which suggests that C. osculatum might have a zoonotic potential as well.