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Two models for pathology of third stage Anisakis larvae - Sprague-Dawley rat (Rattus norvegicus) and European sea bass (Dicentrarchus labrax)

Consumption of raw or thermally lightly processed sea food contaminated by live third stage larvae of Anisakis spp. can lead to a zoonotic disease anisakiasis. In severe cases perforation of gastric or intestinal wall occurs caused by larval migration. Histopathologic changes in such cases include severe eosinophilia and subsequent formation of eosinophilic granulomas. The aim of the study was to compare two host models experimentally infected by Anisakis larvae ; Sprague-Dawley rat (Rattus norvgicus) as a model for human infection, and European sea bass, as a model paratenic host. Rats (n=15) and European sea bass (n=24) were each experimentally infected with 10 live third stage larvae of Anisakis spp. by oro-gastric intubation. Animals were euthanized, dissected and inspected for migrating larvae. Tissues with embedded larva migrans and consequent lesions caused by its migration were sampled and processed for classical histopathological analysis and transmission electron microscopy (TEM). In rats, Anisakis larvae were mostly found penetrating gastric wall and rarely intestinal wall, abdominal musculature or subcutaneous fat tissue. Histopathological analysis showed deep ulcerations of glandular epithelium in gastro-intestinal wall together with tissue necrosis at the site of larval penetration. Severe haemorrhages were present in lamina propria mucosae together with extensive neutrophil and eosinophil infiltration. In affected muscles structural disintegration and necrosis of muscle fibres was observed, accompanied by infiltration of neutrophils and eosinophils, some of which showed degranulation as revealed by TEM. In European sea bass, Anisakis larvae were found penetrating gastric or intestinal wall only in small number of infected animals indicating successful expulsion of nematodes by host's peristaltic. Lesions caused by larval migration were mostly characterized by ulcerations and necrosis of glandular epithelium and moderate infiltration of mast cells in lamina propria mucosae. Due to acute infection only, wound healing occurred rapidly and without proliferation of connective tissue. These findings demonstrate that rats, congruent to humans and both being accidental and naïve hosts, mobilize strong innate immunity resources against an unknown pathogen, such as Anisakis. In contrast, fish as an evolutionary long-lasting paratenic host exhibits considerably milder immune response with rapid wound healing processes.

Anisakis ; Rattus norvegicus ; Dicentrarchus labrax ; pathology

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