Morphological and molecular characterization of Anisakis simplex (Nematoda: Anisakidae) third-stage larvae isolated from retail-marketed smoked herring fish in Assiut, Egypt

Background: Clupea harengus, Linnaeus, 1758 is a nutritious pelagic fatty herring, rich in omega-3 fatty acids. Its consumption is associated with human anisakiasis as an intermediate host of Anisakis spp. Objective: To identify the anisakid larval detection rate in smoked C. harengus in Assiut Governorate, Egypt and characterize the morphological and molecular features of Anisakis spp. 3rd stage larvae. Material and Methods: The collected anisakid larvae from marketed herring were examined by light and scanning electron microscope (SEM). Characterization of anisakid larvae was performed by PCR as well as sequencing analysis of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA). Results: The detection rate of Anisakis spp. 3rd stage larvae among the smoked herring was 72% with larval load varying from 2-63 larvae per fish. Macroscopically, they appeared as coiled spiral buttons, yoyo-like, tangled, and free shapes. Larvae were found on the surface of fish gonads, livers, intestinal tracts, mesenteries, and abdominal cavities. The larval body was covered with a cuticular layer and had a marked boring tooth, and mucron. The molecular and phylogenetic analysis, using ITS gene, identified the collected larvae as A. simplex and was registered in the GenBank under the accession number OR660093.1. Conclusion: Detection of Anisakis 3rd stage larvae was marked in smoked herring sold in Assiut Governorate, Egypt. Further studies are recommended to investigate the endemicity of Anisakis larvae in imported fish.