Integrative morphological, SEM, and molecular characterisations of nematode larvae (Nematoda: Anisakidae) isolated from smoked herring fish in Ismailia Governorate, Egypt

Anisakiasis is a zoonotic disorder transmitted through fish that poses a substantial risk to human health through the ingestion of raw or uncooked seafood, making it a primary public health problem in developing countries. This investigation aims to determine the prevalence, site of infection, morphology, and genetic identification of Anisakid larvae (L3) in smoked herring ( Clupea harengus ) purchased from fish markets in Ismailia Governorate from February to April 2026. Prevalence was 93.5%, with a mean abundance of 3.88 larvae per examined fish and a mean intensity of 4.14 larvae per infected fish. Of the 775 larvae recovered, 611 (78.8%) lay free in the abdominal cavity, and 164 (21.2%) were embedded in tissue in 87 fish. Detailed morphological characters were clearly observed during light and Scanning Electron Microscopy (SEM) examinations, and identified the larvae as Anisakis sp. (Type I sensu Berland, 1961). Sequencing of the 18S rDNA gene from two specimens (702 and 686 bp) placed both isolates within the genus Anisakis ; both returned 100% identity and query coverage against reference sequences of A. simplex (MT246663.1) and A. pegreffii (MF072697.1), indicating that this region does not discriminate between members of the A. simplex complex. Maximum-likelihood analysis recovered Anisakis as monophyletic (81% bootstrap support) but yielded no supported resolution among species. The larvae are therefore reported as Anisakis sp. Sequences were deposited in GenBank under accession numbers PZ274382.1 and PZ274383.1. Because larval viability was not assessed, the findings are interpreted in terms of potential exposure to thermostable allergens rather than risk of active infection.