Comparative morphomolecular identification and pathological changes associated with Anisakis simplex larvae (Nematoda: Anisakidae) infecting native and imported chub mackerel (Scomber japonicus) in Egypt

Abstract

Native and imported Scomber Japonicus were collected from Egypt and found to be infected with the third stage larvae (L3) of Anisakidae. The Anisakidae larvae were found encapsulated tightly coiled in the mesenteries associated with pyloric ceca and the serosal surface of visceral organs and/or uncoiled larvae free in the abdominal cavity of infected S. japonicus. The prevalence, mean intensity, and mean abundance of L3 were 80%, 24.4, and 19.5 in imported fish, and they were 36%, 7.36, and 2.65 in native fish, respectively. These larvae were identified as Anisakis simplex type 1 based on their morphological and molecular characteristics. The larvae were cylindrical in shape, and the oral openings had a prominent boring tooth. The esophago-intestinal junction (ventriculus) was oblique. The bodies of the larvae were covered with a transversely striated cuticle. The posterior end of the larvae had a short mucron or spine. Subsequently, phylogenetic analysis of the internal transcribed spacer region and COI gene of investigated larvae confirmed the identification of A. simplex when compared with relevant species sequences in GenBank. Histopathological examination revealed multiple A. simplex larvae in the abdominal cavity near the pyloric appendages, stomach, and under the visceral peritoneum, which appeared as a very thin and glistening capsule covering the larvae with a prominent adhesive fibrinous peritonitis together with mononuclear and eosinophilic granular cell infiltration. The importance of A. simplex infection in both native and imported S japonicus in Egypt is emphasized.