Nematodes of the family Anisakidae are parasites that pose significant concerns to human and aquatic animal health. They possess a complex life cycle involving crustaceans as first intermediate hosts, fish or cephalopods as second intermediate or paratenic hosts, and marine mammals as definitive hosts. Reports of Anisakis typica infections are common in several teleost fishes across the region, including India, Indonesia, and Malaysia, yet their genetic variation remains inadequately characterized. In this study, Anisakis typica larvae isolated from three commercially important fishes Auxis thazard, Psettodes erumei and Decapterus sp. from India, Indonesia and Malaysia respectively.
Identification was carried out using both morphological and molecular methods. The phylogenetic relationship of A. typica was analysed using the Internal Transcribed Spacer (ITS: ITS1–5.8S–ITS2) region of the ribosomal RNA gene. Maximum likelihood phylogenetic trees were constructed using the Tamura–Nei model in MEGA v12 with 1000 bootstrap replicates, while genetic diversity was assessed using DnaSP v6. The resulting phylogeny clustered all eleven A. typica isolates from different geographic locations together, clearly separating them from other anisakid species. Genetic diversity parameters from the ITS region indicated low haplotype (Hd = 0.3455) and nucleotide diversity (Pi = 0.00129), with neutrality tests (Tajima’s D = –1.85059, Fu and Li’s D and F < 0, P < 0.05) suggesting an excess of rare polymorphisms, possibly reflecting recent population expansion.
This study enhances understanding of the genetic structure and phylogenetic position of A. typica in the region. The low genetic diversity across countries suggests limited population differentiation, potentially due to wide host distribution and larval dispersal through migratory fish hosts. These findings provide a genetic baseline for future epidemiological studies and for improving fishery and public health management strategies related to anisakid infections.