Molecular Characterization of Eustrongylides sp. Infecting Channa punctata in Bangladesh

Eustrongylides (nematode: Dioctophymatidae) are parasitic nematodes of freshwater fishes and fish-eating birds. It has zoonotic potential and poses a threat to human health, as infection can occur through the consumption of raw or undercooked fish.

The present study was designed to characterize Eustrongylides sp. isolated from Channa punctata using the Internal Transcribed Spacer 2 (ITS2) regions.

In this study, a total of 137 medium-sized C. punctata (17.5 ± 2.5 cm) were collected from different locations of Jamalpur and Netrokona district, Bangladesh and isolated 44 nematodes. DNA was extracted from the parasites, amplified in the ITS2 region and sequenced.

All the nematodes were microscopically identified as belonging to the genus Eustrongylides based on morphological characteristics, including the presence of inner and outer circle labial papillae at the anterior end and the esophago-intestinal junction. Initially, the sequences were confirmed up to the lowest taxonomic level possible using Basic Local Alignment Search Tool (BLAST). For phylogenetic analysis, reference sequences of Eustrongylides sp. were aligned, and two single nucleotide polymorphisms (SNPs) were detected. The average sequence identity percentage (%) within the studied sequences ranged from 99.7% to 99.8%. A maximum-likelihood (ML) tree was constructed which showed that the studied sequences clustered within the Eustrongylides sp. lineage and grouped with reference sequences, supported by moderate bootstrap values (82%).

Close genetic similarity was observed when compared with reference sequences of Eustrongylides sp. Further studies on the investigation of genetic pattern of Eustrongylides sp. throughout the country are essential to control this parasite.