Mitochondrial genome, nuclear ribosomal RNA gene, and morphological-tegumental analysis of dermatitis-causing cercariae: Trichobilharzia sp. from Thailand.

Avian blood flukes of the genus Trichobilharzia, the largest subgroup of the Schistosomatidae family, are of medical and veterinary importance as causative agents of avian schistosomiasis and human cercarial dermatitis. Despite their significance, molecular data on Trichobilharzia species from Southeast Asia remain limited, and no mitochondrial genomes have been reported to date. This study presents the first complete mitochondrial genome and nuclear ribosomal RNA (rRNA) gene analysis of a Trichobilharzia sp. isolate (PYO) recovered from Radix (Lymnaea) rubiginosa in Phayao, Thailand, alongside comprehensive morphological characterization. Genomic features were analyzed using sequence-based and systematic approaches, while cercarial morphology and tegumental structures were examined in detail through light, confocal, and scanning electron microscopy (SEM). The morphological characteristics were generally consistent with those of other Trichobilharzia species. The circular mitochondrial genome of the PYO isolate is 14,810 bp in length, comprising 12 protein-coding genes (PCGs), 2 rRNA genes, 22 transfer RNA genes, and a repeat region. Gene content and arrangement were consistent with previously reported Trichobilharzia mitogenomes, with all genes transcribed in the same direction. ATG and TAG were the most common start and stop codons, respectively. Comparative analysis of nuclear and mitochondrial sequences consistently identified T. regenti, the most virulent and well-characterized species in the genus, as the closest relative of the PYO isolate, highlighting its potential medical and epidemiological significance.