Molecular identification and genetic diversity of equine ocular setariasis in Thailand based on the COI, 12S rDNA, and ITS1 regions.

Equine ocular setariasis is mainly caused by Setaria digitata, and the identification of this filarial nematode is based on morphology. However, morphological characterization alone is insufficient for the detection and differentiation of S. digitata from its congeners. In Thailand, the molecular detection of S. digitata is lacking and its genetic diversity is still unknown. This study aimed to phylogenetically characterize equine S. digitata from Thailand based on sequences derived from the mitochondrial cytochrome c oxidase subunit 1 (COI), the mitochondrial small subunit ribosomal DNA (12S rDNA), the nuclear internal transcribed spacer 1 (ITS1) and Wolbachia surface protein (wsp). Five samples of S. digitata were characterized, submitted to the NCBI database, and used for phylogenetic analysis as well as the assessment of similarity, entropy, and haplotype diversity. Phylogenetic analyses revealed that the S. digitata Thai strain was similar to S. digitata from China and Sri Lanka, with 99 to 100% similarity. The entropy and haplotype diversity indicated that the S. digitata Thai isolate was conserved and closely related to S. digitata worldwide. This is the first report on the molecular detection of equine ocular setariasis caused by S. digitata in Thailand.