Taxonomy of the cestodes Avitellina sudanea and A. centripunctata (Cyclophyllidea, Thysanosomatidae) parasitic in sheep and goats in India based on morphological and molecular evidence.

This study presents morphological, molecular and phylogenetic analyses of two species of the genus Avitellina, A. sudanea and A. centripunctata parasitic in sheep and goats and sampled in the region of the City of Chandigarh, North India. Three molecular markers were used: mitochondrial cytochrome c oxidase subunit 1 (cox1), nuclear small subunit ribosomal RNA (SSU rDNA) and internal transcribed spacer 1-5.8S rRNA (ITS1-5.8S rDNA) genes. Morphological analysis revealed differences in key structures, including paruterine organ shape and testis arrangement. Molecular analysis revealed that A. sudanea showed no exact match but significant similarity with other species: A. lahorea and A. centripunctata, exhibiting 91.39% and 85.89-86.52% (SSU rDNA), 96.27 and 94.31% (cox1), 94.19 and 94.41% (ITS1-5.8S rDNA) sequence similarity, respectively. The Maximum Likelihood phylogenetic trees based on DNA sequences of SSU rRNA, cox1 and ITS1 placed these species in a separate clade, which was distinct from anoplocephalids (sensu stricto) and supported the thysanosomatids as a distinct taxon at the family level. The evolutionary divergence based on base substitution rates confirmed substantial interspecific genetic distinctions, with high divergence values of 0.12 (cox1), 0.25 (SSU rDNA) and 0.11 (ITS1-5.8S rDNA) between A. sudanea and A. centripunctata. This study provides the first molecular characterization of A. sudanea, confirming its genetic distinctiveness and taxonomic status as a valid species. Our findings highlight the necessity for more molecular studies on Avitellina tapeworms using robust genetic tools to ensure accurate taxonomic delineation within the genus.