Morphological and molecular appraisal of cyclophyllidean cestoda parasite Raillietina saudiae sp. nov. infecting the domestic pigeon Columba livia domestica and its role as a bio-indicator for environmental quality

摘要

Pigeons members of the order Columbiformes are a cosmopolitan group of birds with abundant and large populations associated with human activities. Therefore, the current study was conducted to determine the parasitic infections within the domestic pigeon Columba livia domestica. Eighteen pigeons were examined for the presence of gastrointestinal helminths, of which 77.78% were infected with a cyclophyllidean cestoda parasites. The morphology of this parasite based on light and scanning electron microscopic studies, revealed the presence of gravid worms, 2.00-4.52 cm long and 0.23-0.59 mm wide; a scolex had four suckers equipped by 5-6 rows of minute hooks and retractable rostellum with 230-250 hooks; genital pores unilateral; oval testes with 27-37 in number; bibbed ovary; post-ovarian vitelline gland; and 24-28 egg capsules present in uterus with 5-6 spherical eggs in each capsule. Molecular analysis based on sequences of ITS2 and ND1 gene regions was performed to confirm the taxonomy of this parasite based on its morphology. This revealed close identity of up to 92.0% and 72.0% for ITS2 and ND1 gene regions, respectively, with other cestoda species obtained from GenBank. Phylogenetic analysis supported the placement of this cycllophylid species within Davaineidae with close relationships to the previously described species of R. chiltoni, R. dromaius, and R. beveridgei based on the ITS2 gene region and R. coreensis and R. sonini based on the ND1 gene regions. Heavy metals accumulation in the recovered parasite and its host showed significantly higher concentrations in the parasite compared to its host tissues. Generally, concentrations of metals exceeded the permissible limits recommended by the US Environmental Protection Agency. Therefore, pigeon cestodes can be regarded as useful bio-indicators when evaluating the environmental pollution of terrestrial ecosystems by heavy metals.