Eimerian and capillariid infection in farmed ring-necked pheasants (Phasianus colchicus karpowi) in Ehime, Japan, with special reference to their phylogenetic relationships with congeners

We performed a parasitological examination of the gastrointestinal tract of farmed ring-necked pheasants (Phasianus colchicus karpowi) on two farms in Ehime, Japan. Fecal examination through flotation and sedimentation methods (43, 103, and 50 samples in three consecutive years from 2020, respectively) detected coccidian oocysts (5–58%), or capillarid (40–56%) and heterakid eggs (45–72%). Following artificial sporology, most sporulated coccidian oocysts were ellipsoidal without micropyle nor residuum, but with 1–3 polar refractile granules, morphologically reminiscent of Eimeria phasiani (Apicomplexa: Eucoccidiorida: Eimeriidae). Intensive sequencing of mitochondrial cytochrome c oxidase subunit I gene (cox-1) using pan-eimerian primers and multiple oocyst samples from different pheasants indicated a single species. We characterized, for the first time, the cox-1 sequence of E. phasiani, known to be prevalent in wild and captive ring-necked pheasants worldwide. Worm recovery under a dissection microscope revealed two capillariid and one heterakid nematode species: Eucoleus perforans (Nematoda: Trichocephalida: Capillariidae) in the esophageal epithelium (prevalence, 8–73%), Capillaria phasianina (Capillariidae) in the cecal mucosa (10–87%), and Heterakis gallinarum (Nematoda: Ascaridida: Heterakidae) in the cecal lumen (69–88%). The small subunit ribosomal RNA gene (SSU rDNA) of E. perforans was perfectly identical to that in a previous isolate from farmed Japanese green pheasants (Phasianus colchicus versicolor) at a distant locality in Japan. The SSU rDNA of C. phasianina was characterized, for the first time, demonstrating a sister relationship with Capillaria anatis, parasites found in the ceca of domestic ducks, geese, and various wild anatid birds.