This paper aimed to investigate the diversity and burden of helminthiasis in Ovis orientalis (n = 26), Capra aegagrus (n = 29) and Gazella subgutturosa (n = 24) grazed in 37 National Parks in 9 provinces of Iran. The organs and body cavities infected by helminths included gastrointestinal tract, peritoneal cavity, heart, liver and lungs. The contents were extracted and washed under running water and intestinal and lung-isolated nematodes were cleared in lactophenol and subsequently fixed, and cestodes were stained with alum carmine and mounted en face in Berlese's fluid under slight pressure between a microscopic slide and cover slip. The helminth species identified in this study include: intestinal nematodes (Marshallagia marshalli, Teladorsagia circumcincta, Ostertagia ostertagi, Nematodirus oiratianus, Nematodirella longispiculata, Skrjabinema ovis, Trichuris ovis, Trichuris discolor, Parabronema skrjabini), lungworms (Protostrongylus rufescens, Cystocaulus ocreatus), adult cestodes (Moniezia expansa, Helicometra giardi, Avitellina centripunctata, Stilesia globipunctata) and metacestodes (Cysticercus spp., hydatid cyst, Cysticercus tenuicollis). The proportion of the different helminth species ranged from low to moderate (3.45-46.15%) and the intensity of helminth isolation from the different ruminants ranged between 2 and 20. All the taxa identified in our study have been reported in wild animal species around the world. The presence of Cysticercus spp. with cardiac involvement in G. subgutturosa and all helminths of C. aegagrus was reported for the first time in Iran. A significant reduction was observed in worm burden, compared with previous studies in Iran, indicating changes in wildlife host-parasite systems, which can be linked to many reasons including climate changes, public health policies (e.g., strategic anthelmintic use in domestic ruminants), anthropogenic factors and environmental changes (e.g., urbanization or agricultural expansion, physical barriers), as well as vegetation growth and host availability.
