Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 14 1 2019 03 11 174 179 EN J. Raúl LUCAS Veterinary Institute of Tropical and High Altitude Research, School of Veterinary Medicine, National University of San Marcos, Junin, Peru Manuel BARRIOS-ARPI Physiology Laboratory, School of Veterinary Medicine, National University of San Marcos, Lima, Peru José RODRÍGUEZ Veterinary Institute of Tropical and High Altitude Research, School of Veterinary Medicine, National University of San Marcos, Junin, Peru Stephanie BALCÁZAR-NAKAMATSU Veterinary Institute of Tropical and High Altitude Research, School of Veterinary Medicine, National University of San Marcos, Junin, Peru Jacquelyne ZARRIA Specialized Equipment Laboratory, Faculty of Biological Sciences, National University of San Marcos, Lima, Peru Gislene NAMIYAMA Electronic Microscopy Nucleus, Adolfo Lutz Institute, Sao Paulo, Brazil Noelia TANIWAKI Electronic Microscopy Nucleus, Adolfo Lutz Institute, Sao Paulo, Brazil Omar GONZALES-VIERA Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA 2017 01 27 2019 03 11 Background: Recently, it was proposed the name of Sarcocystis masoni n. sp. for the Sarcocystis that causes microcyst in skeletal muscle of South American camelids. However, there are no ultrastructural reports of microcysts of Sarcocystis in cardiac muscle of alpacas. This study reports ultrastructural features of microcysts of Sarcocystis sp. from cardiac muscle of naturally infected alpacas. Methods: Thirty alpacas (age range: three to five years) from the province of Junin, Peruvian Central Andes, were included in this study in January 2015. Cardiac muscle samples were evaluated by histology and transmission electron microscopy. Results: Bradyzoites in cysts had typical characteristics of Apicomplexa including organelles, a large nucleus, micronemes, dense bodies, and polysaccharide granules. Moreover, cysts had a thin wall with numerous, short, finger-like shapes with rounded tip protrusions (0.51 x 0.17 µm). Conclusion: Sarcocystis sp. from the heart and S. masoni n. sp. from the skeletal muscle have similar ultrastructural characteristics. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/1444 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/1444/927