Veterinary Physiology

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Molecular survey on Sarcocystis Species in Slaughtered Sheep in Hamedan, Iran

Samaneh Shakeri1 and Ghazaaleh Adhami2*

1 DVM, Faculty of Veterinary Medicine, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran

2 Assistant Professor, Department of Veterinary Pathobiology, Faculty of Veterinary Medicine, Islamic Azad University, Sanandaj Branch, Sanandaj, Iran * Corresponding author: Ghazaaleh Adhami, Department of Veterinary, Pathobiology, Faculty of Veterinary Medicine, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran. Email:


Introduction: Sarcocystis is an apicomplexan heteroxenous protozoan leading to adverse consequences for production in sheep with remarkable importance in public health. The current study aimed to investigate molecular prevalence data on Sarcocystis spp. in slaughtered sheep using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in Hamedan, Iran. Methods and materials: The carcass of 60 sheep slaughtered in the Hamedan abattoir was sampled from May 2019 to June 2020. Heart, scapular, esophageal and diaphragmatic muscles were macroscopically examined and recorded as positive in case of the presence of tissue cyst. In this regard, 50 grams of each muscle was sliced and transferred to the laboratory on ice for microscopic and molecular analysis. The molecular identification of Sarcocystis spp. was performed using the PCR-RFLP method. Results: By microscopy, all specimens contained bradyzoites in cysts. The molecular analysis further revealed Sarcocystis species, including Sarcocystis gigantea (S. gigantea), S. tenella, and S. arieticanis. Conclusion: The present study emphasized that three Sarcocystis spp. were circulating among sheep and carnivorous hosts in the investigated area. Further molecular investigations are highly recommended to better evaluate the epidemiology of this zoonotic parasite.

  1. Introduction: Sarcocystosis is a global parasitic disease of the musculoskeletal system in various animals, such as mammals, birds, reptiles as well as humansˡ. Sarcocystis spp. is an obligatory intracellular heteroxenous parasite, circulating among definitive carnivorous hosts (canids and felids) as predators and herbivorous intermediate hosts, such as cattle, sheep, goat, buffalo, and camel as preyˡ. Sexual reproduction occurs in definitive hosts, shedding sporocysts into the environment versus feces. In contrast, asexual reproduction and schizogony occur in striated and heart muscles of intermediate hosts, leading to Sarcocystis formationˡ. Hence, ingesting food/water contaminated with sporocysts and devouring carcasses infected with sarcocyst are the main routes of transmission in intermediate and definitive hosts, respectively2. In this sense, consumption of highly infected meat from food animals is not suitable for humans2. The most widespread Sarcocystis species include Sarcocystis tenella (S. tenella), S. arieticanis, S. medusiformis, and S. gigantea (ovifelis) in sheep as well as S. hominis (bovihominis), S. cruzi (bovicanis) and S. hirsute (bovifelis) in cattle. Sarcocystis infections in the definitive hosts are frequently asymptomatic, while they may inflict mild disease by S. gigantea in sheep, to acute disease by S. cruzi in cattle and S. capracanis in goat3. Cellular degeneration, hemorrhage, and inflammatory lesions are the most observed pathologies induced by the parasite4. Invasion of the nervous system is rare, except for S. neurona, which develops the nervous disease in some animal species4. In pregnant sheep, the acute disease may result in abortion, fetal death, and still birth5. The most prominent pathologic traits of the infection develop following merozoite release in the circulation6. Generally, the parasite undergoes two merogony cycles. The first-generation meronts are formed 1-2 weeks upon infection in endothelial cells of blood vessels in most body organs, and the second-generation meronts emerge 3-5 weeks post-infection, leading to systemic intravascular coagulation, perivascular inflammation, necrosis, and hemorrhage7. Fever directly correlates to the rate of parasitemia, resulting in anemia due to the constant bleeding related to extravascular hemolysis on an immunologic basis. Animal death occurs after ingestion of a huge number of sporocysts, which usually coincides with second-stage merogony7. Sarcocystis species involving canid hosts may result in fetal death and abortion in infected, non-immune animals. Nevertheless, no exact underlying mechanism is determined for Sarcocystis-induced abortion, and the parasite has been rarely isolated from the infected fetus and placenta under experimental conditions8. Diagnosis of the infection in livestock depends on several approaches, including abattoir-based macroscopic examination of infected organs in animal carcasses, microscopic observation of tissue cysts using digestion and/or stamp method as well as trichinoscopy, along with immunohistochemical and molecular techniques9. Bradyzoites of various Sarcocystis spp. released by the digestion method could not be differentiated due to the morphological similarities in the bradyzoite’s shape9. Several serological-based methods are available for detecting sarcocystosis in sheep such as enzyme-linked immunosorbent assay (ELISA) and an indirect fluorescent antibody test (IFAT), with significant sensitivity in the late phase of infection10. However, discrimination between sheep pathogenic and non-pathogenic Sarcocystis spp. is impossible using such methods10. With the advent of molecular techniques, species identification of parasitic agents has been facilitated, which provides a deeper understanding of Sarcocystis epidemiology11. In Iran, the prevalence rates of Sarcocystis infection among sheep and cattle populations were reported at 80% and 100%, respectively. With this in mind, the present cross-sectional study aimed to investigate Sarcocystis prevalence rate and involved species in sheep of Hamedan, western Iran, using the polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP) method.

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