Sarcocystosis is a zoonotic disease in sheep caused by an intracellular parasite belongs to the phylum Apicomplexa, order Eucoccidioria, and Sarcocystidae family. In the parasite life cycle, there is a need for an intermediate host and a definite host. Some species of Sarcocystis can cause disease and consequently cause weight loss, anorexia, fever, anemia, muscle weakness, decreased milk production, abortion, and sometimes death in intermediate hosts such as cattle, goats, and sheep. Cysts of Sarcocystis spp. are found nearly always in skeletal, striated muscles, particularly in the diaphragm, heart, liver, lungs, and esophageal. A six-years-old native ewe was referred to the veterinary clinic in Najafabad, Isfahan province, Iran with major clinical signs of nasal discharge, enlarged superficial lymph nodes, anorexia, and a round tumor-like mass on the back. After tissue processing and hematoxylin and eosin staining, different sizes of Sarcocystis spp. (with 3.03 ± 0.44 µm in length) each surrounded by a thin layer of muscle fibers and contained banana-shape bradyzoites were seen in the subcutaneous muscle fibers. Hemorrhage and infiltration of inflammatory cells, mainly, neutrophils were also seen in the dermis.
Keywords: Sarcocystosis, Ewe, Histopathology, Case report
Sarcocystosis, a food borne zoonotic disease, is caused by Sarcocystis spp. with worldwide distribution in humans, animals, and birds, and has a significant economic impact on the production of domestic animals as well as public health (Chen et al., 2011). Sarcocystis species have a life cycle with two hosts, herbivores as intermediate host and carnivores as definitive host. Human beings act as a definitive host for some speciesand get infected by eating raw or undercooked meat (Dhaliwal and Juyal, 2016). There have been only four validated species described in sheep: the non-pathogenic macroscopic S. gigantea and S. medusiformis transmitted by felids and the pathogenic microscopic S. tenella and S. arieticanis transmitted by canids (Dubey, 2016). In general, the Sarcocystis spp. transmitted by canids are more pathogenic than those transmitted by the feline. S. tenella can lead to acute sarcocystosis in uninfected sheep. Nonspecific infection symptoms including fever, anorexia, tachycardia, and anemia could be observed following infection. In acute sarcocystosis, the central nervous system will be involved, and it can cause encephalitis and encephalomyelitis and subsequently death in sheep (Uggla and Buxton, 1990). Neurological disorders with muscle weakness, trembling, ataxia followed by hind limb paresis or flaccid paralysis and recumbency are evident in clinical form (Radostits et al., 2007). In severe infection of esophagus muscle, esophageal dysfunction and regurgitation are expected. In some cases, cachexia, fever, anemia, in appetence, and alopecia were also reported (Titilincu et al., 2008).
Many studies about the distribution of sarcocystosis in slaughtered cattle, pigs, sheep, and horses have been carried out in different countries of Europe, North and South America, Asia, Australia, and Africa ( Dubey et al., 2015; Farhangpazhouh et al., 2020). The aim of this study was to determine the cause of a tumor-like tissue mass on the back of a 6-years-old ewe referred to Najafabad Veterinary Clinic, Isfahan, Iran.
Case History and Clinical Findings
A six-years-old native ewe with major clinical signs, including nasal discharge, enlarged superficial lymph nodes, and anorexia, was referred to a veterinary clinic in Najafabad, Isfahan province, Iran. Also, there was a round tumor-like mass about 23.2 cm × 3.5 cm in diameter on the back area (Figure 1). The mass was alopecic, and its surface was rough. At the first step, the mass was removed, but after two weeks, it was appeared again. A sample from the tissue formed on the back of ewe was isolated and placed in 10% formalin and 37% paraffin and then was stained with hematoxylin and eosin (H&E) for histopathological examination.
Under the light microscope, different sizes of Sarcocystis were seen in the subcutaneous muscle fibers (with 3.03 ± 0.44 µm in length), each surrounded by a thin layer of muscle fibers and contained banana-shaped bradyzoites. There was not any tissue reaction around the cysts (Figure 2). In addition to microscopic cysts, a macroscopic cyst with distinct anterior and posterior shape was seen in the subcutaneous muscles: The cyst containing bradyzoites had a thin wall and showed internal irregular septations (Figure 2). The epidermis overlying the cyst showed acanthosis, severe hyperkeratosis, and necrosis of epidermal cells (Figure 2). Hemorrhage and infiltration of inflammatory cells, mainly, neutrophils were also seen in the dermis (Figure 2).
In this study, a case of Sarcocystis spp. infection in an ewe with clinical symptoms of severe hyperkeratosis and superficial lymph nodes enlargement was reported. The enlargement of lymph nodes can occur because of the third generation of schizogony in the lymphocytes (Landsverk et al., 1978). Previously, in an experimental study with S. gigantea in rats (Al-Taei et al., 2011), hyperplasia of lymphoid tissue around bronchi have been reported. In another experimental study with S. gigantea in lamb, mild encephalitis, characterized by the presence of small microglial nodules scattered throughout the brain, was reported at 21-42 days post-inoculation. But, the bradyzoites have not been demonstrated in lesions.
In this case study, hyperkeratosis and sub-epidermal hemorrhages might have occured by the second schizogony generation in the vascular endothelial cells associated with Sarcocystis spp.(Hillyer et al., 1991). Since the Sarcocystis species was not identified in the present study, the cause of respiratory symptoms observed in the ewe may be due to other infectious diseases or sarcocystosis. In support of this, Bacci et al. (2016) have reported respiratory symptoms due to Sarcocystis tenella in young sheep (Bacci et al., 2016).
Moreover, neurological symptoms involving recumbency, weakness, ataxia, mild hyperesthesia, and dorsiflexion of the neck due to S. capracanis (goat pathogen) have been reported in sheep (Formisano et al., 2013).
Veronesi et al. (2020) have described the myofibers invasion in a horse infected by S. gigantea, a sheep-specific species, with low virulence in the original host. The horse was referred to the clinic of a veterinary surgeon, and the data suggested that the horse had an initial history of swelling of the right forelimb with fluid on the front of the carpus and edema spreading up the forearm. Subsequently, two firm lumps were found on the left pectoral muscle adjacent to the axilla of the left forelimb. The histologic examination of biopsies of the tumor-like tissue mass revealed multifocal granulomatous eosinophilic myositis associated with intact and degenerated encysted parasites, which were consistent with Sarcocystis spp. Finally, after amplifying and DNA sequencing of the 18S rRNA gene obtained from formalin-fixed, paraffin-embedded tissue blocks, S. gigantea was identified (Veronesi et al., 2020).
The authors would like to thank Dr. Iraj Karimi for preparing tissue sections and interpreting data.
Conflict of interest statement
There is no conflict of interest.