Introduction

Sarcocystis spp. are intracellular protozoan parasites (Apicomplexa: Sarcocystidae) with an obligatory prey-predator, two-host life cycle. There are two types of hosts involved: the intermediate host (IH), which is infected through the consumption of food or water contaminated with sporocysts, and the definitive host (DH), which is infected by ingesting tissues containing sarcocysts (Dubey et al. 2015).

Sarcocystis spp. are widespread parasites that infect mammals, birds, and reptiles. Several species of Sarcocystis have evolved to be able to infect multiple hosts (Shams et al. 2022). Among these, the most prevalent are S. cruzi and S. hominis, which infect cattle, and S. gigantea and S. tenella, which infect sheep (Shams et al. 2022). Other species, such as S. neurona, infect horses and cause equine protozoal myeloencephalitis (EPM) (Dubey et al. 2000), while S. falcatula is known to infect birds (Gondim et al. 2019).

Felines can act as either the IH or DH for Sarcocystis spp.: they are known DHs of various Sarcocystis species, such as S. gigantea, S. medusiformis, S. hirsuta, S. porcifelis, S. moulei, S. bovifelis (Dubey et al. 2020; Gjerde et al. 2016a, b; Heydorn et al. 1975), S. sinensis (Gjerde et al. 2016a), and S. bovini (Gjerde et al. 2016b), and can also act as the IH of S. felis (Dubey et al. 1992) and S. neurona (Cheadle et al. 2001; Turay et al. 2002). Domestic cats (Felis domesticus) have the ability to act as either the IH or DH for S. sinensis (Gjerde et al. 2016a) and have also been described as an IH of S. neurona which is the causative agent of EPM in horses (Dubey et al. 2015). However, studies on the role of domestic cats in Sarcocystis epidemiology and Sarcocystis spp. detection and characterization, particularly in Brazil, are scarce.

Therefore, the objective of this study was to detect the presence of anti-Sarcocystis spp. antibodies in serum samples from domestic cats.

Materials and methods

Serum samples

In total, 497 blood samples were collected from cats that received veterinary assistance at the Hospital Veterinário Universitário (HVU) of Universidade Federal de Santa Maria (UFSM) between October 2018 and May 2019. The blood samples were drawn from the cats during clinical evaluation. After blood count analysis, the samples were centrifuged at 3400 rpm for 4 min, and the serum was collected and stored at − 20 °C. The serum samples were analyzed for the presence of antibodies against Sarcocystis spp. at the Laboratório de Doenças Parasitárias (LADOPAR) in UFSM.

Indirect immunofluorescence antibody test

Detection of IgGs against anti-Sarcocystis spp. in the cat serum samples was performed using indirect immunofluorescence antibody test (IFAT). Slides containing fixed Sarcocystis bradyzoites, which were obtained from bovine hearts, were used to perform IFAT. The bradyzoites were diluted in phosphate-buffered solution (PBS, pH 7.4) at a final concentration of 1.5–2.0 × 103 bradyzoites/mL. Approximately 20 µL of this solution was added to each well on specific IFAT slides, dried at room temperature, and fixed with methanol.

Sera were diluted at 1:50 in PBS (pH 7.4) (Hsu et al. 2010), placed in wells on the slide, and incubated at 37 °C for 50 min in a humid chamber. The slides were washed with PBS, followed by an incubation at 37 °C for 50 min in a humid chamber with anti-cat IgG antibody conjugated with fluorescein (Sigma-Aldrich Inc., St. Louis, MO, USA) diluted at 1:200 in PBS. The slides were washed again, mounted with mounting fluid (glycerol/PBS, 50:50) and a cover slip, and then examined under a fluorescent microscope at 400 × magnification. The samples were considered positive at a 1:50 dilution. Sarcocystis spp.–positive (naturally infected) and Sarcocystis-negative cat sera were used as the positive and negative controls, respectively.

Results and discussions

Anti-Sarcocystis spp. antibodies were detected in 24 cat serum samples with an antibody detection frequency of 4.82% (24/497). Few studies have investigated the serostatus of Brazilian domestic cats with regard to the genus Sarcocystis (Dubey et al. 2002; Meneses et al. 2014; Koch et al. 2019). This is the first study to detect anti-Sarcocystis spp. antibodies in domestic cats in southern Brazil. However, several studies have reported the detection of antibodies against S. neurona in cats (Meneses et al. 2014), and in some studies, the detection frequency was similar to that in the present study. Furthermore, the detection frequencies of antibodies against S. neurona detected by Meneses (2014) and Koch et al. (2019) were 4% and 5%, respectively, similar to the results obtained in our study.

The IFAT test contained bradyzoites from an undetermined species of Sarcocystis that infect cattle. However, because cross-reactions among Sarcocystis species occur (Ferreira et al. 2020), these using bovine-derived bradyzoite can still be used for the detection of anti-Sarcocystis antibodies in cat serum samples. Because of these cross-reactions that allow the use of undetermined species of Sarcocystis serological detection, the results obtained are related to anti-Sarcocystis spp. antibodies at the genus level.

Sarcocystis infection in cats is usually not associated with clinical signs. However, the detection of anti-Sarcocystis spp. IgGs in cat serum confirms that natural infection by Sarcocystis does occur in domestic cats and is capable of a specific and quantifiable immune response. Therefore, domestic cats represent an important host involved in the Sarcocystis life cycle. This information is especially valuable, as cats are present in both urban and rural areas, where they circulate indoors and outdoors, while coming into close contact with humans and other animals, such as horses. In this way, cats can act as a widespread source of Sarcocystis infection, both as an IH and DH, causing disease in various other animals, such as EPM in horses.

Conclusion

Anti-Sarcocystis spp. antibodies were detected in serum samples of domestic cats from a region in southern Brazil. To the best of our knowledge, this is the first study to detect antibodies against the genus Sarcocystis in Brazilian cats. In addition, our results confirm that natural infection by Sarcocystis does occur in domestic cats, and strongly support the participation of cats as hosts in the Sarcocystis life cycle.