Anti-Sarcocystis Antibodies in Lambs Deprived of Colostrum

Abstract

Introduction

The objective of this study was to evaluate the presence of anti-Sarcocystis spp. specific IgG antibodies in serum samples from precolostral lambs to determine the occurrence of transplacental transmission of Sarcocystis spp. in sheep.

Methods

Blood samples were collected from 80 ewes and their respective lambs, immediately after lambing and before colostrum ingestion, respectively. The presence of anti-Sarcocystis spp. IgG was evaluated in serum samples using the indirect fluorescent antibody test (IFAT). Positive samples of the lambs were submitted to titration and IFAT to detect anti-T. gondii and anti-N. caninum specific IgG.

Results

Anti-Sarcocystis spp. IgG was detected in 62.5% of the ewes (50/80) and in 4% of the lambs of the seropositive ewes (2/50). None of the lambs from seronegative ewes were positive. The final titers of the positive lambs were 80. No cross reaction was detected among the positive samples to anti-Sarcocystis spp., anti-N. caninum, and anti-T. gondii IgG. The detection of anti-Sarcocystis spp. antibodies in serum samples of lambs deprived of colostrum suggests transplacental transmission of infection. Thus, the vertical transmission may be an alternative route of infection of Sarcocystis spp. also in sheep. Further studies are warranted to confirm transplacental transmission in sheep and to explain the importance of this infection pathway.

Over a 100 species of the protozoon Sarcocystis are distributed worldwide infecting a wide range of domestic and wild animals [8]. The life cycle of this protozoan has definitive and intermediate hosts. The definitive hosts are usually the predators, such as felids, canids, and humans. Sexual reproduction occurs in the intestine of the definitive host and results in the excretion of oocysts in the feces [9]. Intermediate hosts (typically, herbivores) become infected by ingesting the water or food contaminated with oocysts excreted from the definitive host [8]. Sheep can be infected by at least four species of Sarcocystis. S. tenella and S. arietcanis form microscopic cysts (microcysts) in muscles and have canids as the definitive host. S. gigantea and S. medusiformis form macroscopic cysts (macrocysts) in muscles and have the domestic cat (Felis catus) as the definitive host [8]. In studies on slaughtered sheep in Rio Grande do Sul, microcysts were found in 76.2% of myocardial [22], and both macrocysts and microcysts were found in 96.1% of muscle tissue [16].

Sarcocystosis usually presents a subclinical course in small ruminants. Clinical infection can result in anemia, weight loss, and apathy. Other signs associated with the central nervous system such as ataxia, paresis, myopathy, weakness, and death have been observed [8]. Sarcocystis spp. infection may eventually cause reproductive disorders [21] and macrocysts were related to condemnation of carcasses in slaughterhouses [15].

Some aspects of the life cycle of Sarcocystis spp. are well known; however, some routes of infection have not been investigated in small ruminants. Transplacental transmission has already been demonstrated in other Apicomplexa protozoa, such as Neospora caninum [6] and Toxoplasma gondii [3]. In sheep, the transplacental transmission rate of N. caninum and T. gondii is 70–90 [11] and 60–70% [24], respectively. Transplacental transmission of Sarcocystis spp. has been suggested in horse [1, 8] and cattle [17] but it has not been demonstrated in sheep.

The objective of this study was to evaluate the presence of anti-Sarcocystis spp. specific IgG antibodies in serum samples from precolostral lambs to determine the occurrence of transplacental transmission of Sarcocystis spp. in sheep.

This study was conducted in a sheep farm located in the west region of Rio Grande do Sul, a subtropical area in southern Brazil. Eighty ewes of breed Corriedale, Ideal, and Merino and their lambs were used in the experiment. All ewes gave birth to healthy lambs and 36.25% and 6.25% of the ewes had twins and triplets lambs, respectively. The sheep had contact with cats and dogs, and no previous reports of abortion were related. The perinatal death rate was 3.75%.

Blood samples were collected from the ewes and from their respective lambs, immediately after lambing and before colostrum ingestion, respectively. After blood collection, it was centrifuged at 250×g for 12 min to obtain the serum. Serum samples were frozen and stored until processing and tested using the indirect fluorescent antibody test (IFAT) for anti-Sarcocystis spp. IgG. Merozoites obtained from S. gigantea cysts were used as antigens. The serum samples were diluted in PBS at the dilution ratio of 1:40 [19]. An anti-sheep IgG fluorescein isothiocyanate conjugate (Sigma Bio Sciences, St. Louis, USA) was used at 1:500 dilution. Positive and negative serum samples were used as controls. Presence of complete peripheral fluorescence of merozoites was considered positive [4]. Positive samples of the lambs were submitted to titration and IFAT to detect anti-T. gondii and anti-N. caninum specific IgG according to [19].

All experimental practices involving animals were approved by the Ethics Committee for Animal Experimentation at Universidade Federal de Santa Maria (UFSM) (protocol number: 9246060418).

The occurrence of vertical transmission of Sarcocystis spp. infection was investigated by detecting antibodies in ewes and their respective lambs after lambing and prior to colostrum ingestion. Anti-Sarcocystis spp. IgG was detected in 62.5% of the ewes (50/80) and in 4% of the newborn lambs of the seropositive ewes (2/50). The final titers of the positive lambs were 80. None of the lambs from seronegative ewes were positive. No cross reaction was detected among the positive samples to anti- Sarcocystis spp., anti-N. caninum, and anti-T. gondii IgG.

The detection of anti-Sarcocystis spp. antibody in serum samples from lambs deprived of colostrum suggests the exposure of the fetus to antigens of the protozoan during gestation, and therefore transplacental transmission of the infection. No studies have been conducted on the intrauterine exposure to Sarcocystis spp. in sheep. In horse studies, anti-Sarcocystis antibodies were detected in foals (7.4%) deprived of colostrum [1]. IFAT is the most frequently used test to detect anti-protozoa IgG and is considered the gold standard for the diagnosis of these infections [7, 13].

In cattle, cross-reactivity by IFAT among S. cruzi, N. caninum, and T. gondii is negligible [5, 10]. Moreover, Moré et al. [17] concluded that serology using IFAT is a suitable method to diagnose S. cruzi, T. gondii, and N. caninum infections in cattle because of its specificity. However, no studies have been conducted to evaluate cross-reactivity among the Apicomplexa protozoa in sheep using serological tests, and this is important because, as it was mentioned, Sarcocystis spp. in sheep are different from those in cattle [10].

The proportion of lambs in which anti-Sarcocystis spp. antibodies were detected as a result of possible endogenous transmission of infection was relatively low (4%). The genus Sarcocystis belongs to the phylum Apicomplexa. In this phylum, there are other genera, such as N. caninum [6] and T. gondii [3], that efficiently use the endogenous transmission pathway. Therefore, the possibility of vertical transmission of infection by Sarcocystis spp. was expected.

The occurrence of anti-Sarcocystis spp. antibody in sheep has not been commonly reported [8]. In the present study, the detection rate of anti-Sarcocystis spp. antibody was 62.5% by IFAT. In Spain, the frequency of detection of anti-Sarcocystis spp. antibody in sheep using the indirect hemagglutination (IHA) technique was 88% [20]. Most studies detected microcysts in the musculature through direct examination or molecular techniques, such as polymerase chain reaction (PCR). The frequency of detection of microcysts in muscle tissue in Brazil ranges from 76.2 to 96.1% [2, 22] and in the world from 70 to 100% [12, 14, 18, 23].

The Sarcocystis spp. infection has a high prevalence and large distribution because of exogenous transmission [8]. Based on the low frequency of antibody detection in precolostral lambs in this study, the endogenous transmission could be an alternative route of infection, but not the most important one. Although it has not been investigated in this study, the exogenous route seems to have greater efficiency in transmission.

The detection of anti-Sarcocystis spp. antibody in serum samples from lambs deprived of colostrum suggests the occurrence of transplacental transmission of the infection. The vertical transmission may be an alternative route of infection used by Sarcocystis spp. in sheep. Further studies with more specific serology test are necessary to confirm transplacental transmission of Sarcocystis spp in sheep.

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Acknowledgements

The authors are grateful to the Coordination for the Improvement of Higher Education Personnel (CAPES), Brazil, for the financial support.

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Correspondence to Camila Encarnação Minuzzi.

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Minuzzi, C.E., de Souza Rodrigues, F., Marques, C.B. et al. Anti-Sarcocystis Antibodies in Lambs Deprived of Colostrum. Acta Parasit. 65, 256–258 (2020). https://doi.org/10.2478/s11686-019-00114-z

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Keywords

  • Sarcocystis
  • Precolostral serology
  • IFAT
  • Sheep
  • Transplacental transmission
  • Congenital transmission