Evidence to support horses as natural intermediate hosts for Sarcocystis neurona

Inflammatory and Immune-Mediated Myopathies, What Do We Know?

Inflammatory myopathies or myositis encompass diseases characterized by the presence of inflammatory cellular infiltrates, mainly polymorphonuclear cells and/or lymphocytes, in muscle. This is in contrast to most forms of muscle disease characterized by myodegeneration that results in macrophage infiltration. Inflammatory myopathies could have infectious or noninfectious causes. Noninfectious causes consist of primary (genetic, autoimmune) or acquired immune-mediated disease. Focal, multifocal or diffuse, acute or recurrent forms of disease can occur. This article will mainly review immune-mediated myopathies in horses. Myositis directly caused by infection such as Clostridium spp and others will not be discussed here.

Sarcocystis in horses from Rio Grande do Sul, Brazil: Molecular identification of Sarcocystis bertrami and Sarcocystis neurona in muscle tissues

Horses are intermediate hosts of Sarcocystis spp. capable of forming cysts in their musculature. This study aimed to detect sarcocysts and investigate the presence of nucleic acids from Sarcocystis spp. in samples of striated muscles from horses in the State of Rio Grande do Sul, Brazil, necropsied at the Veterinary Pathology Laboratory of the Federal University of Santa Maria. A total of 108 samples were collected from 24 horses and examined through direct examination. Microscopic tissue cysts were observed in three samples: tongue (2) and esophagus (1) from two animals. Extractions were performed on the found cysts and tissues, even though sarcocystosis detection was not present. DNA samples were subjected to Nested-PCR using Tg18s primers, and the amplified products were subjected to Restriction Fragment Length Polymorphism (RFLP) using DdeI and HpaII enzymes. DNA belonging to Sarcocystis spp. was amplified in tissues from 91.7% (22/24) of the equines, and 67.6% (73/108) of the samples tested positive in the Nested-PCR reaction. The tissues with the highest detection frequency were: diaphragm 92.3% (12/13), gluteal muscle 77.2% (17/22), and esophagus 66.7% (4/6). In RFLP, Sarcocystis spp. was detected in 21 tissues from 11/22 equines, and cysts, identified through nucleotide sequencing, were determined to be S. bertrami. S. neurona was identified in 11 samples from 7/22 animals, with co-infection detected in 5/22 cases. The high detection rate indicates a concerning circulation of the protozoan, particularly the zoonotic S. bertrami found in all tissues, which are commonly exported for human consumption.

Equine Protozoal Myeloencephalitis

Advances in the understanding of equine protozoal myeloencephalitis (EPM) are reviewed. It is now apparent that EPM can be caused by either of 2 related protozoan parasites, Sarcocystis neurona and Neospora hughesi, although S neurona is the most common etiologic pathogen. Horses are commonly infected, but clinical disease occurs only infrequently; the factors influencing disease occurrence are not well understood. Epidemiologic studies have identified risk factors for the development of EPM, including the presence of opossums and prior stressful health-related events. Attempts to reproduce EPM experimentally have reliably induced antibody responses in challenged horses, but have not consistently produced neurologic disease. Diagnosis of EPM has improved by detecting intrathecal antibody production against the parasite. Sulfadiazine/pyrimethamine (ReBalance) and the triazine compounds diclazuril (Protazil) and ponazuril (Marquis) are effective anticoccidial drugs that are now available as FDA-approved treatments for EPM.

Sarcocystis neurona Transmission from Opossums to Marine Mammals in the Pacific Northwest

Increasing reports of marine mammal deaths have been attributed to the parasite Sarcocystis neurona. Infected opossums, the only known definitive hosts, shed S. neurona sporocysts in their feces. Sporocysts can contaminate the marine environment via overland runoff, and subsequent ingestion by marine mammals can lead to fatal encephalitis. Our aim was to determine the prevalence of S. neurona in opossums from coastal areas of Washington State (USA) and to compare genetic markers between S. neurona in opossums and marine mammals. Thirty-two road-kill opossums and tissue samples from 30 stranded marine mammals meeting inclusion criteria were included in analyses. Three opossums (9.4%) and twelve marine mammals (40%) were confirmed positive for S. neurona via DNA amplification at the ITS1 locus. Genetic identity at microsatellites (sn3, sn7, sn9) and the snSAG3 gene of S. neurona was demonstrated among one harbor porpoise and two opossums. Watershed mapping further demonstrated plausible sporocyst transport pathways from one of these opossums to the location where an infected harbor porpoise carcass was recovered. Our results provide the first reported link between S. neurona genotypes on land and sea in the Pacific Northwest, and further demonstrate how terrestrial pathogen pollution can impact the health of marine wildlife.

Molecular detection of Sarcocystis neurona in cerebrospinal fluid from 210 horses with suspected neurologic disease

An ante-mortem diagnosis of equine protozoal myeloencephalitis (EPM) is presently based on clinical presentation, immunodiagnostics performed on serum and cerebrospinal fluid (CSF), and ruling out other neurological disorders. Molecular techniques introduce a novel and promising approach for the detection of protozoal agents in CSF. Hypothesizing that real-time PCR (rtPCR) can be a useful complement to EPM diagnostics, 210 CSF samples from horses suspected of neurological disease with EPM included as a differential diagnosis were tested using rtPCR to detect Sarcocystis neurona DNA and immunodiagnostics targeting antibodies against the same pathogen, performed on serum and CSF samples. Molecular and immunological results were compared with respect to origin of the horse, time of the year, signalment, clinical signs and treatment history. Twenty-five horses tested positive in CSF for S. neurona by rtPCR only, while 30 horses had intrathecally-derived antibodies to S. neurona only (serum to CSF ratio ≤ 64 by indirect fluorescent antibody test - IFAT), and 13 horses tested rtPCR-positive in CSF with evidence of intrathecally-derived antibodies to S. neurona. Previous treatment for EPM was the only variable presenting statistical difference between the two testing modalities, highlighting that animals with history of anti-protozoal treatment were more likely to test positive solely in IFAT, while horses without treatment were more likely to test positive by rtPCR only. The results support the use of molecular diagnosis for EPM caused by S. neurona as a complement to immunodiagnostics. The use of rtPCR in CSF for the detection of S. neurona may improve the diagnostic work-up of neurologic disease suspected horses, especially in animals without previous anti-protozoal treatment.

Antibodies against Apicomplexa protozoa and absence sarcocysts in heart tissues from horses in southern Brazil

Abstract Sarcocystis spp., Neospora spp., and Toxoplasma gondii are Apicomplexa protozoa that can infect horses. This study aimed to investigate the occurrence of antibodies against Sarcocystis spp., Neospora spp., and T. gondii in horses slaughtered in southern Brazil. The presence of histological lesions, tissue cysts, and Sarcocystis spp. DNA in the hearts of these horses was also investigated. A total of 197 paired serum and heart samples were evaluated by serology and direct microscopic examination; 50 of these samples were subjected to histopathological and PCR analyses. Antibodies against at least one of the protozoa were detected in 146 (74.1%) of the serum samples. The frequencies of positive serology were: 36% (71/197) against Sarcocystis spp., 39.1% (77/197) against Neospora spp., and 47.2% (93/197) against T. gondii. No cysts, Sarcocystis spp. DNA, or histopathological lesions were observed in myocardial tissue samples. The frequencies of antibody seropositivity against Sarcocystis spp., Neospora spp., and T. gondii showed that horses are frequently infected by these parasites in southern Brazil. The absence of sarcocysts in horse tissues is compatible with their role as aberrant/accidental hosts in the life cycle of Sarcocystis spp..

Therapeutics for Equine Protozoal Myeloencephalitis

Equine protozoal myeloencephalitis is an infectious disease of the central nervous system caused by Sarcocystis neurona or Neospora hughesi. Affected horses routinely present with progressive and asymmetrical neurologic deficits. The diagnosis relies on the presence of neurologic signs, ruling out other neurologic disorders, and the detection of intrathecally derived antibodies to either S neurona and/or N hughesi. Recommended treatment is use of an FDA-approved anticoccidial drug formulation. Medical and supportive treatment is provided based on the severity of neurologic deficits and complications. This article focuses on recent data related to diagnosis, pharmacologic treatment, and prevention.

Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment, and Prevention

Equine protozoal myeloencephalitis (EPM) remains an important neurologic disease of horses. There are no pathognomonic clinical signs for the disease. Affected horses can have focal or multifocal central nervous system (CNS) disease. EPM can be difficult to diagnose antemortem. It is caused by either of 2 parasites, Sarcocystis neurona and Neospora hughesi, with much less known about N. hughesi. Although risk factors such as transport stress and breed and age correlations have been identified, biologic factors such as genetic predispositions of individual animals, and parasite‐specific factors such as strain differences in virulence, remain largely undetermined. This consensus statement update presents current published knowledge of the parasite biology, host immune response, disease pathogenesis, epidemiology, and risk factors. Importantly, the statement provides recommendations for EPM diagnosis, treatment, and prevention.

Sarcocystis fayeri in skeletal muscle of horses with neuromuscular disease

Recent reports of Sarcocystis fayeri-induced toxicity in people consuming horse meat warrant investigation on the prevalence and molecular characterization of Sarcocystis spp. infection in horses. Sarcocysts in skeletal muscle of horses have been commonly regarded as an incidental finding. In this study, we investigated the prevalence of sarcocysts in skeletal muscle of horses with neuromuscular disease. Our findings indicated that S. fayeri infection was common in young mature horses with neuromuscular disease and could be associated with myopathic and neurogenic processes. The number of infected muscles and number of sarcocysts per muscle were significantly higher in diseased than in control horses. S. fayeri was predominantly found in low oxidative highly glycolytic myofibers. This pathogen had a high glycolytic metabolism. Common clinical signs of disease included muscle atrophy, weakness with or without apparent muscle pain, gait deficits, and dysphagia in horses with involvement of the tongue and esophagus. Horses with myositis were lethargic, apparently painful, stiff, and reluctant to move. Similar to humans, sarcocystosis and cardiomyopathy can occur in horses. This study did not establish causality but supported a possible association (8.9% of cases) with disease. The assumption of Sarcocysts spp. being an incidental finding in every case might be inaccurate.

Sarcocystis spp. Infection in two Red Panda Cubs (Ailurus fulgens)

Two neonatal male red panda (Ailurus fulgens) littermates were submitted for necropsy examination. One animal was found dead with no prior signs of illness; the other had a brief history of laboured breathing. Post-mortem examination revealed disseminated protozoal infection. To further characterize the causative agent, transmission electron microscopy (TEM), immunohistochemistry (IHC), polymerase chain reaction (PCR) and amplification and nucleic acid sequencing were performed. IHC was negative for Toxoplasma gondii and Neospora caninum, but was positive for a Sarcocystis spp. TEM of cardiac muscle and lung revealed numerous intracellular apicomplexan protozoa within parasitophorous vacuoles. PCR and nucleic acid sequencing of partial 18S rRNA and the internal transcribed spacer (ITS)-1 region confirmed a Sarcocystis spp. that shared 99% sequence homology to Sarcocystis neurona and Sarcocystis dasypi. This represents the first report of sarcocystosis in red pandas. The histopathological, immunohistochemical, molecular and ultrastructural findings are supportive of vertical transmission resulting in fatal disseminated disease.

An update on Sarcocystis neurona infections in animals and equine protozoal myeloencephalitis (EPM)

Equine protozoal myeloencephalitis (EPM) is a serious disease of horses, and its management continues to be a challenge for veterinarians. The protozoan Sarcocystis neurona is most commonly associated with EPM. S. neurona has emerged as a common cause of mortality in marine mammals, especially sea otters (Enhydra lutris). EPM-like illness has also been recorded in several other mammals, including domestic dogs and cats. This paper updates S. neurona and EPM information from the last 15 years on the advances regarding life cycle, molecular biology, epidemiology, clinical signs, diagnosis, treatment and control.

Equine protozoal myeloencephalitis

Equine protozoal myeloencephalitis (EPM) can be caused by either of 2 related protozoan parasites, Sarcocystis neurona and Neospora hughesi, although S. neurona is the most frequent etiologic pathogen. Horses are commonly infected, but clinical disease occurs infrequently; the factors influencing disease occurrence are not well understood. Risk factors for the development of EPM include the presence of opossums and prior stressful health-related events. Attempts to reproduce EPM experimentally have reliably induced antibody responses in challenged horses but have not consistently produced acute neurologic disease. Diagnosis and options for treatment of EPM have improved over the past decade.

Serum antibodies from a subset of horses positive for Babesia caballi by competitive enzyme-linked immunosorbent assay demonstrate a protein recognition pattern that is not consistent with infection

Tick-borne pathogens that cause persistent infection are of major concern to the livestock industry because of transmission risk from persistently infected animals and the potential economic losses they pose. The recent reemergence of Theileria equi in the United States prompted a widespread national survey resulting in identification of limited distribution of equine piroplasmosis (EP) in the U.S. horse population. This program identified Babesia caballi-seropositive horses using rhoptry-associated protein 1 (RAP-1)-competitive enzyme-linked immunosorbent assay (cELISA), despite B. caballi being considered nonendemic on the U.S. mainland. The purpose of the present study was to evaluate the suitability of RAP-1-cELISA as a single serological test to determine the infection status of B. caballi in U.S. horses. Immunoblotting indicated that sera from U.S. horses reacted with B. caballi lysate and purified B. caballi RAP-1 protein. Antibody reactivity to B. caballi lysate was exclusively directed against a single ∼50-kDa band corresponding to a native B. caballi RAP-1 protein. In contrast, sera from experimentally and naturally infected horses from regions where B. caballi is endemic bound multiple proteins ranging from 30 to 50 kDa. Dilutions of sera from U.S. horses positive by cELISA revealed low levels of antibodies, while sera from horses experimentally infected with B. caballi and from areas where B. caballi is endemic had comparatively high antibody levels. Finally, blood transfer from seropositive U.S. horses into naive horses demonstrated no evidence of B. caballi transmission, confirming that antibody reactivity in cELISA-positive U.S. horses was not consistent with infection. Therefore, we conclude that a combination of cELISA and immunoblotting is required for the accurate serodiagnosis of B. caballi.

Exposure to Sarcocystis spp. in horses from Spain determined by Western blot analysis using Sarcocystis neurona merozoites as heterologous antigen

Horses serve as an intermediate host for several species of Sarcocystis, all of which utilize canids as the definitive host. Sarcocystis spp. infection and formation of latent sarcocysts in horses often appears to be subclinical, but morbidity can occur, especially when the parasite burden is large. A serological survey was conducted to determine the presence of antibodies against Sarcocystis spp. in seemingly healthy horses from the Galicia region of Spain. Western blot analyses using Sarcocystis neurona merozoites as heterologous antigen suggested greater than 80% seroprevalance of Sarcocystis spp. in a sample set of 138 horses. The serum samples were further tested with enzyme-linked immunosorbent assays (ELISAs) based on recombinant S. neurona-specific surface antigens (rSnSAGs). As expected for horses from the Eastern Hemisphere, less than 4% of the serum samples were positive when analyzed with either the rSnSAG2 or the rSnSAG4/3 ELISAs. An additional 246 horses were tested using the rSnSAG2 ELISA, which revealed that less than 3% of the 384 samples were seropositive. Collectively, the results of this serologic study suggested that a large proportion of horses from this region of Spain are exposed to Sarcocystis spp. Furthermore, the anti-Sarcocystis seroreactivity in these European horses could be clearly distinguished from anti-S. neurona antibodies using the rSnSAG2 and rSnSAG4/3 ELISAs.

Molecular characterization of five Sarcocystis species in red deer ( Cervus elaphus), including Sarcocystis hjorti n. sp., reveals that these species are not intermediate host specific

Muscle tissue from 37 red deer from Norway was examined for sarcocysts. Sarcocysts from 2 reindeer were obtained for comparative studies. Cysts were excised and morphologically classified by light microscopy, scanning electron microscopy, and DNA sequence analysis. Five Sarcocystis species, Sarcocystis hjorti n. sp., Sarcocystis hardangeri, Sarcocystis ovalis, Sarcocystis rangiferi, and Sarcocystis tarandi, were found. All 5 species have previously been identified from either reindeer or moose by their sarcocyst morphology and/or ssu rRNA gene sequence. S. hjorti was the most prevalent species. Multiple variants of the ssu rRNA gene and the first internal transcribed spacer were found in S. rangiferi and S. tarandi from both red deer and reindeer. Phylogenetic analyses indicated that S. tarandi occurs in both red deer and reindeer, but it could not be clearly demonstrated whether the sequence variation within S. rangiferi between hosts was due to different paralogues or/and different species. DNA sequencing was necessary for definitive species identification, since the hair-like protrusions on the cysts of S. hjorti were not always recognizable by light microscopy and since different cervids harbour Sarcocystis species with highly similar cyst morphology of which at least some are not intermediate host specific.

Ultrastructural and molecular confirmation of the development of Sarcocystis neurona tissue cysts in the central nervous system of southern sea otters (Enhydra lutris nereis)

In 2004, three wild sea otters were diagnosed with putative Sarcocystis neurona-associated meningoencephalitis by histopathology and immunohistochemistry. Schizonts, free merozoites and tissue cysts were observed in the brains of all three infected animals. Tissue cysts walls from sea otter 1 (SO1) stained positively using anti-S. neurona polyclonal antiserum. However, positive staining does not preclude infection by closely related or cross-reactive tissue cyst-forming coccidian parasites. Two immature tissue cysts in the brain of SO1 were examined using transmission electron microscopy. Ultrastructural features included cyst walls with thin villous projections up to 1 microm long with tapered ends and a distinctive, electron-dense outer lining layer composed of linearly-arranged, semi-circular structures with a "hobnailed" surface contour. Small numbers of microtubules extended down through the villi into the underlying granular layer. Metrocytes were short and plump with an anterior apical complex, 22 sub-pellicular microtubules, numerous free ribosomes and no rhoptries. Some metrocytes appeared to be dividing, with two adjacent nuclear profiles. Collectively these ultrastructural features were compatible with developing protozoal cysts and were similar to prior descriptions of S. neurona tissue cysts. Panspecific 18S rDNA primers were utilized to identify protozoa infecting the brains of these otters and DNA amplification and additional sequencing at the ITS1 locus confirmed that all three otters were infected with S. neurona. No other Sarcocystis spp. were detected in the brains or skeletal muscles of these animals by immunohistochemistry or PCR. We believe this is the first ultrastructural and molecular confirmation of the development of S. neurona tissue cysts in the CNS of any animal.

Sarcocystis in moose (Alces alces): molecular identification and phylogeny of six Sarcocystis species in moose, and a morphological description of three new species

Muscle tissues from 34 moose from Southeastern Norway and two moose from Canada were examined. Sarcocysts were excised and morphologically classified by light microscopy, and some cysts were further examined by scanning electron microscopy or DNA amplification and sequencing at the small subunit (ssu) rRNA gene. In Norwegian moose, three sarcocyst types were recognized, yet five Sarcocystis species were found by sequence analysis. New names were proposed for three species which could be characterised by both morphological and molecular methods, i.e., Sarcocystis alces, Sarcocystis ovalis, and Sarcocystis scandinavica. S. alces was the most prevalent species, whereas S. scandinavica and the two unnamed species were rare and might either use another principal intermediate host or a rare definitive host. The five species in Norwegian moose were different from Sarcocystis alceslatrans isolated from a Canadian moose. Phylogenetic analyses based on complete ssu rRNA gene sequences revealed a close relationship between the six Sarcocystis species from moose and species from reindeer and Sika deer. We conclude that molecular methods are necessary for unequivocal species identification, as different cervid hosts harbour morphologically indistinguishable sarcocysts.

Diagnosis and treatment of Sarcocystis neurona in a captive harbor seal (Phoca vitulina)

A captive harbor seal (Phoca vitulina) presented with partial anorexia, ataxia, and head bobbing, which progressed to complete anorexia, lethargy, and persistent whole-body intention tremors within several days. Response to treatment with ponazuril, serology, and cerebrospinal fluid analysis supported a diagnosis of Sarcocystis neurona. Analysis of serum levels for ponazuril indicated that therapeutic levels could be achieved at a dosage of 5 mg/kg p.o. s.i.d., whereas clinical response was improved at a dosage of 10 mg/kg. Several months after initiation of antiprotozoal therapy, the neurologic signs resolved, although rare intermittent tremors were seen with significant exertion.

Investigation of SnSPR1, a novel and abundant surface protein of Sarcocystis neurona merozoites

An expressed sequence tag (EST) sequencing project has produced over 15,000 partial cDNA sequences from the equine pathogen Sarcocystis neurona. While many of the sequences are clear homologues of previously characterized genes, a significant number of the S. neurona ESTs do not exhibit similarity to anything in the extensive sequence databases that have been generated. In an effort to characterize parasite proteins that are novel to S. neurona, a seemingly unique gene was selected for further investigation based on its abundant representation in the collection of ESTs and the predicted presence of a signal peptide and glycolipid anchor addition on the encoded protein. The gene was expressed in E. coli, and monospecific polyclonal antiserum against the recombinant protein was produced by immunization of a rabbit. Characterization of the native protein in S. neurona merozoites and schizonts revealed that it is a low molecular weight surface protein that is expressed throughout intracellular development of the parasite. The protein was designated Surface Protein 1 (SPR1) to reflect its display on the outer surface of merozoites and to distinguish it from the ubiquitous SAG/SRS surface antigens of the heteroxenous Coccidia. Interestingly, infection assays in the presence of the polyclonal antiserum suggested that SnSPR1 plays some role in attachment and/or invasion of host cells by S. neurona merozoites. The work described herein represents a general template for selecting and characterizing the various unidentified gene sequences that are plentiful in the EST databases for S. neurona and other apicomplexans. Furthermore, this study illustrates the value of investigating these novel sequences since it can offer new candidates for diagnostic or vaccine development while also providing greater insight into the biology of these parasites.

Molecular genetic transfection of the coccidian parasite Sarcocystis neurona

Sarcocystis neurona is an apicomplexan parasite that is the major cause of equine protozoal myeloencephalitis (EPM). The biology of this pathogen remains poorly understood in part due to unavailability of molecular genetic tools. Hence, with an objective to develop DNA transfection capabilities for S. neurona, the 5' flanking region of the SnSAG1 gene was isolated from a genomic library and used to construct expression plasmids. In transient assays, the reporter molecules beta-galactosidase (beta-gal) and yellow fluorescent protein (YFP) could be detected in electroporated S. neurona, thereby confirming the feasibility of transgene expression in this organism. Stable transformation of S. neurona was achieved using a mutant dihydrofolate reductase thymidylate synthase (DHFR-TS) gene of Toxoplasma gondii that confers resistance to pyrimethamine. This selection system was used to create transgenic S. neurona that stably express beta-gal and YFP. As shown in this study, these transgenic clones can be useful for analyzing growth rate of parasites in vitro and for assessing drug sensitivities. More importantly, the DNA transfection methods described herein should greatly facilitate studies examining intracellular parasitism by this important coccidian pathogen.

Genetic variation among isolates of Sarcocystis neurona, the agent of protozoal myeloencephalitis, as revealed by amplified fragment length polymorphism markers

Sarcocystis neurona causes serious neurological disease in horses and other vertebrates in the Americas. Based on epidemiological data, this parasite has recently emerged. Here, the genetic diversity of Sarcocystis neurona was evaluated using the amplified fragment length polymorphism (AFLP) method. Fifteen S. neurona taxa from different regions collected over the last 10 years were used; six isolates were from clinically diseased horses, eight isolates were from wild-caught opossums (Didelphis virginiana), and one isolate was from a cowbird (Molothrus ater). Additionally, four outgroup taxa were also fingerprinted. Nine primer pairs were used to generate AFLP patterns, with a total number of amplified fragments ranging from 30 to 60, depending on the isolate and primers tested. Based on the presence/absence of amplified AFLP fragments and pairwise similarity values, all the S. neurona isolates tested were clustered in one monophyletic group. No significant correlation could be found between genomic similarity and host origin of the S. neurona isolates. AFLP revealed significant intraspecific genetic variations, and S. neurona appeared as a highly variable species. Furthermore, linkage disequilibrium analysis suggested that S. neurona populations within Michigan have an intermediate type of population structure that includes characteristics of both clonal and panamictic population structures. AFLP is a reliable molecular technique that has provided one of the most informative approaches to ascertain phylogenetic relationships in S. neurona and its closest relatives, allowing them to be clustered by relative similarity using band matching and unweighted pair group method with arithmetic mean analysis, which may be applicable to other related protozoal species.