Clinical Diagnosis of Equine Protozoal Myeloencephalitis (EPM)*

Furr, Martin; MacKay, Robert J.; Granstrom, David E.; Schott, Harold C.; Andrews, Frank M.

doi:10.1111/j.1939-1676.2002.tb02398.x

Cited by 60 publications

(21 citation statements)

References 6 publications

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“…Because of these discrepancies, a recent consensus statement by the American College of Veterinary Internal Medicine does not recommend the use of AQ or IgG index for the diagnosis of EPM. 10 Potential limitations of the current study include the relatively small number of horses in the higher serum IFAT groups (S. neurona $ 640, N. hughesi $ 160). Several horses with high serum IFAT titers (S. neurona $ 640, n 5 2 horses; N. hughesi $ 320; n 5 7 horses) had repeated blood samples taken and used to contaminate CSF; however, when these samples were excluded from analysis, statistical findings were unchanged.…”

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confidence: 95%

“…At this time, definitive diagnosis of EPM relies on immunohistopathological examination of neural tissue at postmortem. 10 Until recently, the Western blot (WB) test was the standard diagnostic test used for serologic surveys and the clinical diagnosis of EPM caused by S. neurona. When performed on serum, the overall sensitivity and specificity of the WB for the detection of clinical EPM were estimated at 80% and 38%, respectively, for horses with signs of neurologic disease.…”

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confidence: 99%

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Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies againstSarcocystis NeuronaandNeospora Hughesi

et al. 2007

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Abstract. The purpose of this study was to determine the effect of blood contamination of cerebrospinal fluid (CSF) on the results of indirect fluorescent antibody tests (IFATs) for Sarcocystis neurona and Neospora hughesi. The in vitro study used antibody-negative CSF collected from non-neurologic horses immediately after euthanasia and blood samples from 40 healthy horses that had a range of IFAT antibody titers against S. neurona and N. hughesi. Serial dilutions of whole blood were made in seronegative CSF to generate bloodcontaminated CSF with red blood cell (RBC) concentrations ranging from 10 to 100,000 RBCs/ml. The bloodcontaminated CSF samples were then tested for antibodies against both pathogens using IFAT. Blood contamination of CSF had no detectable effect on IFAT results for S. neurona or N. hughesi at any serologic titer when the RBC concentration in CSF was ,10,000 RBCs/ml. At concentrations of 10,000-100,000 RBCs/ ml of CSF, positive CSF results (IFAT titer $5) for S. neurona and N. hughesi were detected only when the corresponding serum titers were $160 and $80, respectively. The IFAT performed on CSF is reliable for testing horses for equine protozoal myeloencephalitis caused by S. neurona or N. hughesi, even when blood contamination causes the RBC concentration in CSF to be up to 10,000 RBCs/ml.Key words: Equine protozoal myeloencephalitis; indirect fluorescent antibody test.Equine protozoal myeloencephalitis (EPM) is caused by infection of the central nervous system of horses and ponies with the protozoan parasites Sarcocystis neurona, 7 and, less commonly, Neospora spp., 3,11,13 particularly Neospora hughesi.2,8,14 Equine protozoal myeloencephalitis is often a progressively debilitating disease that induces clinical signs that may include weakness, ataxia, loss of proprioception, incoordination, muscle wasting, behavioral changes, and death.9,12 Antemortem diagnosis of EPM is based upon a thorough neurologic examination, evaluation of serum and cerebrospinal fluid (CSF) for the presence of antibodies to S. neurona and N. hughesi, and the elimination of other neurologic disorders. It is important to note that the presence of antibodies in serum indicates only exposure to, and not necessarily clinical infection with, the respective parasites. At this time, definitive diagnosis of EPM relies on immunohistopathological examination of neural tissue at postmortem. 10Until recently, the Western blot (WB) test was the standard diagnostic test used for serologic surveys and the clinical diagnosis of EPM caused by S. neurona. When performed on serum, the overall sensitivity and specificity of the WB for the detection of clinical EPM were estimated at 80% and 38%, respectively, for horses with signs of neurologic disease.4 Specificity of the WB test when used on CSF was estimated at 44%. 4 A serum indirect fluorescent antibody test (IFAT) was recently evaluated for the diagnosis of EPM caused by S. neurona by using an arbitrarily chosen cut-off serum titer of 80 for a positive test. When compared to th...

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confidence: 95%

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confidence: 99%

Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies againstSarcocystis NeuronaandNeospora Hughesi

et al. 2007

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“…Widespread equine exposure to S. neurona with subsequent antibody production in horses without central nervous system (CNS) infection confounds interpretation of serum titers. 4 Normal partitioning of serum antibodies across the blood-brain barrier (BBB) can lead to false positive results when only CSF is tested. 5 Previous recommendations included testing CSF rather than serum, 4 linking serum titers to posttest probabilities of infection, 6 and most recently, evaluating serum and CSF titers concurrently.…”

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confidence: 99%

Indirect Fluorescent Antibody Test and Surface Antigen ELISAs for Antemortem Diagnosis of Equine Protozoal Myeloencephalitis

Johnson

Morrow

Sweeney

2013

Veterinary Internal Medicne

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Background: Recent research suggests that serum : CSF titer ratios could provide the most accurate antemortem diagnosis of equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona.Objectives: The purpose of this study was to assess the utility of two commercially available tests, the indirect fluorescent antibody test (IFAT) and the surface antigen 2, 4/3 ELISA (SAG2, 4/3 ELISA), using archived paired serum and CSF samples.Animals: Samples were obtained from 4 types of clinical patients. Confirmed positive cases (n = 9 horses; 11 sample sets) had neurologic deficits and postmortem lesions consistent with EPM. Confirmed negative cases (n = 28) had variable clinical signs and postmortem lesions consistent with another disease. Suspected positive cases (n = 6) had neurologic deficits consistent with EPM, marked improvement after treatment, and exclusion of other diseases. Suspected negative cases (n = 14) had variable signs with a strong presumptive diagnosis of another disease.Methods: For each test, descriptive statistics were calculated using serum results alone, CSF results alone, and a serum : CSF titer ratio.Results: Overall accuracy was highest for SAG2, 4/3 ELISA titer ratio at 0.97 (95% CI 0.88-0.99) with sensitivity = 0.88 (95% CI 0.66-0.97) and specificity = 1 (95% CI 0.92-1). IFAT CSF and titer ratio results also showed high accuracy at 0.88 (95% CI 0.77-0.94), but lower sensitivity = 0.65 (95% CI 0.41-0.83).Conclusions and Clinical Importance: Using serum results alone was least accurate for both test types. The more accurate methods, such as the SAG2, 4/3 ELISA serum : CSF titer ratio, should be utilized.

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“…Specifically, propagation of parasite cultures is relatively time-consuming and expensive, and the use of whole-parasite preparations can increase the risk of false-positive results due to cross-reactivity with closely related pathogens, such as Sarcocystis fayeri (11,38). Additionally, the current assays are not very amenable to quantitation, and their results can be subject to interpretation (16,32). Given these shortcomings, a detailed and in-depth characterization of equine humoral responses to S. neurona infection is not feasible with the existing serologic tests.…”

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confidence: 99%

Enzyme-Linked Immunosorbent Assays for Detection of Equine Antibodies Specific toSarcocystis neuronaSurface Antigens

Hoane

Morrow

Saville

et al. 2005

Clin Vaccine Immunol

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Sarcocystis neurona is the primary causative agent of equine protozoal myeloencephalitis (EPM), a common neurologic disease of horses in the Americas. We have developed a set of enzyme-linked immunosorbent assays (ELISAs) based on the four major surface antigens of S. neurona (SnSAGs) to analyze the equine antibody response to S. neurona. The SnSAG ELISAs were optimized and standardized with a sample set of 36 equine sera that had been characterized by Western blotting against total S. neurona parasite antigen, the current gold standard for S. neurona serology. The recombinant SnSAG2 (rSnSAG2) ELISA showed the highest sensitivity and specificity at 95.5% and 92.9%, respectively. In contrast, only 68.2% sensitivity and 71.4% specificity were achieved with the rSnSAG1 ELISA, indicating that this antigen may not be a reliable serological marker for analyzing antibodies against S. neurona in horses. Importantly, the ELISA antigens did not show cross-reactivity with antisera to Sarcocystis fayeri or Neospora hughesi, two other equine parasites. The accuracy and reliability exhibited by the SnSAG ELISAs suggest that these assays will be valuable tools for examining the equine immune response against S. neurona infection, which may help in understanding the pathobiology of this accidental parasite-host interaction. Moreover, with modification and further investigation, the SnSAG ELISAs have potential for use as immunodiagnostic tests to aid in the identification of horses affected by EPM.Sarcocystis neurona is a coccidian parasite that can infect horses and occasionally cause the neurologic disease equine protozoal myeloencephalitis (EPM) (6, 9). Horses become infected with S. neurona by ingesting sporocyst-contaminated food and water sources (8, 15). Ultimately, S. neurona can invade the central nervous system of the infected horse, causing focal or multifocal inflammation and EPM. S. neurona infection in horses is assessed by the detection of antibodies against the parasite in either the serum or cerebrospinal fluid (CSF); however, not all horses that seroconvert to S. neurona will develop EPM (9, 27). The seroprevalence of S. neurona infection in horses in the United States ranges between 0 and 89.2%, depending upon geographic locale (1-3, 10, 34, 37, 39, 40). In contrast, the incidence of clinical EPM has been estimated at Ͻ1% (28). It is not well understood what factors are responsible for the dichotomy between inapparent infection and clinical disease, but this ambiguity creates a major hindrance to EPM diagnosis and disease control.Current technologies for detecting S. neurona antibodies in equine serum and CSF samples include Western blotting (17), a modified version of Western blotting (35), an S. neurona direct-agglutination test (SAT) (25), and an indirect fluorescent-antibody test (5). Each of these current serodiagnostic assays utilizes complete S. neurona merozoite preparations as the antigen source, which has several drawbacks. Specifically, propagation of parasite cultures is relatively time-consuming ...

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Clinical Diagnosis of Equine Protozoal Myeloencephalitis (EPM)*

Cited by 60 publications

References 6 publications

Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies againstSarcocystis NeuronaandNeospora Hughesi

Effects of Blood Contamination of Cerebrospinal Fluid on Results of Indirect Fluorescent Antibody Tests for Detection of Antibodies againstSarcocystis NeuronaandNeospora Hughesi

Indirect Fluorescent Antibody Test and Surface Antigen ELISAs for Antemortem Diagnosis of Equine Protozoal Myeloencephalitis

Enzyme-Linked Immunosorbent Assays for Detection of Equine Antibodies Specific toSarcocystis neuronaSurface Antigens

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