10 Equine Degenerative Myelopathy

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Questions and Answers

What is the primary role of Vitamin E in preventing Equine Degenerative Myelopathy (EDM)?

  • Boosting the immune response to central nervous system antigens.
  • Enhancing the structural integrity of neurons.
  • Promoting the synthesis of myelin sheath around nerve fibers.
  • Preventing oxidation of membrane lipids within the central nervous system. (correct)

Which of the following best describes the characteristic clinical presentation of Equine Protozoal Myeloencephalitis (EPM)?

  • Rapidly progressive muscle atrophy with hypersensitivity to touch.
  • Gradual onset of asymmetric neurological deficits. (correct)
  • Sudden collapse followed by generalized seizures.
  • Acute onset of symmetrical ataxia affecting all four limbs equally.

What is the significance of the N752/D752 mutation in the context of Equine Herpes Myeloencephalitis (EHM)?

  • It is a marker for increased shedding of the virus, leading to higher transmission rates.
  • It is associated with the neuropathogenic strains of EHV-1 due to a mutation at position 752. (correct)
  • It shows an increased likelihood of abortion in pregnant mares infected with the virus.
  • It indicates a stronger immune response, mitigating the severity of neurological signs.

Which diagnostic approach offers the most accurate assessment of disease likelihood in cases of Equine Protozoal Myeloencephalitis (EPM)?

<p>Cerebrospinal fluid analysis (w/out blood contamination) to characterize disease. (C)</p>
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What is the most critical factor to consider when collecting cerebrospinal fluid (CSF) for diagnosing Equine Protozoal Myeloencephalitis (EPM)?

<p>Ensuring minimal blood contamination to accurately measure antibody levels. (D)</p>
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A horse presents with clinical signs suggestive of Equine Degenerative Myelopathy (EDM). Serum vitamin E levels are marginal. What additional information would be most useful in supporting a diagnosis of EDM?

<p>Presence of symmetric ataxia and paresis that are worse in the pelvic limbs. (B)</p>
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Which statement accurately articulates the current understanding of the role of vaccines in managing Equine Herpes Myeloencephalitis (EHM)?

<p>Vaccination is not labeled for prevention of the neurologic disease, but may reduce shedding. (C)</p>
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What is the primary reason for the guarded prognosis associated with Equine Degenerative Myelopathy (EDM), even with early and consistent treatment?

<p>The irreversible nature of axonal necrosis and demyelination in the spinal cord. (A)</p>
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What is the primary rationale behind administering nonsteroidal anti-inflammatory drugs (NSAIDs) in the early stages of managing Equine Herpes Myeloencephalitis (EHM)?

<p>To reduce inflammation and control fever. (D)</p>
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Which key element in the life cycle of Sarcocystis neurona is most critical to target when implementing preventative measures against Equine Protozoal Myeloencephalitis (EPM)?

<p>Preventing the definitive host (opossum) from contaminating horse feed and water sources. (A)</p>
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What is the primary mechanism of action of ponazuril and diclazuril, the FDA-approved medications for treating Equine Protozoal Myeloencephalitis (EPM)?

<p>They target the parasite's apicoplast organelle, disrupting essential metabolic processes. (D)</p>
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In cases of Equine Herpes Myeloencephalitis (EHM), what is the significance of xanthochromia upon cerebrospinal fluid (CSF) analysis?

<p>It indicates previous hemorrhage, suggesting disruption of the blood-brain barrier. (D)</p>
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A horse is suspected of having Equine Degenerative Myelopathy (EDM) based on clinical signs. If postmortem necropsy is performed; where would be the most important region to examine for characteristic lesions?

<p>Brainstem and cervical and thoracic spinal cord. (B)</p>
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A horse displays asymmetric ataxia and muscle atrophy. If Equine Protozoal Myeloencephalitis (EPM) is suspected; where should you collect CSF to increase test sentitivity?

<p>Collect CSF from the site closest to the lesion. (C)</p>
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When assessing a horse with suspected Equine Herpes Myeloencephalitis (EHM) during an outbreak, what is the most appropriate protocol regarding isolation?

<p>Isolate for 21-28 days after resolution of signs or until a PCR test of a nasal swab returns a negative result. (C)</p>
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A horse is diagnosed with Equine Protozoal Myeloencephalitis (EPM) and treated with an FDA-approved medication. Despite initial improvement, the horse relapses several months later. What is the most important consideration for managing the relapse?

<p>Initiate a more aggressive treatment protocol, as the response to therapy is worse than the first episode. (B)</p>
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Which of the following is the most critical component in designing a biosecurity protocol to prevent the spread of Equine Herpes Myeloencephalitis (EHM) in a large boarding facility?

<p>Comprehensive vaccination program, combined with strict isolation protocols and hygiene practices. (A)</p>
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In the context of managing Equine Degenerative Myelopathy (EDM), what is the primary goal of advising Vitamin E supplementation in predisposed individuals?

<p>To prevent oxidation of CNS membrane lipids. (D)</p>
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What is the implication of a negative test for Sarcocystis neurona in a horse displaying clinical signs of neurological disease?

<p>It does not necessarily rule out EPM, as the disease could be caused by <em>Neospora hughesi</em>. (B)</p>
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What is the rationale for using valacyclovir in the treatment of Equine Herpes Myeloencephalitis (EHM)?

<p>To directly inhibit viral replication. (A)</p>
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What is the best description of the typical signalment of horses that develop Equine Degenerative Myelopathy (EDM)?

<p>Foals and young horses (typically less than one year old) of specific predisposed breeds. (A)</p>
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Which of the following clinical signs is most suggestive of Equine Herpes Myeloencephalitis (EHM) rather than Equine Protozoal Myeloencephalitis (EPM)?

<p>Symmetric ataxia and weakness, particularly with hindlimb involvement and poor tail tone. (A)</p>
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What characteristic finding on CSF analysis is most suggestive of Equine Herpes Myeloencephalitis (EHM)?

<p>Xanthochromia with Albuminocytologic dissociation. (C)</p>
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What statement best summarizes the approach to managing Equine Protozoal Myeloencephalitis (EPM) to minimize the risk of relapse after successful treatment?

<p>Preventative maintenance therapy. (C)</p>
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How could Equine Protozoal Myeloencephalitis be prevented?

<p>Protected feed and grain products. (D)</p>
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When does relapse occur for Equine Protozoal Myeloencephalitis (EPM)?

<p>Months to years after discontinuation of treatment. (A)</p>
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Which of the following is not a clinical sign of Equine Herpes Myelitis (EHM)?

<p>Hypermetria. (C)</p>
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The gene sequence determines pathogenicity for Equine Herpes Virus. Which has a high virulance in order?

<p>Ab4. (A)</p>
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Which of the following has FDA approval for Equine Protozoal Myeloencephalitis (EPM) treatment?

<p>ReBalance Pharmical. (D)</p>
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Which of the following is not a cause of Equine spinal ataxia?

<p>Equine influenza. (C)</p>
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Which of the following breeds are not predisposed to Equine Degenerative Myelopathy (EDM)?

<p>Thoroughbred. (A)</p>
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How often should a horse be treated with Propionibacterium acnes if following label instructions?

<p>Three times in one week. (A)</p>
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What lesion region would be associated with Equine Protozoal Myeloencephalitis?

<p>Spinal cord mostly, or corticol and brainstem. (D)</p>
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What is the relationship between Equine Herpesvirus-1 respiratory infection and Equine Herpes Myeloencephalitis (EHМ)?

<p>Access the risk and prognosis associated with EHM, particularly in large groups of performance horses. (B)</p>
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At what vitamin E µg/mL level is a horse considered normal and adequate to support neurologic and muscular function?

<blockquote> <p>4 µg/mL. (B)</p> </blockquote>
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What serum:CSF ratio result would indicate a postive EPM test?

<p>Serum:CSF &lt; 100. (A)</p>
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What is the primary neuropathological finding that differentiates Equine Degenerative Myelopathy (EDM) from Neuroaxonal Dystrophy (NAD)?

<p>Axonal necrosis and demyelination predominantly in the dorsal and ventral spinocerebellar tracts of the cervicothoracic spinal cord. (C)</p>
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Considering the complex interplay of factors contributing to Equine Degenerative Myelopathy (EDM), which of the following best describes its etiology?

<p>A multifactorial condition involving genetic susceptibility, Vitamin E deficiency, and oxidative stress. (D)</p>
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A veterinary practice is located in a region with a known high seroprevalence of Sarcocystis neurona. Which of the following strategies would be most effective in reducing the incidence of new Equine Protozoal Myeloencephalitis (EPM) cases?

<p>Implementing measures to reduce opossum access to horse feed and pasture areas, coupled with strategic surveillance. (C)</p>
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A horse exhibits asymmetric ataxia, hindlimb weakness, and focal muscle atrophy. Diagnostic testing confirms Equine Protozoal Myeloencephalitis (EPM). Despite treatment with an FDA-approved medication, the horse shows only marginal improvement. What is the most appropriate next step?

<p>Re-evaluate the diagnosis, consider other differentials, and adjust the treatment plan based on new findings. (A)</p>
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In a large equine practice, a cluster of horses suddenly develop neurological signs, including fever, ataxia, and urinary incontinence. Equine Herpes Myeloencephalitis (EHM) is suspected. What immediate action should be taken to control the outbreak and minimize further spread?

<p>Implement strict biosecurity protocols, isolate affected horses, and monitor all horses for fever and neurological signs. (B)</p>
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Following a confirmed outbreak of Equine Herpes Myeloencephalitis (EHM) in a boarding facility, what is the most critical long-term biosecurity measure to implement to prevent future outbreaks?

<p>Requiring all new horses entering the facility to have a negative EHV-1 PCR nasal swab, regardless of vaccination status. (D)</p>
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A young horse presents with symmetrical ataxia and paresis, worse in the hind limbs. Serum vitamin E levels are within the marginal range. To further investigate a possible diagnosis of Equine Degenerative Myelopathy (EDM), what additional diagnostic step would be most informative?

<p>Evaluate the horse's diet and management practices, coupled with a trial supplementation of natural vitamin E, followed by reassessment of neurological signs. (D)</p>
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Considering the limitations of antemortem diagnostics for Equine Degenerative Myelopathy (EDM), which combination of clinical findings and diagnostic results would most strongly suggest EDM?

<p>Symmetrical ataxia in a young horse (less than 1 year old) with marginal to low serum vitamin E, normal CSF analysis, and exclusion of other neurological diseases. (C)</p>
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A horse diagnosed with Equine Protozoal Myeloencephalitis (EPM) initially responds well to treatment but relapses several months later with similar neurological deficits. What factor is most likely contributing to the relapse?

<p>Re-exposure to <em>Sarcocystis neurona</em> coupled with incomplete initial eradication of the parasite from the central nervous system. (C)</p>
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What is the most accurate statement regarding the impact of vaccination on Equine Herpes Myeloencephalitis (EHM) outbreaks?

<p>Vaccination may reduce viral shedding and disease severity; however, it does not fully prevent infection or eliminate the risk of EHM. (C)</p>
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Based on current understanding of Equine Degenerative Myelopathy (EDM), which of the following management strategies is most likely to improve long-term outcomes in affected horses?

<p>Early and consistent supplementation with natural vitamin E, alongside regular exercise and environmental management to reduce stress. (B)</p>
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A horse presents with acute onset of fever, severe ataxia, and urine dribbling. Cerebrospinal fluid (CSF) analysis reveals xanthochromia and elevated protein levels, with a normal cell count. Which of the following is the most likely diagnosis?

<p>Equine Herpes Myeloencephalitis (EHM). (B)</p>
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In comparing Equine Protozoal Myeloencephalitis (EPM) and Equine Herpes Myeloencephalitis (EHM), which statement best differentiates the typical clinical presentation of these diseases?

<p>EPM often involves cranial nerve deficits and muscle atrophy, whereas EHM is characterized by acute onset of fever and urinary incontinence. (D)</p>
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What is the significance of albuminocytologic dissociation in cerebrospinal fluid (CSF) analysis in cases of Equine Herpes Myeloencephalitis (EHM)?

<p>It indicates a breakdown of the blood-brain barrier, leading to increased protein concentration without a corresponding increase in cell count. (D)</p>
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Which factor is least likely to impact the efficacy of treatment for Equine Protozoal Myeloencephalitis (EPM)?

<p>Concomitant use of nonsteroidal anti-inflammatory drugs (NSAIDs). (A)</p>
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In a region with high Sarcocystis neurona seroprevalence, what result would give the highest confidence that a horse's neurological issues are due to EPM?

<p>A positive S. neurona antibody titer in serum and CSF with a serum:CSF ratio &lt; 100. (D)</p>
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Which of the following scenarios poses the highest risk for the development of Equine Herpes Myeloencephalitis (EHM) within a closed herd of horses?

<p>A new horse is introduced to the herd without a quarantine period or prior EHV-1 testing. (B)</p>
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What is the primary reason behind the recommendation to administer vegetable oil alongside ponazuril when treating Equine Protozoal Myeloencephalitis (EPM)?

<p>To enhance the absorption of ponazuril from the gastrointestinal tract. (A)</p>
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Which diagnostic result would be most indicative of EHV-1 as the causative agent in a horse displaying acute neurological signs?

<p>Detection of EHV-1 DNA in nasal secretions or cerebrospinal fluid (CSF) via quantitative PCR (qPCR). (C)</p>
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What is the most likely implication of a negative Western blot test for Sarcocystis neurona in a horse displaying neurological signs consistent with Equine Protozoal Myeloencephalitis (EPM)?

<p>The horse does not have EPM, and alternative diagnoses should be investigated. (A)</p>
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Which of the following statements most accurately describes the role of the opossum in the transmission of Equine Protozoal Myeloencephalitis (EPM)?

<p>Opossums are the definitive host of <em>Sarcocystis neurona</em>, shedding sporocysts in their feces that can then be ingested by horses. (B)</p>
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Considering the clinical presentations and diagnostic challenges, what is the most appropriate approach to differentiating between Equine Degenerative Myelopathy (EDM) and Cervical Vertebral Stenotic Myelopathy (CVSM) in a young horse?

<p>A thorough neurological exam, combined with assessment of serum vitamin E levels, cervical radiographs, and exclusion of other differentials, is necessary to differentiate between the two conditions. (B)</p>
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In the context of Equine Herpes Myeloencephalitis (EHM), what is the primary rationale for using valacyclovir?

<p>Valacyclovir is converted to acyclovir, which inhibits viral DNA replication. (C)</p>
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A horse with confirmed Equine Protozoal Myeloencephalitis (EPM) is being treated with ponazuril. What adjunctive therapy would provide NO benefit?

<p>Antimicrobials. (C)</p>
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Which statement accurately describes the role of genetic predisposition in Equine Degenerative Myelopathy (EDM)?

<p>Certain breeds and families of horses have a higher incidence of EDM, suggesting a complex heritable component that increases susceptibility. (B)</p>
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Which of the following best describes the diagnostic approach for Equine Degenerative Myelopathy (EDM)?

<p>Diagnosis of exclusion. (A)</p>
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During an Equine Herpes Myeloencephalitis (EHM) outbreak, which action poses the highest risk for spreading the virus?

<p>Allowing horses to have nose-to-nose contact with non-effected horses. (D)</p>
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When considering treatment options for a horse diagnosed with Equine Protozoal Myeloencephalitis, which additional immune modulating therapy would be least benificial if using traditionally effective approaches?

<p>Increasing Vitamin D intake. (D)</p>
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With regards to the EPM parasite Sarcocystis neurona, where is the most common lesion location?

<p>Spinal cord. (B)</p>
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Flashcards

Equine Degenerative Myelopathy (EDM)

A neurological disease in horses characterized by neuronal degeneration.

Spheroids

Degenerating neurons and axons that are swollen.

EDM location in spinal cord

Dorsal and ventral spinocerebellar tracts of cervicothoracic spinal cord.

EDM Pathogenesis

Genetically susceptible individuals deficient in vitamin E in the first year of life. Inadequate vitamin E causes oxidation of CNS membrane lipids.

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EDM Onset

Clinical signs usually begin in the first year of life.

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EDM Predisposed Breeds

Morgan, Appaloosa, and Lusitano horses.

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EDM Clinical Signs

Symmetric ataxia and paresis of trunk and limbs, worse in pelvic limbs. Often see wide-based stance and gait with spasticity.

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EDM Diagnosis

No confirmatory antemortem diagnostic test exists. Postmortem necropsy of brainstem and cervical/thoracic spinal cord is required.

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Treatment of EDM with Vitamin E

Important for uptake by the liver to supplement vitamin E.

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Key factors of EDM

Symmetric spinal ataxia in young horses, Vitamin E deficiency, breed predisposition.

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Equine Protozoal Myelitis (EPM)

Protozoal disease, life cycle involves the opossum as the definitive host.

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Intermediate hosts for EPM

Raccoon, armadillo, skunk and cat.

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EPM Signalment

All breeds have been reported. 62% of cases are in horses < 4 years of age

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EPM Prevalence

Seroprevalence lower in the western states and far northeast. Higher in southeastern central states due to opossums.

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EPM Season of Development

Spring and Summer.

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EPM Neurologic Signs

Asymmetric neurologic presentation.

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Location of EPM lesions

Spinal cord (85%) and Cortical and brainstem (15%).

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CSF Collection for EPM

Collection of CSF to obtain a sample as close to lesion.

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EPM Diagnosis

Commercial testing for antiprotozoal antibodies, particularly Sarcocystis neurona and Neospora hughesi.

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Serology for EPM

Determines exposure only.

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Normal CSF Cytology

CSF should be clear and colorless. Normal cell count less than 5-8 / uL

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Surface antigen ELISA for EPM

Accurately detects S. neurona antibodies in serum and CSF.

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EPM Treatment

Benzeneacetonitrile (triazine) medications.

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Ponazuril Use

Benzeneacetonitrile: 15 mg/kg PO loading, then 5 mg/kg PO daily x 28d. Administer with vegetable oil to enhance absorption.

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ReBalance

Combination of pyrimethamine and sulfadiazine (PYR/SDZ).

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EPM Treatment Efficacy

62-67% response rate with FDA-approved compounds.

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Clinical Management of EPM

NSAID medications for the first 5-7 days of therapy. CCS used for cortical disease.

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EPM Prevention

Prevent contact with opossums and protect feed / grain products.

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Equine Herpes Myeloencephalitis (EHM)

A neurologic disease form of Equine Herpesvirus (EHV) infection.

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EHM Signalment

Aged (> 20 years) horses are more susceptible.

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Gene Sequence EHM

Determine pathogenicity of neuropathic EHV

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EHM Virulence

Ab4 determines high virulence.

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EHV-1 DNA ORF 30

Confirmation of EHV-1 aids in clinical management. Mutation is associated with neurologic disease.

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EHV-1 Paralysis vs Abortion

Paralysis Magnitude and duration is higher for parlytic strain

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EHM Clinical Signs

Symmetric weakness and ataxia. Ascending myelitis. Hind >>>> fore.

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EHM Specific Clinical Signs

Urine dribbling and prolapsed penis in stallions.

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EHM Diagnosis

Xanthochromia and and elevated levels of total protein (>150 mg/dl).

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EHM Treatment

Supportive care with a sling, good footing, and urinary catheter.

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EHM Drug Treatment

NSAIDs, CCS drugs and Valacyclovir(antiviral therapy).

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EHM Carriers

Viral latency induced by herpes viruses.

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EHM Prevention

Current vaccine not labeled for neurologic disease.

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Study Notes

Equine Degenerative Myelopathy (EDM)

  • EDM involves neuronal degeneration
  • EDM is on a continuum of Neuroaxonal Dystrophy (NAD)
  • Dystrophic neurons and axons have spheroids, which are swollen axons
  • In NAD, brainstem nuclei are affected
  • In EDM, the dorsal and ventral spinocerebellar tracts of the cervicothoracic spinal cord are affected
  • EDM causes axonal necrosis and demyelination
  • The exact cause and underlying mechanisms are unknown
  • EDM occurs in genetically predisposed individuals with vitamin E deficiency within their first year
  • Vitamin E deficiency is associated with oxidation of central nervous system membrane lipids
  • Clinical signs typically begin in the first year
  • Morgan, Appaloosa, and Lusitano breeds are more prone to EDM
  • Standardbred, Paso Finos, Norwegian Fjord, Arabian, Welsh pony, Haflinger, and Quarter Horse breeds may also be affected
  • Symmetric ataxia and paresis occur in the trunk and limbs
  • EDM is worse in the pelvic limbs
  • Affected horses exhibit a wide-based stance and gait, spasticity, and a 2-beat lateral "pacing" walk
  • Long spinal reflexes are reduced or absent and the cutaneous trunci is affected
  • It is localized in the spinal cord, specifically in the cervical vertebrae; may also be diffuse
  • No specific antemortem test exists
  • it is diagnosed through exclusion of other conditions
  • Cerebrospinal fluid (CSF) analysis, cervical vertebral radiographs, and myelogram are normal
  • Postmortem necropsy reveals lesions in the brainstem, cervical, and thoracic spinal cord
  • A serum vitamin E level of >4 µg/mL (or >400 µg/dL) is considered normal for supporting neurological and muscular function
  • A serum vitamin E level of 2-4 µg/mL (200-400 µg/dL) indicates marginal/borderline status and a risk of deficiency if persistent or combined with stressors
  • A serum vitamin E level of <2 µg/mL (or <200 µg/dL) indicates vitamin E deficiency and an increased risk for neurologic conditions like EDM
  • Vitamin E supplementation is used as treatment.
  • Natural Vitamin E is needed for uptake by the liver
  • Administer 10-20 IU/kg PO daily (5,000-10,000 IU)
  • Monitor serum vitamin E levels.
  • Prognosis for recovery is guarded, even with early treatment
  • Vitamin E supplementation may serve as preventative for predisposed horses

Equine Protozoal Myelitis (EPM)

  • The term was created in the mid 1970's
  • The causative agent Sarcocystis neurona was cultured from an affected horse's spinal cord in 1991
  • Its life cycle involves the opossum as the definitive host
  • Intermediate hosts include raccoons, armadillos, skunks and cats
  • The related protozoa Neospora hughesi can also cause EPM-like signs
  • All breeds have been reported
  • 62% of cases are in horses under 4 years of age
  • 20% cases are in horses over 8 years of age
  • Peak incidence occurs from 15 months to 5 years
  • Standardbreds, Thoroughbreds, and Quarter Horses are common breeds
  • Overall seroprevalence from US submissions is around 60%
  • Seroprevalence ranges from 31-85% in Arizona/Arkansas
  • Seroprevalence is lower in the western and far northeast states, and higher in the southeastern central states
  • States with moderate seroprevalence (22-42%) may test negative for EPM
  • States with higher seroprevalence may still have up to 20% test negative cases.
  • The western blot is a useful tool
  • A negative test helps rule out S. neurona caused EPM
  • EPM has a predilection in the fall and spring/summer
  • It presents with spinal cord lesions in 85% of cases, cortical and brainstem lesions in 15%
  • Multifocal and asymmetric signs are highly suspect for EPM
  • Focal muscle atrophy occurs
  • Disease progression may be insidious and progressive, acute, or static
  • Serology only determines exposure
  • It can help refine the differential diagnosis.
  • CSF analysis is more accurate for disease likelihood
  • collect CSF samples as close to lesion as possible at the AO, C1-2, and LS locations
  • Increasing test sensitivity is gained via an increased concentration of antibodies
  • Normal CSF cytology shows clear, colorless fluid
  • A cell count of <5-8/uL
  • Protein concentration of <50-80 mg/dL
  • Glucose at 80% of circulating levels
  • Commercial testing exists for antiprotozoal antibodies of S. neurona and N. hughesi
  • Testing can be performed on serum, CSF, or both
  • Western blot is qualitative and examines antibodies against merozoite lysate
  • Indirect fluorescent antibody test is quantitative and examines antibodies against culture-grown merozoites. The titer is a poor predictor and has low specificity
  • Surface antigen ELISAs detect SnSAG 2 and SnSAG 4/3 antibodies in serum and CSF
  • A serum to CSF ratio provides the highest diagnostic accuracy
  • A serum:CSF <100 indicates a positive test for EPM
  • FDA approved treatments: Benzeneacetonitrile (triazine) medications
  • They target the parasite's apicoplast organelle
  • Can use Ponazuril at 15 mg/kg PO loading, then 5 mg/kg PO daily x 28 days
  • Ponazuril should be administered with vegetable oil to enhance absorption
  • Diclazuril can be used with no loading dose: label 1 mg/kg PO daily x 28 days
  • ReBalance® is FDA approved, includes pyrimethamine and sulfadiazine, and blocks protozoal folate synthesis
  • Administer by PYR 1 mg/kg PO daily and SDZ 20 mg/kg PO daily on an empty stomach
  • FDA-approved compounds have a 62-67% response rate
  • Treatments improve at least 1 grade or result in negative antibody tests in serum and CSF
  • Triazines have minimal toxicity, while pyrimethamine is not recommended in broodmares
  • Treat for 6-8 weeks minimum
  • NSAIDs may be used for the first 5-7 days of therapy: Flunixin meglumine 0.5-1.1 mg/kg IV/PO and Phenylbutazone 2.2-4.4 mg/kg IV/PO
  • Corticosteroids can be employed for rapidly progressive, recumbent or cortical manifestations
  • Antioxidant therapy with DMSO: 0.5-1 g/kg/day for 3-6 days alongside Vitamin E at 1000-10,000 IU can be beneficial
  • Immunostimulant therapy with Propionibacterium and Levamisole can be used
  • Demonstrate improvement – 60-70%
  • One grade improvement occurs with medications
  • 10-20% complete recovery can occur
  • Neurologically normal return occurs less than 20%
  • Recumbency and muscle mass loss are associated with a poor prognosis
  • Relapse occurs in 10% of cases
  • Deficits are similar to previous episodes
  • Symptoms can return months to years after discontinuation
  • Response to treatment is worse than the first episode
  • Relapses require more aggressive treatment and preventative maintenance therapy.
  • To prevent EPM, avoid contact with opossums and protect food/grain
  • FDA-approved drugs can be used strategically
  • Ponazuril can be used at 2.5-5.0 mg/kg PO daily before exposure or 20 mg/kg PO every 7 days.
  • Diclazuril at 0.5 mg/kg PO daily.

Equine Herpes Myelitis (EHM)

  • Equine Herpesvirus (EHV) causes rhinopneumonitis and can manifest in respiratory, abortion/perinatal, neurologic diseases, and chorioretinitis
  • EHV has caused the FEI to shutdown international events due to the EHV-1 outbreak; it is a common DNA virus
  • No gender, breed, geographic, or seasonal predilection
  • Aged (>20 years) horses are more susceptible
  • Fever presents 5 to 7 days prior to neurologic signs
  • Unique EHV-1 strains can remain abortogenic but show single AA substitution
  • Unique EHV-1 strains includes a DNA polymerase shift
  • Position 752: asparagine is replaced with aspartic acid
  • Gene sequence determines pathogenicity
  • Ab4 is high virulence and V592 is low virulence
  • Sequence variation at ORF30 for viral DNA polymerase is associated with paralytic viruses
  • Confirmation of EHV-1 aids in clinical management
  • Mutation is associated with neurologic disease; interpret with caution
  • 14-24% of EHV-1 isolates in horses with EHM do not have mutation
  • When infected with the neuropathic strain, the OR of neurologic disease is 162 x greater
  • EHV is evolving in virulence and behavior; USDA designation: Potentially Emerging
  • Clinical signs present with symmetric weakness and ataxia
  • Ascending myelitis occurs from Hind >>>> fore
  • Poor tail tone is a symptom
  • Urine dribbling and prolapsed penis are also symptoms

EHM CSF Analysis

  • Xanthochromia
  • Total protein > 150 mg/dl
  • Normal cell count (<5-8 cells/µL)
  • Albuminocytologic dissociation
  • High protein
  • Normal cell concentration
  • CSF titers - unreliable
  • A diagnosis of neuropathic EHV 1 involves a Quantitative PCR (qPCR)
  • This can be done on CSF, nasal secretions, pharyngeal swab, or buffy coat
  • Virus isolation
  • Treatment includes supportive care such as a sling, good footing and a urinary catheter
  • Anti-inflammatory drugs like NSAIDs (flunixin meglumine) are used at 0.5-1.1 mg/g PO / IV 5-10 days
  • As well as CCS (dexamethasone) at 0.05-0.1 mg/kg PO / IV 1-3 days
  • Valacyclovir is used at 30-40 mg/kg PO TID to BID x 7-10 days
  • A prognosis for recovery is good if standing
  • Once infected, patients are carriers for life due to latency
  • The best strategy to prevent is BIOSECURITY
  • High antigen EHV-1 vaccines are recommended, but currently no approved vaccine exists
  • Vaccination may reduce shedding
  • Isolate affected horses for 21-28 days after resolution of signs or until PCR of nasal swab is negative

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