equine protozoal myeloencephalitis Flashcards
What are the causative organisms of equine protozoal myelitis?
Sarcocystis neurona
Neospora hughesiWhat
What is the definitive host of Sarcocystis neurona?
opossum Didelphis virginiana
What life stage of Sarcocystis neurona is passed in opposum feces?
sporozoite containing sporocysts
What stage of Sarcocystis neurona is infectious for the intermediate hosts?
sporozoites
What are intermediate hosts of S. neurona?
skunks
raccoons
armadillos
cats
What is the definitive host for Neospora caninum?
Canids
What is the seroprevalence of S. neurona in hroses from teh United states?
15 to 85%, dep on geographic location
In what season is S. neurona risk at the greatest?
-3x higher in spring and summer
-6 times higher in the fall
What are factors that increase the risk of horses contracting S. neurona?
-presence of opossums (2.5 fold)
-previous diagnosis of EPM (2.5 fold)
-presence of a wooded area (2 fold)
-stressful events, such as heavy exercise, transport, injury, surgery or parturition
-racehorses & show horses
Horses with EPM, that were treated with an anticoccidial drug were how many times more likely to improve than untreated horses?
10 times more likely to improve
What are presenting clinical signs of EPM?
-focal or multifocal signs of neurologic dz involving brain, brainstem or spinal cord
-C/S stabilize, only relapse days or weeks
-infection of both white & gray matter at multiple sites in CNS
What C/S are seen on neurologic examination?
asymmetric ataxia
weakness
spasticity involving on all 4 limbs
areas of hyporeflexia, hypalgesia or complete sensory loss
–>obtudnation, head tilt, facial nerve paralysis & difficulty swallowing
For highest accuracy in antemortem diagnosis of EPM, what is recommended?
- presence of C/S consistent with EPM on neurologic exam
- other potential causes are ruled out using available tools (ie cervical rads)
- Immunodaignostic testing of serum & CSF should be conducted to confirm intrathecal antibody production against S. neurona or N. hughesi
What is the recommended test for the EPM?
SnSAG2, 4/3 ELISA serum CSF titer ratio & NhSAG1 ELISA serum: CSF titer ratio
What are the most consistent/classical clinical signs of EPM?
assymetric gait & focal muscle atrophy
What are differentials for neurologic disease to rule out EPM?
-cervical stenotic myelopathy (CVSM)
-trauma
-EHV-1 associated neurologic disease
-equine motor neuron disease (EMND)
others: extradural & spinal cord tumors, epidural abscess, migrating metazoan parasites, rabies, WNV, equine degenerative myeloencephalopathy/nueroaxonal dystrophy, lead poisoning, creeping indigo toxicity, lymes diseas, etc
Confirmation of EPM on postmorten examination is based on what?
demonstration of protozoa in CNS lesions
What diagnostic tests exist for S. neurona & neospora EPM?
S. neurona:
-Western blot
-indirect flourescent antibody test (IFAT)
-surface antigen (SAG)
-enzyme-linked immunosorbent assays (ELISA)
Neospora:
-ELISA (NhSAG1)
-IFAT
What are the current FDA approved drugs?
-Ponazuril
-Diclazuril
-Sulfadiazine/Pyrmethamine
What is the mechanism of action of sulfonamides & pyrimethamine
act synergistically by interfering with folic acid metabolism & biosynthesis of purine & pyrimidine nucleotides necessary for parasites survival
What are the toxic effects of sulfadiaizne/pyrimethamine (REBALANCE)?
–related to inhibition of folate synthesis & include bone marrow suppression, anorexia, urticaria & self-limiting diarrhea
–progressive mild anemia
What will increase the bioavailability of FDA-approved ponazuril?
-concurrent administration of vegetable oil (1/2 cup)
What are other supportive medical treatments for EPM?
-NSAIDs- flunixin meglumine: 3-7 days of antiprotozoal treatment to prevent worsening neurologic signs
-corticosteroids: 0.1 mg/kg dex 1-2x daily
-DMSO: 1 g/kg as a 10% solution IV or via NGT
-Vitamin E: 20 IU/kg q24h
What is the best prevention of EPM?
-decreasing stress along with reducing exposure to scat from oppossums
