Equine Protozoal Myelopathy (EPM) Flashcards
What is the primary causative agent for EPM?
Sarcocystis neurona
less commonly: neospora hughesi
Sarcocystis neurona has a 2-host life cycle. Who is the definitive host and who is/are the intermediate host(s)?
definitive = VA opposum
intermediate hosts = armadillo, skunk, raccoon, cat, sea otter
T/F: horses are dead end hosts for sarcocystis neurona
true – they obtain the organism by ingesting feed and water that is contaminated with possum poop (contains sporocytes)
This disease CANNOT be passed from horse-to-horse.
In which host does sarcosystis neurona form sarcocysts in?
the intermediate hosts.
Sarcocysts are found in the skeletal muscle, so for possums to get infected with this organism, they must consume the muscle of the intermediate hosts.
Why is testing for EPM not a reliable way to know the true # of horses that have developed disease from sarcocystis neurona?
There is a high prevalence of exposure (40-60% are +)
There is a low prevalence of clinical disease (<1%)
This means that the positive predictive value is LOW and the negative predictive value is HIGH.
what are factors that play a role in the <1% of horses that actually develop disease from sarcocystis neurona?
- stress
- season
- location
- age
- presence of other diseases (Ex. pregnant, PPID, etc.)
Clinical signs associated with EPM can vary and depend on the specific part of the CNS that is affected.
What are the 3 MOST common clinical signs of EPM?
- Ataxia
- Asymmetry
- Atrophy
these are slowly progressive most commonly, but they can be acute and severe.
T/F: EPM should be your top differential for multifocal CNS disease
true
When diagnosing EPM, its important to confirm the presence of clinical signs that are consistent with EPM by performing a complete neuro exam. You also need to rule out other diseases that could cause similar clinical signs. How can you do this?(5 diagnostic ways)
- lameness exam
- CBC/Chem (should be norm if EPM)
- Serology
- Radiographs/ myelogram
- CSF cytology (should be norm if EPM)
What should a CBC/Chem show in a horse with EPM?
Should be normal
What would the results of CSF cytology be in horses with EPM?
normal… but a abnormal CSF cytology does NOT rule out EPM.
What is the purpose of immunodiagnostic testing (ELISAs and IFAT) on serum and CSF in diagnosing EPM?
confirms intrathecal antibody production which rules out simple exposure.
What are two potential reasons for getting a positive CSF test for EPM in a horse that has positive serum titers but no clinical disease?
- passive transfer of antibodies across the blood brain barrier
- blood contamination of CSF during tap
Testing the blood for antibodies only tells us that a horse has been exposed to S. neurona. And, if we test the CSF, we cant be certain that antibodies are present due to intrathecal production or passive diffusion. What test can we do to reflect true intrathecal production of antibodies and can MOST reliably diagnose EPM premortem?
A ratio of serum antibody titer to the CSF antibody titer (SAG 2,4/3 ELISA)
If the CSF antibodies are as high of a concentration as the serum antibodies, they cannot be there from passive diffusion.
why is the SAG 2,4/3 ELISA considered a better test than the SAG 1 ELISA?
not all pathogenic S. neurona isolates express the SAG 1 antigen so there is a low sensitivity
SAG 2, 4/3 ELISA has shown to be the most consistently expressed antigens across s. neurona isolates.
