Infectious Diseases of the Nervous System Flashcards
What is the most frequent etiology of equine protozoal myeloencephalitis? What other microorganism can cause it? Where is this disease most common?
Sarcocystic neurona - obligate intracellular Apicomplexa
Neospora hughesi
USA —> NA opossums!
What are environmental/management, horse, and parasite risk factors that increase likelihood of EPM development?
stress, season, housing, food, region
use/breed, age, number, immunity
type, number
What is the lifecycle of Sarcocystis neurona like?
3 hosts
- DH - opossum
- IH - raccoons, house, armadillos, skunks
- aberrant hosts - horse ingestion of contaminated food or water with opossum feces
What is the suspected Neospora hughesi lifecycle?
indirect (2 hosts)
- DH - carnivores (dogs?)
- IH - ungulates (horses?) due to ingestion of contaminated food/water
What is the pathogenesis of EPM?
- inflammation
- neuronal necrosis
- lack of clearance from CNS
What 2 macroscopic lesions are seen with EPM? Where is this most commonly found?
- multifocal hemorrhage
- foci of malacia and discoloration
gray and white matter of the spinal cord and brainstem
What 3 microscopic lesions are seen with EPM?
- parasite observed
- diffuse nonsuppurative inflammation and necrosis
- perivascular infiltration of mononuclear cells
What are the most common signs seen with EPM?
STALL —> the great imposter
- stumbling or tripping
- tilted head
- asymmetrical muscle loss
- lameness
- leaning against walls
(AAA —> ataxia, asymmetry, atrophy)
What is the best antemortem diagnostic for EPM? What allows for definitive diagnosis?
positive serum/CSF ratio (intrathecal Ab) - many will be seropositive due to exposure, a negative is a good rule out
post-mortem examination (micro and macroscopic)
What are the 3 FDA-approved EPM treatments?
- Sulfonamide/Pyrimethamine
- Ponazuril (triazine antiprotozoal)
- Diclazuril (triazine antiprotozoal)
What form is Sulfadiazine/Pyrimethamine available in? What is its mechanism of action?
oral suspension - ReBalance
inhibits tetrahydrofolate synthesis
What is the duration of treatment of EPM with Sulfadiazine/Pyrimethamine? How is it offered with the diet?
90-270 days
withhold hay 2 hours before and after
What 3 adverse reactions are associated with Sulfadiazine/Pyrimethamine?
- anorexia
- intestinal issues
- bone marrow suppression
What formulation of Ponazuril is available? What is its mechanism of action?
oral paste - Marquis
acts on chloroplast-related material
What is the dose of Ponazuril like? What is the duration of treatment?
loading dose 3x normal dose for a day followed by normal maintenance dose
28 days or until no further improvement - will likely need 4-5 tubes
What formulation of Diclazuril? What is its mechanism of action? What is the duration of treatment?
pellets - Protazil
acts on chloroplast-related material
28 days, no loading dose needed (1 bucket)
What are some unofficial/off-label (illegal) drugs used for EPM?
- compounded Sulfadiazine/Pyrimethamine
- Diclazuril sodium salt/IV
- Toltrazuril (compounded with pyrimethamine) - Baycox, not approved in US
- Decoquinate + Levamisole - Orogin, not allowed in performance horses
Other than anti-protozoals, what are 3 other treatments used for EPM?
- anti-inflammatory - NSAIDs (Banamine), steroids if danger of recumbency
- anti-oxidants - DMSO, vitamin E
- supportive care - nutrition, preventative care
What is the prognosis of EPM like?
60% improve
- 10% relapse in 1-3 years
What are 2 important factors used to prevent EPM?
- avoid stress
- reduce exposure to opossum feces - feed off ground, separate fresh water source, no wildlife access to pasture or stalls
What are the 2 families of equine herpes virusus?
ALPHA
- EHV1: respiratory, abortion, neurologic
- EHV3: equine coital exanthema
- EHV4: upper respiratory (+ abortion)
GAMMA
- EHV2 an EHV5
What is the etiology of neurologic equine herpesvirus infection?
EHV1 (dsDNA)
- worldwide 80-100% of horses are infected and become carriers within their trigeminal ganglia
- OUTBREAKS
What are the 5 risk factors that increase the likelihood of developing neurologic herpesvirus infections?
- shedding horses kept close to susceptible horses
- stress
- season
- crowding, mingling with shared air space
- adult horses of tall breeds have a higher predisposition
What are the 2 forms of transmission of EHV1? What is its incubation period?
- DIRECT - respiratory (commonly before clinical signs), aborted materials
- INDIRECT - tack, equipment, people
4-7 days
What are the 3 phases to the pathogenesis of EHV1 infection?
- attachment and invasion of the respiratory epithelium, local LNs, and peripheral blood mononuclear cells
- PBMC association and viremia
- infection of endothelial cells, vasculitis, hemorrhage, thrombosis, and ischemia
What is the most consistent clinical sign associated with EHV1 infection?
biphasic fever
What acute signs are commonly associated with neurologic EHV1?
ascending ataxia and paresis
- posterior/anterior ataxia
- recumbency
What cauda equina signs are associated with neurologic EHV1?
- urinary and fecal incontinence
- loss of anal tone
- loss of sensation to perineum
What are 2 rarer presentations of neurologic EHV1? How do patients typically progress?
- facial nerve paralysis - drooping!
- depression
typically stabilizs in 24-48 hr
What samples are preferred for diagnosing EHV1?
- nasal swab with viral transport medium
- EDTA blood (within WBCs in buffy coat)
maximizes viral isolation
What is the quickest diagnostic for EHV1? What are some additional diagnostics available?
PCR - gB-based test or D752/N752 markers (allows for missing new strains)
- CSF: xanthochromia - high protein and normal cells
- seroconversion
- viral isolation
What treatment is recommended in horses with EHV1?
isolation, quarantine, supportive care - antivirals are expensive!
- keep standing, sternal with props, reposition recumbent
- easy access to food and water
- protect from trauma
- hydration
- evacuation of bladder and rectum
- keep handlers safe - neurologic horses are DANGEROUS
What 6 non-specific treatments can be used for horses with EHV1?
- NSAIDs: Firocoxib, Banamine - every day of fever and continued 3-5 days past
- steroids: Dexamethasone SPP
- antioxidants: vitamin E, DMSO
- antimicrobials for secondary infections: TMS, Ceftiofur
- virustatics ($$): valacyclovir, ganciclovir
- CRI Detomidine in thrashing horses
What is prognosis of EHV1 like?
standing = good
recumbent > 24 hrs = reserved
What are the 5 steps fo EHV1 outbreak management?
- quarantine of premise
- biosecurity - PPE, barriers
- confirm diagnosis with PCR in febrile and EHM horses, complete post-mortem exams, freeze serum
- monitor rectal temperatures 2x a day
- release premise in 21-28 days
How is EHV1 infection prevented? What is not available?
- biosecurity
- monitoring
- management
EHV1 vaccines do NOT protect against EHM
EHV vs. EHM:
What are the 5 AAEP core vaccines?
- West Nile
- Rabies
- Tetanus
- Eastern Equine Encephalomyelitis
- Western Equine Encephalomyelitis
(4 are viruses!)
