Infectious Diseases of the Nervous System Flashcards by Renee DeAngelis

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!

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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

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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

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What is the suspected Neospora hughesi lifecycle?

indirect (2 hosts)

DH - carnivores (dogs?)
IH - ungulates (horses?) due to ingestion of contaminated food/water

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What is the pathogenesis of EPM?

inflammation
neuronal necrosis
lack of clearance from CNS

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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

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What 3 microscopic lesions are seen with EPM?

parasite observed
diffuse nonsuppurative inflammation and necrosis
perivascular infiltration of mononuclear cells

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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)

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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)

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What are the 3 FDA-approved EPM treatments?

Sulfonamide/Pyrimethamine
Ponazuril (triazine antiprotozoal)
Diclazuril (triazine antiprotozoal)

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What form is Sulfadiazine/Pyrimethamine available in? What is its mechanism of action?

oral suspension - ReBalance

inhibits tetrahydrofolate synthesis

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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

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What 3 adverse reactions are associated with Sulfadiazine/Pyrimethamine?

anorexia
intestinal issues
bone marrow suppression

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What formulation of Ponazuril is available? What is its mechanism of action?

oral paste - Marquis

acts on chloroplast-related material

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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

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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?

1. attachment and invasion of the respiratory epithelium, local LNs, and peripheral blood mononuclear cells 2. PBMC association and viremia 3. 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?

1. facial nerve paralysis - drooping! 2. 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?

1. NSAIDs: Firocoxib, Banamine - every day of fever and continued 3-5 days past 2. steroids: Dexamethasone SPP 3. antioxidants: vitamin E, DMSO 4. antimicrobials for secondary infections: TMS, Ceftiofur 5. virustatics ($$): valacyclovir, ganciclovir 6. 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?

1. quarantine of premise 2. biosecurity - PPE, barriers 3. confirm diagnosis with PCR in febrile and EHM horses, complete post-mortem exams, freeze serum 4. monitor rectal temperatures 2x a day 5. 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?

1. West Nile 2. Rabies 3. Tetanus 4. Eastern Equine Encephalomyelitis 5. Western Equine Encephalomyelitis (4 are viruses!)