Equine Infectious Neurology Flashcards
West Nile Virus - Background
» Vector borne Flavivirus
» Causes West Nile Encephalitis
» Zoonotic notifiable
* ‘Testing for Exclusion’ Scheme (APHA)
* Not in the UK, but likely to come – we have the vector (Culex pipiens) * Seen in horses travelling from endemic countries (2019, 2022)
* Important to know clinical signs and what to do if suspect a case
Report to DEFRA rural services hotline
* Europe,N.&S.America,Asia,Africa… » UK surveillance to monitor risk
West Nile Virus - Clinical Signs
- Dull/lethargic/somnolence
- Fever
- Facialparalysis,dysphagia
- Musclefasciculations
- Para or tetra-paresis
- Ataxia
- Recumbency
West Nile Virus - Diagnosis
- IgM capture ELISA, (Ab detection cELISA) on serum or CSF
- CSF analysis: Pleocytosis (lymphocytosis), elevated protein levels
- Postmortem: PCR from tissue sample
West Nile Virus - Prevention and Tx
» Treatment
* No specific treatment
* ICU nursing care and monitoring, NSAIDs, recumbent horse care
» Vaccination
* Inactivated vaccine
* May complicate testing
* Core vaccine in North America
* Risk basis in the UK (horses travelling to endemic countries)
Equine Herpesvirus Myeloencephalopathy
» Caused by EHV-1, which is (to some extent) endemic
1. Respiratory disease in young horses (weanlings, yearlings) Outbreaks in overcrowd, stressful environments
* Fever, cough, nasal discharge
* Older horses (subclinical infection) play important role in outbreaks
2. Abortion or neonatal death: ‘Abortion storm’
* Neonatal septicemia, death
3. Equine Herpesvirus myeloencephalopathy (EHM)+/-pyrexia, respiratory signs
* Can occur singly or results in an outbreak
Equine herpesvirus myeloencephalitis
Equine herpesvirus myeloencephalitis Signs
- Pyrexia, dull, inappetent – viraemic phase
- Sudden onset neurological signs
- Ataxia & paresis: hindlimbs > forelimbs
- Caudal spinal cord segments (Cauda equina signs)
- Bladder distension and urinary incontinence
- Faecal retention
- Penile protrusion in males
- Flaccid tail & anus
Equine Herpesvirus Myeloencephalitis Diagnosis
- Nasal or nasopharyngeal swab PCR
- Serology (paired serology)
- Virus isolation
- CSF: Xanthochromic (yellow)
CSF Analysis:
» Viral/bacterial encephalitis, meningitis, abscess, haemorrhage, neoplastic disease
» Atlanto-occipital (AO) tap: requires short anaesthesia but relatively straightforward technique
» Lumbosacral tap: Standing sedation
» Standing cervical centesis: Ultrasound guided centesis of C1-C2
EHM treatment
» Treatment:
* Symptomatic
* NSAIDs, nursing, palatable feed, IVFT
* Anti-viral medication
* Valacyclovir
* Biosecurity essential - Isolate
* Prognosis variable
* Better chance of full recovery if not recumbent
* If recumbent >24h: Grave prognosis
EHM Vaccination:
» At-risk basis
» Competition horses that are subject to periods of stress and gather with large #s of horses
» Not usually recommended in the face of an outbreak of EHM
Toxicoinfectious Diseases: Tetanus and botulism
» Clostridial neurotoxins inhibit neurotransmitter release
* Tetanus: tetanic/spastic paralysis
* Botulism: flaccid paralysis
Tetanus: Overview
» Clostridium tetani
* Gram positive, obligate anaerobe
* Spore forming bacteria
* Ubiquitous in soil/faeces
Forms three toxins: tetanospasmin and tetanolysin most important
* Antibodies to tetanospasmin are protective (vaccination)
» Infection with spores→‘tetanus’
* Wounds
* Especially if deep, necrotic/reduced blood supply
* Penetrating wound, injection site abscess, metritis, castration,
foot abscesses…
* Routine prophylaxis (vaccination) is important
* Cases may have no visible wounds
Tetanus Pathogenesis
Learn flowchart
Tetanus Clinical Signs
- Localized stiffness–muscles around original infection
- Jaw, (Lock jaw), Neck, hind limbs
- Third eyelid protrusion, nostril flaring, raised tailhead
- Progresses to generalised stiffness (saw-horse stance)
- Dysphagia
- Hyperaesthesia (spasms to touch and sound)
- Recumbency, paralysis or respiratory muscles
- Autonomic signs
- Tachy/brady dysrhythmias
- Miosis
Tetanus Treatment
- Eliminate C. tetani organism
- Penicillin or metronidazole
- Clean and debride wound
- Neutralise toxin
- Antitoxin: does not neutralise toxin that is
already in nerve
- Antitoxin: does not neutralise toxin that is
- Give antitoxin BEFORE wound debridement
- Give tetanus vaccine (toxoid) to stimulate
active immunity
» Control muscle spasm - Drugs like methocarbamol and diazepam can be used
- ACP (not hugely effective), alpha 2 agonists
» Nursing - Padded stable ideal
- Or anaesthetic induction box
- May need slinging
- Minimise stimulation
- Cotton wool in ears
- Low light
- Low traffic
- Nutritional support and hydration
- Sling if recumbent
Tetanus Prevention
» Tetanus toxoid
* Start at 6mo of age
» Two vaccines four weeks apart
* 1st booster 6-24 months (depends on product)
* Boosters usually every 2 years
» Vaccinate mares in last trimester to confer immunity via colostrum
» Tetanus antitoxin
» Used to provide protection during risk period
* Any unvaccinated horse with
wound/castration/abscess
* Combination of toxoid and antitoxin often
given to at-risk/naïve horses
* Often given to foals at 1 day old?
* Comes in big bottles, expensive…in theory
shouldn’t be used after broached for >24h!
Botulism Overview
» Rare in the UK
» USA higher prevalence
* Vaccination in high prevalence areas of USA (Kentucky)
» 8 different serotypes based on toxin produced (A to G)
* Geographic
* Affects treatment
» Route of entry
* 1. Ingestion of pre-formed toxin ‘forage poisoning’
* 2. Ingestion of spores, production of toxin in GIT,
* 3. C. Botulinum infection via wound
Botulism: Pathogenosis
LEARN FLOWCHART
Botulism Clinical signs
- Weakness, poor muscle tone, flaccidity
- Ptyalism, loss of tongue tone
- Cranial nerve dysfunction – dysphagia, ptosis
- Trembling, sweating, laboured breathing
- Reduced parasympathetic activity → decreased GIT motility
- Progress to recumbency
- Death may occur due to paralysis of respiratory muscles
Botulism Treatment
- Nursing: palatable soft feed
- Sling if needed
- Ventilator in young foals
- Supportive/symptomatic treatment
- Hyperimmune plasma
- Botulinum antitoxin – need to know the correct serotype
Botulism Diagnosis
- History spoiled feed
- Clinical signs
- Lab tests challenging/unreliable
Equine Grass sickness (equine dysautonomia) - Background
Grass sickness/equine dysautonomia
Risk factors
» 2-7yrs old
» Recent movement
» Recent anthelmintic administration » Particular pasture
» Disturbed pasture
» Mechanical poo picking
» Cool, dry weather and irregular frost
