Week 4- Equine Infectious Neurological Diseases Flashcards
What is West Nile Virus?
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…
What are the Clinical signs of West Nile Virus?
Dull/lethargic/somnolence
* Fever
* Facial paralysis, dysphagia
* Muscle fasciculations
* Para or tetra-paresis
* Ataxia
* Recumbency
How would you diagnose West Nile Virus?
IgM capture ELISA, (Ab detection cELISA) on serum or CSF
* CSF analysis: Pleocytosis (lymphocytosis), elevated protein levels
* Postmortem: PCR from tissue sample
How would you treat West Nile Virus?
No specific treatment
* ICU nursing care and monitoring, NSAIDs, recumbent horse care
How would you vaccinate against West Nile Virus?
Inactivated vaccine
* May complicate testing
* Core vaccine in North America
* Risk basis in the UK (horses travelling to endemic countries)
What three things does EHV-1 cause?
- Respiratory disease in young animals
- Abortion or Neonatal Death
- Equine Herpesvirus myeloencephalopathy
What is the pathology of equine herpesvirus?
Following respiratory tract infection (And/or reactivation of latently infected horses)
some virulent strains of EHV-1 demonstrate endotheliotropism
Endothelial cell replication and infection
Vasculitis and thromboischaemia of small arterioles
What two areas does EHV-1 affect?
Nervous System
» Ischaemic neuronal death
» Multifocal
» Myeloencephalopathy
**AND **
Uterus
Placental disease
Abortion/stillbirth
Foetal Infection
What are the signs of equine herpesvirus myeloencephalitis?
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
How might you Diagnose Equine Herpesvirus?
Nasal or nasopharyngeal swab PCR
* Serology (paired serology)
* Virus isolation
* CSF: Xanthochromic (yellow)
How might CSF analysis be useful?
Useful in diagnosis of CNS disorders
» Viral/bacterial encephalitis, meningitis, abscess, haemorrhage, neoplastic disease
» Cytologic analysis may help in treatment plan
How would you take different CSF taps?
Atlanto-occipital (AO) tap: requires short anaesthesia but relatively straightforward technique
» Lumbosacral tap: Standing sedation
» Standing cervical centesis: Ultrasound guided centesis of C1-C2
How might you treat Equine Herpes Virus?
Symptomatic
* NSAIDs, nursing, palatable feed, IVFT
* Anti-viral medication
* Valacyclovir
What is the prognosis for EHM?
Prognosis variable
* Better chance of full recovery if not recumbent
* If recumbent >24h: Grave prognosis
What is the difference between tetanus and botulism?
Clostridial neurotoxins inhibit neurotransmitter release
* The location at which they do this results in different clinical signs
* Tetanus: tetanic/spastic paralysis
* Botulism: flaccid paralysis
What is 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)
What do tetanus wounds look like?
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
What are the clinical signs of tetanus?
Localized stiffness – muscles around the 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/bradydysrhythmias * Miosis
What are the treatment goals for tetanus?
Eliminate C. tetani organism
* Penicillin or metronidazole
* Clean and debride wound
* Neutralise toxin
* Antitoxin: does not neutralise toxin that is already in nerve
* Give antitoxin BEFORE wound debridement
* Give tetanus vaccine (toxoid) to stimulate active immunity
How might you treat tetanus?
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
What is the tetanus vaccination?
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
What is the 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!
What are the three routes of entry for botulism?
- Ingestion of pre-formed toxin ‘forage poisoning’
* 2. Ingestion of spores, production of toxin in GIT,
* 3. C. Botulinum infection via wound
What are the clinical signs of botulism?
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
