27.6.4: Neurological horse - abnormal mentation Flashcards
Which of the following conditions are notifiable in the UK?
* Viral encephalitides: EEE/WEE/VE
* Viral encephalimyelitis: West Nile Virus
* Borna virus
* Leukoencephalomalacia
- Viral encephalitides: EEE/WEE/VE
- Viral encephalimyelitis: West Nile Virus
General signs of forebrain disease
- Obtundation
- Head-pressing
- Odontoprisis (teeth grinding)
- Hyperstesia (irritability)
- Blindness (lack of menace response with normal PLRs)
- Seizures
- Circling
- Head turn
- Ataxia
Depressed
animal is aware but not alert to surroundings/ not interested in normal stimuli
Obtunded
animal is dull and slow to respond, but will respond appropriately
Stuporous
animal is unresponsive to normal stimuli; can be aroused with strong stimuli
Comatose
state of unconscious in which animal cannot be aroused, even with noxious stimuli
Causative agent of Eastern/ Western/ Venezuelan encephalitides
Alphaviruses
These are zoonotic and notifiable!
Mainly present in N. and S. America.
Clinical signs of viral encephalitides
- High fever
- All signs of forebrain disease
- Head tilt
- Muscle tremors
Diagnosis of viral encephalitides
- Clinical signs + time of year + location
- Serology: IgM titres
- CSF: neutrophilic inflammation (would see >50%, non-degenerate). Would also see high protein (>80 mg/dL)
- PM: RT-PCR formalin fixed
Prognosis for viral encephalitides
- EEE: high mortality (75-95% die)
- WEE and VE: 50% death
- Residual damage is possible: central blindness, head tilt, facial paralysis
Causative agent, epidemiology and transmission of West Nile Virus
West Nile Virus
* Neuroinvasive flavivirus transmitted by mosquitos (Culex pipiens )
* Seasonal disease first discovered in Africa but found worldwide
* Not in UK - notifiable !
Where is West Nile Virus found?
- Not in UK - Notifiable
- Recent outbreaks in Europe, evidence of persistent circulation in Mediterranean countries
- High risk for unvaccinated horses travelling to those areas in spring to autumn
Incubation period of West Nile Virus
- Incubation period of 7-10 days
- 60% of horses are asymptomatic
Clinical signs of West Nile Virus
- 60% of horses are asymptomatic
- Ataxia and limb weakness
- Muscle twitching esp around muzzle
- Obtundation
- Dog-sitting posture
- Thoracic limb knuckling
- Recumbency, circling
- Facial and tongue paralysis, head tilt
- Mortality around 31% in US studies
Diagnosis of West Nile Virus
- Clinical signs
- Serology (pay attention to vaccination)
- PCR on CNS tissue
- CSF analysis: mild pleocytosis with lymphocytes and macrophages, moderate elevation in protein and sometimes xanthochromia
Pleocytosis
the presence of an abnormally large number of lymphocytes in the cerebrospinal fluid.
Xanthochromia
the presence of bilirubin in the cerebrospinal fluid
Characteristics and transmission of Borna virus
- Borna disease virus-1: neutrotropic virus
- Transmitted by contact with white-toothed shrew urine
- Long incubation period: ~2 months after inhalation of urine droplets
Clinical signs of Borna virus
- All of those related to forebrain disease
- Fever
- Central blindness
- Chewing
- Swallowing deficits
- High mortality: 80%
Diagnosis of Borna virus
- CSF: non-purulent inflammation (T-lymphocytes)
- IFAT or ELISA on CSF
- PM: Joest-Degen inclusion bodies on brain samples
Treatment and prevention of Borna virus
- No vaccine available
- Most cases occur in Central Europe (endemic areas)
Causative agent and characteristics of rabies
- Notifiable
- Neutropic virus belonging to genus Lyssavirus
- Zoonotic and fatal
- Must PTS and send head to authorised laboratory
How does rabies spread through the body?
- Neuroaxonal migration with 2 replications: local at the site of the bite and CNS, then centripetal spread
Incubation period of rabies
Variable: 10 days to several months
Clinical signs of rabies
Paralytic rabies in horses (compared to dumb rabies in ruminants)
* Shifting lameness
* Mild colic
* Ataxia
* Loss of spinal reflexes: tail and anal paralysis, priapism, tenesmus
* Intermittent fever
Lethal within 10 days.
True/false: there is a vaccine available for Borna virus
False
No vaccine currently available
General points for control of viral encephalitides
- Vector-control: time-operated insecticide spray system in the barn
- Mosquitos feed from dusk to dawn: keep horses in stables at night with fly-screen windows
- Stall window fans -> midges are poor fliers
- Apply permethrin pour-on or any other fly repellant
- Rodent control in feeding rooms
General supportive care for viral encephalitides
For mosquito-born and borna virus:
* IV fluids
* NSAIDs
* Slings
* Padding to avoid pressure sores
Clinical signs of hepatic encephalopathy
- Depression
- Obtundation
- Head-pressing
- Compulsive walking
- Ataxia
- Seizures
Diagnosis of hepatic encephalopathy
- Liver enzyme elevation: SDH, GDH, GGT, AST, bile acids
- If severe disease: hyperammonaemia, low BUN, prolonged clotting times (PT, APTT)
Treatment of hepatic encephalopathy
- Treat liver disease and support neuronal function
- IV fluids with dextrose -> remember the liver is not functioning
- Oral lactulose and/or mineral oil -> reduced absorption of ammonia in GI system
- Sedation of cases with compulsive walking/ head pressing
- Avoid benzodiazepines as they increase GABA activity unless severe seizures
- Plasma transfusion if low clotting factors
- Could consider steroids
What diet should you feed a horse with hepatic encephalopathy?
- Low protein, high carbohydrate: sorghum, milo, beet pulp and molasses
General principles of management of head trauma
- Establish airway (nasal or frontal fractures)
- Obtain vascular access: hypotension, administer medication, control seizures
- Clean and dress wounds, staunch bleeding
- Antibiotics: prevent meningeal infection
- Padded helmet: avoid further trauma
- Control temperature: hyperthermia is possible with hypothalamic damage
- Control brain swelling: hypertonic saline, mannitol
- Oxygen, antioxidants (vitamin E, DMSO), steroids, NSAIDs, magnesium sulphate
Cause of leukoencephalomalacia
- Fatal intoxication caused by ingestion of fumononisin toxins (mainly but not exclusively found on corn or corn by-products)
Clinical signs of leukoencephalomalacia
- Obtundation
- Ataxia
- Compulsive walking
- Head-pressing
- Blindness
- Acute onset and death within 7 days
PM findings: leukoencephalomalacia
- Liquefactive necrosis and degeneration in subcortical white matter
Key points in the approach to the horse with abnormal mentation
- Neurolocalisation is important
- Most common causes in UK: head trauma, hepatic encephalopathy, (need to be aware of WNV)
- Initial treatment for all is supportive
- Initial diagnostics: bloodwork and serology
- Manage client expectations and give enough time
- Recommend WNV vaccines for all competition horses travelling to Europe for a summer
- Remain vigilant for emergent conditions
