27.6.4: Neurological horse - abnormal mentation

Question 1

Which of the following conditions are notifiable in the UK?
* Viral encephalitides: EEE/WEE/VE
* Viral encephalimyelitis: West Nile Virus
* Borna virus
* Leukoencephalomalacia

Answer 1

• Viral encephalitides: EEE/WEE/VE
• Viral encephalimyelitis: West Nile Virus

Question 2

General signs of forebrain disease

Answer 2

• Obtundation
• Head-pressing
• Odontoprisis (teeth grinding)
• Hyperstesia (irritability)
• Blindness (lack of menace response with normal PLRs)
• Seizures
• Circling
• Head turn
• Ataxia

Question 3

Depressed

Answer 3

animal is aware but not alert to surroundings/ not interested in normal stimuli

Question 4

Obtunded

Answer 4

animal is dull and slow to respond, but will respond appropriately

Question 5

Stuporous

Answer 5

animal is unresponsive to normal stimuli; can be aroused with strong stimuli

Question 6

Comatose

Answer 6

state of unconscious in which animal cannot be aroused, even with noxious stimuli

Question 7

Causative agent of Eastern/ Western/ Venezuelan encephalitides

Answer 7

Alphaviruses
These are zoonotic and notifiable!
Mainly present in N. and S. America.

Question 8

Clinical signs of viral encephalitides

Answer 8

• High fever
• All signs of forebrain disease
• Head tilt
• Muscle tremors

Question 9

Diagnosis of viral encephalitides

Answer 9

• 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

Question 10

Prognosis for viral encephalitides

Answer 10

• EEE: high mortality (75-95% die)
• WEE and VE: 50% death
• Residual damage is possible: central blindness, head tilt, facial paralysis

Question 11

Causative agent, epidemiology and transmission of West Nile Virus

Answer 11

West Nile Virus
* Neuroinvasive flavivirus transmitted by mosquitos (Culex pipiens )
* Seasonal disease first discovered in Africa but found worldwide
* Not in UK - notifiable !

Question 12

Where is West Nile Virus found?

Answer 12

• 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

Question 13

Incubation period of West Nile Virus

Answer 13

• Incubation period of 7-10 days
• 60% of horses are asymptomatic

Question 14

Clinical signs of West Nile Virus

Answer 14

• 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

Question 15

Diagnosis of West Nile Virus

Answer 15

• 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

Question 16

Pleocytosis

Answer 16

the presence of an abnormally large number of lymphocytes in the cerebrospinal fluid.

Question 17

Xanthochromia

Answer 17

the presence of bilirubin in the cerebrospinal fluid

Question 18

Characteristics and transmission of Borna virus

Answer 18

• Borna disease virus-1: neutrotropic virus
• Transmitted by contact with white-toothed shrew urine
• Long incubation period: ~2 months after inhalation of urine droplets

Question 19

Clinical signs of Borna virus

Answer 19

• All of those related to forebrain disease
• Fever
• Central blindness
• Chewing
• Swallowing deficits
• High mortality: 80%

Question 20

Diagnosis of Borna virus

Answer 20

• CSF: non-purulent inflammation (T-lymphocytes)
• IFAT or ELISA on CSF
• PM: Joest-Degen inclusion bodies on brain samples

Question 21

Treatment and prevention of Borna virus

Answer 21

• No vaccine available
• Most cases occur in Central Europe (endemic areas)

Question 22

Causative agent and characteristics of rabies

Answer 22

• Notifiable
• Neutropic virus belonging to genus Lyssavirus
• Zoonotic and fatal
• Must PTS and send head to authorised laboratory

Question 23

How does rabies spread through the body?

Answer 23

• Neuroaxonal migration with 2 replications: local at the site of the bite and CNS, then centripetal spread

Question 24

Incubation period of rabies

Answer 24

Variable: 10 days to several months

Question 25

Clinical signs of rabies

Answer 25

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.

Question 26

**True/false:** there is a vaccine available for Borna virus

Answer 26

**False** No vaccine currently available

Question 27

General points for control of viral encephalitides

Answer 27

* 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

Question 28

General supportive care for viral encephalitides

Answer 28

For mosquito-born and borna virus: * IV fluids * NSAIDs * Slings * Padding to avoid pressure sores

Question 29

Clinical signs of hepatic encephalopathy

Answer 29

* Depression * Obtundation * Head-pressing * Compulsive walking * Ataxia * Seizures

Question 30

Diagnosis of hepatic encephalopathy

Answer 30

* Liver enzyme elevation: SDH, GDH, GGT, AST, bile acids * If severe disease: hyperammonaemia, low BUN, prolonged clotting times (PT, APTT)

Question 31

Treatment of hepatic encephalopathy

Answer 31

* **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

Question 32

What diet should you feed a horse with hepatic encephalopathy?

Answer 32

* Low protein, high carbohydrate: sorghum, milo, beet pulp and molasses

Question 33

General principles of management of head trauma

Answer 33

* 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

Question 34

Cause of leukoencephalomalacia

Answer 34

* Fatal intoxication caused by ingestion of fumononisin toxins (mainly but not exclusively found on corn or corn by-products)

Question 35

Clinical signs of leukoencephalomalacia

Answer 35

* Obtundation * Ataxia * Compulsive walking * Head-pressing * Blindness * Acute onset and death within 7 days

Question 36

PM findings: leukoencephalomalacia

Answer 36

* Liquefactive necrosis and degeneration in subcortical white matter

Question 37

Key points in the approach to the horse with abnormal mentation

Answer 37

* 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