Infectious neurological disease

Question 1

Vector borne neurological diseases

Answer 1

West nile virus

Eastern equine encephalitis (EEE)

Western equine encephalitis (WEE)

Venezualan equine encephalitis (VEE)

Japanses encephalitis

Equine encephalosis virus (EEV)

Tick borne encephalitis

Neuroborreliosis/lyme

Question 2

Parasitic neurological diseases

Answer 2

Equine protozoal myelitis (EPM)

Halicephalobus gingivalis

S. vulgaris (migration)

Trypanosomiasis

Draschia megastoma

Question 3

Viral neurological diseases

Answer 3

EHV-1

Rabies

Hendra/Nipah

Borna disease

Aujesky’s (rare/unlikely)

Equine infectious anaemia (EIA)

Question 4

Toxic neurological infections

Answer 4

Tetanus

Botulism

? Equine Grass sickness

Question 5

Bacterial neurological diseases

Answer 5

Bacterial meningitis

Question 6

Clostidial disease in horses

Answer 6

Tetanus and botulism

Clostridial neurotoxins inhibit neurotransmitter release

Bind to negatively charged molecules on nerve terminal

This complex binds to a protein on nerve terminal surface

Then it is internalised:
○ Tetanus toxin migrates retrograde (motor neuron -> spinal cord -> brainstem)
○ Botulinum toxin stays at NMJ

Question 7

Tetanus in horses

Answer 7

Clostridium tetani

Gram positive, obligate anaerobe

Spore forming

Ubiquitous in soil/faeces

Forms three toxins: tetanospasmin and tetanolysin most important

Antibodies to tetanospasmin are protective

Question 8

Clinical signs of tetanus in horses

Answer 8

Third eyelid protrusion

‘Saw horse’ rigid stance

Raised tailhead

‘Lock jaw’

Dysphagia

Hyperaesthesia

Autonomic signs
§ Tachy/bradydysrhythmias
§ Miosis

Question 9

Prognosis of tetanus in horses

Answer 9

very guarded

Better if identified and treatment started early in course of disease

Question 10

Treatment of tetanus in horses

Answer 10

Eliminate C. tetani organism

Antimicrobials

Neutralise toxin

Give tetanus vaccine (toxoid) at distant site

Control muscle spasm

Question 11

How to eliminate C.tetani organism from a horse

Answer 11

§ Clean and debride wound (if you can find one)
§ Aiming to create an aerobic environment

Question 12

Antimicrobials for tetanus infection

Answer 12

§ Penicillin vs. metronidazole

§ Penicillin may act as a competitive inhibitory neurotransmitter as is similar in structure to GABA -> may worsen disease by blocking GABA

§ Metronidazole is superior in human studies

Question 13

Tetanus antitoxin

Answer 13

§ Antitoxin: does not neutralise toxin that is already bound

§ Give antitoxin BEFORE wound debridement

§ Consider intrathecal antitoxin early on

Question 14

How do you control muscle spasm in tetanus infection

Answer 14

§ Drugs like methocarbamol and diazepam can be used

§ ACP (not hugely effective), alpha 2 agonists

Question 15

Nursing for tetanus infection

Answer 15

Padded stable ideal or anaesthetic induction box
§ May need slinging so consider winch access

Minimise stimulation
§ Cotton wool in ears
§ Low light/noise

Nutritional support and hydration

Manual evacuation of rectum and bladder

Question 16

Tetanus vaccination

Answer 16

Tetanus toxoid

Start at 6mo of age
§ Vaccinate mare in last trimester to confer immunity via colostrum

Two vaccines four weeks apart, then varies according to product license

Question 17

Tetanus antitoxin

Answer 17

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

Often given to foals at first examination
§ Consider maternal antibodies/whether mare vaccinated

Comes in big bottles, is expensive… and needs to be discarded soon after opening despite containing several doses

Therefore, in reality fewer people using at all/often used inappropriately

Question 18

Botulism in horses

Answer 18

Rare in the UK, USA has a higher prevalence

8 different serotypes based on toxin produced (A to G)
○ Different geographic regions associated with different serotypes
○ Affects treatment

Question 19

Clinical signs of botulism in horses

Answer 19

Weakness, flaccidity

Ptyalism, loss of tongue tone

Cranial nerve deficits – dysphagia, ptosis

Trembling, sweating, increased respiratory effort

Reduced parasympathetic activity -> decreased GIT motility

Progress to recumbency

Death may occur due to paralysis of respiratory muscles

Question 20

Three mechanisms of botulism infection in horses

Answer 20

Ingestion of preformed toxin

Bacterial infection of wound/umbilicus in foals

Ingestion of spores

Question 21

Botulism- ingestion of preformed toxin

Answer 21

Poorly preserved hay/haylage/silage

Animal remains in feed often implicated

Question 22

Botulism - infection of wound/umbilicus in foals

Answer 22

Serotype B, toxin produced in wound

Question 23

Botulism - ingestion of spores

Answer 23

go on to produce toxin in the GI tract

Causes ‘shaker foal syndrome’

Serotype B, affects foals 2 weeks – 8 months old

Question 24

Pathogenesis of botulism

Answer 24

three mechanisms of initial infection

-> haematogenous spread of toxin

-> Toxin binds to nerve terminal

-> block ACh release at NMJ

-> flaccid paralysis

Question 25

Diagnosis of botulism

Answer 25

History spoiled feed Clinical signs Laboratory tests challenging/unreliable

Question 26

Treatment of botulism

Answer 26

Nursing Supportive/symptomatic treatment Botulinum antitoxin – need the correct serotype - Significant association with survival

Question 27

Prognosis of botulism

Answer 27

Median time of hospitalisation for survivors = two weeks Pneumonia, decubital ulcers, corneal ulcers… 48% survived - 67% that arrived at the hospital standing survived - 95% that remained standing during treatment survived

Question 28

Equine Herpesvirus myeloencephalitis (EHM)

Answer 28

EHV-1 (Alphaherpes virus) ○ Usually causes respiratory disease ○ May cause abortion or neurological disease EHV is ubiquitous ○ Certain strains more neurotropic Causes vascular infarction/thrombosis Ischaemic/haemorrhagic degeneration

Question 29

Signs of Equine Herpesvirus myeloencephalitis (EHM)

Answer 29

(background respiratory dz) Pyrexia, dull, inappetent – viraemic phase Sudden onset neurological signs Ataxia – hindlimb > forelimb Caudal spinal cord segments; § Bladder distension and urinary incontinence § Penile protrusion in males § Flaccid tail and anus

Question 30

Diagnosis of Equine herpesvirus myoencephalitis (EHM)

Answer 30

Clinical signs Nasopharyngeal swab PCR Serology (paired) Virus isolation CSF xanthochromic/yellow

Question 31

Treatment of Equine herpesvirus myeloencephalitis

Answer 31

If they survive may have neurological deficits for life and prolonged recovery times Better prognosis if recover quickly and remain able to stand § Some take months to improve § May have permanent neurological deficits Mortality rate but may be high (30-50%) Can be prolonged recovery time Prognosis worse if they become recumbent

Question 32

Vaccination for Equine herpes virus myeloencephalitis

Answer 32

Routine vaccination of at-risk populations helps to minimise outbreaks Vaccination doesn’t protect against EHM - reduces environmental load Do not vaccinate at-risk horses in the face of an outbreak

Question 33

Biosecurity in EHV-1 outbreak

Answer 33

Keep groups small, separate pregnant animals etc. on premises Isolate new arrivals for 3 weeks, monitor temperatures During outbreak: § Isolate in contacts § Take temperature twice daily, separate staff and shower/change clothes, no through-traffic, separate stable tools § No movement on or off premises

Question 34

West Nile Virus

Answer 34

Zoonotic and notifiable Flavivirus Not in the UK yet, but we have the vectors Horse is a dead-end host, as are humans Vector borne via mosquitoes, birds are an amplifier host Most infected horses won't display clinical signs

Question 35

Clinical signs of West Nile virus

Answer 35

Dull/lethargic Facial paralysis, dysphagia Muscle fasciculations Hyperexcitability Ataxia Recumbency

Question 36

Diagnosis of West Nile Virus

Answer 36

IgM capture ELISA

Question 37

Treatment of West Nile Virus

Answer 37

No specific treatment

Question 38

Vaccination for West Nile Virus

Answer 38

From 5mo of age (possibly younger) Reduces severity of disease and viraemia May complicate testing (but IgM response after vaccination considered ‘infrequent’ so vaccines are largely compatible with IgM capture ELISA testing)

Question 39

Neuroborreliosis

Answer 39

Zoonotic Lyme disease Borrelia burgdorferi – spirochete bacteria Transmitted by ixodes ticks Seropositive horses high in healthy population so caution with diagnosis

Question 40

Clinical signs of Neuroborreliosis

Answer 40

Muscle atrophy/weight loss, cranial nerve dysfunction, ataxia, behavioural change, uveitis, pyrexia, joint effusion/shifting lameness

Question 41

Diagnosis of neuroborreliosis

Answer 41

Positive antibody titre (PCR OspA antigen) If have joint effusion can attempt to test synovial fluid, or stain with silver stains and manually look for spirochetes

Question 42

Treatment of Neuroborreliosis

Answer 42

Prolonged (months) tetracyclines Typically start with intravenous oxytetracycline then move to oral doxycycline (unlicensed)

Question 43

Equine protozoal myeloencaphalitis

Answer 43

Not usually a DDx in UK Protozoal disease - Sarcocystis neurona and Neospora hughesi Increased risk at times of stress White and grey matter affected at any site in CNS so signs vary

Question 44

Rabies in horses

Answer 44

Zoonotic and notifiable Not present in the UK, but notifiable so important to be aware of it Lyssavirus, may affect any mammal Fatal Variable incubation period (2 weeks -> several months) Variable clinical signs, progress rapidly (ataxia, pyrexia, colic, lethargy, self-mutilation, aggression…) Cannot test pre-mortem Vaccination programs successful

Question 45

Western/Easter/Venezuelan Equine encephalitis

Answer 45

Zoonotic and notifiable Exotic to the UK but notifiable – need to be aware may be a DDx if there’s a history of travel, but you’re very unlikely to see it Togaviral encephalitis Primary reservoir birds/rodents – horses are sentinel hosts Therefore incidence of equine cases useful to predict human risk Zoonotic – fatal

Question 46

Clinical signs of Western/Eastern/Venezuelan Equine Encephalitis

Answer 46

Pyrexia, dull, circling/head pressing, dysphagia, paralysis… Death