Equine neurology, toxicology, myopathy (viral neuro diseases, EHV, rabies, cranial nerves, ataxia, WNV, poisonous plants, lead, myopathy) Flashcards
Which viruses have a primary neurotropism in horses? Which arbo viruses are associated with CNS disease in horses? Which cause neuropathy by damaging BBB?
Viruses with primary neurotropism: - Rabies - Borna virus Arbo viruses: - Eastern, Western and Venezuelan equine encephalitis - Japanese encephalitis - West Nile virus Damage BBB: - EHV-1, 4 - Equine Infectious Anaemia (EIA)
How are neurological viral diseases diagnosed in horses? Normal findings?
History:
- geographical location
- recent travel
- onset and duration
- other horses
- vaccination history
Clinical examination:
- fever
- normally symmetrical, multifocal or diffuse lesions
CSF analysis and serology:
- most commonly mononuclear pleocytosis and increased protein concentration
- culture, PCR, ELISA, IFAT to identify Ag or Ab
Medical imaging and functional testing:
- CT/MRI: usually non specific intracranial oedema
PM examination:
- Histopath: usually immunohistochemistry and/or PCT amplification necessary
Treatment for neurological viral diseases in horses?
Isolate (because fever + neurological signs = infectious unless proven otherwise!)
Quiet, dark stable with deep bedding and padded walls
Turn recumbent horses every 4-6 hours
Sling?
NSAIDs
Corticosteroids?
Antiviral therapy: acyclovir, valacyclovir
Ag-specific therapy: WNV
Vitamin E, thiamine
What do the different Equine Herpes viruses cause?
EHV-1: respiratory, abortion, myeloencephalopathy EHV-2: keratitis EHV-3: coital exanthema EHV-4: respiratory EHV-5: multi nodular pulmonary fibrosis EHV-6 to 8: donkeys
EHV-1: features of the virus?
Alpha herpes virus Specific to horses Enveloped capsid containing DNA genome Latent infections Humoral immunity is very short lived Naturally low Ab level May occur sporadically or as outbreaks
EHV-1 pathogenesis? Neurological signs?
Vasculitis and thrombosis of arterioles in brain and spinal cord (viral endotheliotropism)
May or may not show prior respiratory signs or fever
May be recent history of respiratory disease or abortion in the premises
Sudden onset and early stabilisation of signs
Signs:
- ataxia in hindlimb or all 4, or recumbent
- cauda equina signs: atony of bladder, flaccid tail and anus, perineal hypoalgesia
- occasionally show cranial nerve involvement
Diagnosis of EHV-1?
Virus isolation/PCR: - Nasal swab - Buffy coat - CSF Serology: - Complement fixation, ELISA - 4 fold rise in titre or >1:80 CSF: xanthochromia
Management of neurological EHV-1? Prevention?
Isolate
Prognosis reasonable with good nursing care
- better if nor recumbent
- recovery days-weeks (up to 1 year)
- poor prognosis if recumbent >24h
Recurrence of neurological signs not reported
Vasculitis: NSAIDs, corticosteroids, aspirin (anti-thrombotic)
Prevention: vaccination for EHV-1 and 4 (but ineffective against neurological form and possibly worsens case if given during neurological outbreak)
Rabies: Type of virus? Transmission? Pathogenesis?
Lyssavirus
Rhabdovirus family
Neurotrophic
Transmitted by saliva contaminated bite wounds
Uncommon in horses
Pathogenesis:
- Local inoculation at wound site
- Access to peripheral nerve
- Gradual movement centrally
- Replication in spinal/dorsal root ganglia
- Rapid spread in CNS (cord, brain, sympathetic trunk)
- Centrifugal spread down nerves (salivary glands)
- Incubation period very variable: 9 days - 1 year (depends on strain, host species, inoculum, proximity of inoculation to CNS)
Signs of rabies in horses?
No pathognomonic signs
From mild hindlimb lameness to sudden death
Signs depend on euro-anatomic location of pathology
Forms: Spinal -> paralytic form: - most common - localised hyperaesthesia: self mutilation of extremity/site of inoculation - progressive ascending: ataxia, weakness, lameness - recumbent 3-5 days Brain stem -> dumb form: - unusual in horses - depression - anorexia - head tilt, circling - ataxia - dementia/blindness - salivation/dysphagia - tail/penis/bladder paralysis - self-mutilation Cerebrum -> furious form: - unusual in horses - photophobia/hydrophobia - aggression/bizarre behaviout - hyperaesthesia - tenesmus - muscle tremors - seizures Forms can co-exist or progress
Rabies PM exam in horses?
Histology: eusinophilic inclusion bodies (Negri bodies) within neurones
Fluorescent Ab
Arbovirus groups A, B and C?
Arbovirus Group A: Togaviridae: - EEE, WEE, VEE Arbovirus Group B: Flaviviridae: - WNV: Hapanese encephalitis Arbovirus Group C: Bunyaviridae: - limited reports of infection in horses
Limitations to a neuro exam in horses?
Size
Behaviour/danger
Recumbency
Neuro exam in a horse?
From a distance: - Mentation - Behaviour - Posture Cranial nerves Observe and palpate neck and back: - muscle atrophy, asymmetry, sweating - range of movement - cervicofacial reflex - cutaneous trunci (panniculus) reflex) Tail: voluntary movement, tone Perineal reflex, tail clamp, anal tone Males: external genitalia Rectal exam: assess lumbar, sacral or coccygeal vertebrae, bladder volume and tone
What is cranial nerve I? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Olfactory nerve
Function: olfaction
Dysfunction: reduced or absent smell
Evaluation: difficult and subjective
What is cranial nerve II? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Optic nerve Function: vision Dysfunction: partial or complete blindness (dilated, unresponsive pupils) Evaluation: - vision (obstacles) - menace response (>2wks) - PLR - visual placing
What is cranial nerve III? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Oculomotor nerve Function: - pupil size - eyelid movement (ispilateral dorsal, ventral and medial recti, ventral oblique, elevator palpebrae) Dysfunction: - ventrolateral strabismus - inability to rotate eye dorsally, ventrally and medially - dilated unresponsive pupil - ptosis of upper lid Evaluation: - PLR - physiological nystagmus - eye position at rest
What is cranial nerve IV? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Trochlear nerve
Function: contralateral dorsal oblique muscle
Dysfunction: dorsolateral strabismus (fundic examination)
Evaluation:
- physiological nystagmus
- eye position at rest
What is cranial nerve V? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Trigeminal nerve
Function:
- sensory innervation of face
- motor innervation to masticatory muscles
Dysfunction:
- masticatory muscle atrophy and jaw weakness (dropped jaw if bilateral)
- facial hypo/anaesthesia
- neurotropic keratitis
Evaluation:
- size and symmetry of masticatory muscles
- sensory function (corneal, palpebral, nasal)
What is cranial nerve VI? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Abducens nerve Function: ipsilateral lateral rectus and retractor bulbi muscles Dysfunction: - medial strabismus - inability to move eye laterally and to retract eyeball Evaluation: - physiological nystagmus - eye position at rest - corneal reflex
What is cranial nerve VII? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Facial nerve Function: - motor to facial muscles - taste for rostral 2/3 of tongue - lacrimal gland Dysfunction: - drooping - inability to move ear and lip - absent blink - KCC Evaluation: - facial symmetry - palpebral reflex - menace response - corneal reflex - STT
What is cranial nerve VIII? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Vestibulocochlear nerve Function: - hearing - vestibular function Dysfunction: - partial or complete deafness - signs of vestibular disease Evaluation: - BAER - signs of vestibular disease: head posture, physiological nystagmus, gait, blindfold
What is cranial nerve IX? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Glossopharyngeal nerve Function: - motor to pharynx and palate? - sensory to caudal 1/3 of tongue and pharynx - salivary glands Dysfunction: - dysphagia - absent gag Evaluation: - gag
What is cranial nerve X? What is its function? What is seen with dysfunction? How can you evaluate it in horses?
Vagus nerve Function: - larynx, pharynx and oesophagus - all thoracic and abdominal viscera Dysfunction: - dysphagia - inspiratory dyspnoea - dysphonia - regurgitation - absent gag Evaluation: - gag - oculocardiac
What is cranial nerve XI? What is its function? What is seen with dysfunction?
Accessory nerve Function: - trapezius - part of sternocephalicus Dysfunction: trapezius atrophy
What is cranial nerve XII? What is its function? What is seen with dysfunction? Evaluation?
Hypoglossus nerve Function: motor to tongue Dysfunction: - tongue deviation/atrophy - problems with prehension Evaluation: - tongue size, tone and symmetry
Possible causes of an abnormal posture in horses?
Orthopaedic problem
Neurological:
1. Loss of spatial awareness - conscious proprioceptive deficits at rest, abnormal posture when stop/not correcting (don’t manipulate limb)
2. inability to move limb
Define ataxia? What to look for?
Subconscious proprioceptive deficits seen as irregular and unpredictable movement
Lood for poor coordination, swaying, limb moving excessively during swing phase (weaving, abduction, adduction, crossing limbs, stepping on self)
Exaggerated by tight circles, sudden stopping, backing, hills, raising head
