neurology 1 pt 2 Flashcards
(28 cards)
viral diseases effecting the equine brain? importance?
- Alphaviruses – EEE/WEE/VEE
- Flavivirus - WNV
- Lyssavirus – Rabies
- All are reportable
New World Alphaviruses
- structure
- environmental sensitivities
- what viruses in this category?
- Single strand, positive sense RNA, enveloped
- Sensitive to drying & UV radiation
- The viruses:
> Eastern Equine Encephalitis virus (EEE)
> Western Equine Encephalitis virus (WEE)
> Venezuelan Equine Encephalitis virus (VEE)
EEE/WEE/VEE
- how do we diagnose / differentiate?
- Viral species
> Differentiated by Hemaglutination Inhibition (neutralizing
specificity) - Fluorescent Antibody test
- Complement Fixation test
- ELISA!
- PCR!
Eastern Equine Encephalitis
- importance
- geography
- age affected
- Major concern
- Primarily southeast USA
- Occurs in Canada, northern states
- Florida – most cases are unvaccinated or only initial vaccine dose administered
- Usually < 3-years-old
EEE viral cycling, hosts
mosquitoes > birds > mosquitoes > birds….. cycle
- but sometimes those mosquitoes bite horses or humans!
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Sylvatic cycle - Passerine birds (eg. songbirds)
- Ornithophilic mosquitos
> Culiseta melanura - Non-avian transmission
> Culex erraticus - “Dead end hosts” – horses, humans, other mammals (low viremia)
- Snakes
EEE clinical syndrome categories, by signs
- Inapparent infection, fever
- Generalized febrile illness, anorexia, depression, tachycardia, diarrhea
- Encephalomyelitis – esp young horses; usually assoc. with second febrile crisis. Death in 2-3 days.
> (rapidly progressive, high mortality rate)
EEE pathogenesis
- Access to body, replicate in lymph nodes, spread – hematogenous & neuronal
- Large strain variation as to virulence
- Reservoir hosts – usually subclinical infection
- Many horses & humans – subclinical infection
- Incubation period 2-3d up to 3 weeks
EEE – Clinical Signs
Obtunded, stupor
Ataxia
Paralysis
Incoordination
Circling
Staggering
Recumbency
Anorexia
Irregular gait
Teeth grinding
Head pressing
Hyper-excitable
Seizures
Death
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Not all infected animals develop signs of disease; a horse may be infected with the virus, develop antibodies to it, and eliminate the virus without showing any obvious signs of illness.
EEE clinical course
- how does it compare to WEE, VEE
- 2 – 14 days
- EEE – most die or euthanized
- WEE, VEE – may survive
EEE DDx
- Alphavirus
- WNV
- Rabies
- EHV-1
- EPM
- Wobbler Syndrome
- Leukoencephalomalacia
EEE diagnostic tests
- Complete blood count
- Serum biochemistry profile
- CSF!!
> Increase protein level
> Increased nucleated cell count (mononuclear) - Viral testing serology – live animal with fever
- IgM - >1:400 suggests recent infection
- Necropsy – brain tissue
EEE pathologic findings
- Necrotizing encephalitis w neuronal dysfunction
- Neuronal necrosis, neurophagia
- Marked perivascular cuffing (mono & neuts)
- Focal & diffuse microglial proliferation
- Gray matter lesions > white matter lesions
- Most marked: cerebral cortex, thalamus, hypothalamus.
- Spinal cord – mildly affected (cervical > lumbar)
EEE treatments
- None
- Empiric/supportive
> Corticosteroids
> Diuretic (Mannitol)
> Sedation – detomidine - Humans – alpha-interferon
EEE control
- Vaccination!!!
> Adequate initial series
> Annual or biannual boosters - Mosquito control
WEE
- traditional geography
- other strains?
- outbreaks?
- “West of the Mississippi River”
- Does occur east of the Mississippi River
- Other strain: Highland J virus – less pathogenic
- Limited sporadic outbreaks in horses
VEE
- types?
- outbreaks?
- Exotic disease
- At least 6 different types
> Epidemic forms – IAB, IC, IE
> Endemic forms:
=> ID– Central America
=> IF– Brazil
=> II – Florida
=> III – VI elsewhere - Large outbreaks in horses & humans (always occurs at
same time)
West Nile Virus
- virus family
- what is causes, in who?
- hosts?
- Family – Flaviviridae
- Genus – Flavivirus
- Positive-sense, single stranded RNA
- Encephalitis – horses, humans, other mammals
- Bird – mosquito cycling, other
- Horses & humans – “dead end” hosts
- May infect >300 species of birds
‘sentinels’ for West nile virus
- May infect >300 species of birds
- House sparrow – amplifying host
- Corvids (eg. Crows) – high mortality > tips us off that something is wrong
WNV
- seasonality
- signalment?
- Seasonality – July → October
- No breed or sex predilection
WNV signs
- what is unique?
- prognosis?
- Usually acute onset, rapid progression
- Brain & spinal cord
- Behavioral/mentation change
- Muscle fasciculations > We don’t see this with other similar diseases! good for differentials!
<><><><> - Non-specific – fever, inappetance, depression
- Colic, lameness
- Progression of brain & spinal cord signs
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Prognosis - 30% mortality (die or euthanized)
- Survivors – 90% may become normal
WNV
- Dx
- prevention
Diagnosis
- Geographic area
- Vaccination status
- Ancillary testing
> IgM capture-ELISA
> CSF
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Prevention
- Vaccination – many types of vaccines
- Mosquito control
Rabies
- type of virus?
- who gets it?
- transmission
- stains
- Family Lyssavirus
- Genus Rhabdovirus
- Negative strand RNA virus
- Disease of mammals
- Passed by animals with clinical signs (or near)
- Strains: Fox, bat, raccoon
rabies clinical signs, forms, clinical course
- Any signs that are acute, severe, rapidly progressive intracranial disease.
- Plus – autonomic instability, dysphagia, paresis, paresthesia, hydrophobia
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Forms: - Dumb: mentally depressed
- Furious: hyperexcitable, fearful, enraged
- Paralytic: flaccid paraparesis, tetraparesis, tetraplegia
<><><><> - Shifting lameness
- Ataxia
- Colic
- Decreased to absent reflexes
- Progressive CNS signs
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Clinical course – 1-8 days; may die acutely
rabies incubation
- Few days to 6 months
- Depends on where bitten
