Viral Encephalitic Disease

What genus are EEE, WEE, and VEE?

Alphavirus

What genus is WNV?

Flaviviridae

What family are EEE, WEE, VEE, and WNV?

Togaviridae

Where is WEE located?

Not in US

Where is EEE located?

Coastal atlantic, SE US, MI, and TX

Where is VEE located?

Central and south america

How are EEE and WEE maintained?

Cycling between birds and mosquitoes

What is an overwintering host for EEE?

Snakes

What are the amplifying hosts of EEE and WEE?

Birds

What are the dead end hosts of EEE and WEE?

Horses

How is VEE maintained?

Mosquitoes and small odents

What are the amplifying hosts of VEE?

Horses

When do EEE and WEE pop up?

Epizootic for 1-3 months in the summer and fall (favors mosquitoes)

What are the C/S of the viruses?

Inapparent infection with low-grade viremia and fever

Generalized febrile illness with anorexia, depression, tachycardia, and diarrhea

Clinical encephalomyelitis (classic form)

What horses are most susceptible to viral encephalitis?

Young

What virus is more severe and rapidly progressive CS?

EEE

What is the localization of the viruses?

Initially cerebral and progresses caudally to brainstem and spinal cord (EEE)

What are the cerebral signs of viral encephalomyelitis?

Obtunded mentation

Head pressing

Hyperesthesia

Compulsive walking

Blindness/lack of menace

What are the brainstem signs of the viruses?

Abnormal PLR, head tilt, nystagmus, facial and tongue paralysis

What are the spinal signs of the viruses?

Ataxia and paresis

What is on CSF of EEE?

High protein and cell count

Neutrophilic pleocytosis

What is on CSF of WEE?

High cell count

Lymphocytic pleocytosis

What blood work changes can you see?

Leukocytosis

Hyperfibrinogenemia

How do you diagnose the viruses?

Serology with hemagglutination-inhibition or plaque reduction neutralizing titer (need a 4 fold rise between acute and convalescent)

IgM capture (MAC) ELISA to DIVA

What is a human health hazard of the viruses?

CNS tissue

How do you diagnose the viruses on necropsy?

Virus isolation, IHC, or PCR of brain tissue

Meningoencephalomyelitis multifocal to diffuse

What infiltration is present with EEE?

Neutrophilic

What infiltration is present with WEE?

Lymphocytic

How do you treat the viruses?

Cerebral inflammation

Cerebral edema

Supportive care

What supportive care should you provide for the viruses?

IV fluids, nutritional support

Prophylactic antibiotics

Control hyperthermia

Slinging

Limb bandages

Sedation as needed

How do you control cerebral inflammation?

Steroids AND NSAIDs (never do in small animals)

What usually causes mortality from the viruses?

Laceration, head trauma, fracture, contaminated joints

What is the prognosis of EEE?

Highest mortality of 75-95% with 2/3 of survivors having residual CNS signs

Treatment is ineffective with EEE

What is the prognosis of WEE?

19-50% mortality with most recoveries being very good

What is the mortality of VEE?

19-83% mortality with slow improvement if they survive

how do you prevent EEE and WEE?

AAEP core vaccines before onset of mosquito season annual or biannual depending on mosquito activity

Mosquito control

Quarantine VEE infected horses

How do we control Venezuelan encephalitis?

No disease in over 20 ears but there is a MLV vaccine that can be conditionally released

What is the public health significance for the viruses?

Zoonotic and humans can die or can be subclinical, febrile, or neurologic

Horses are amplifying hosts for VEE

What species can also get EEE?

New world camelids, emus, pigs

What species can get VEE?

Pigs, domestic rabbits, goats, dogs, sheep

What type of virus is WNV?

Positive ssRNA

How is WNV transmitted?

Classic vector with birds amplifying and mosquitoes transmitting with humans and horses ad dead end hosts

What is the incidence of WNV?

Coincides with vector availability

Seasonal in temperate regions

Year round in subtropical or tropical areas

What are the C/S of WNV?

Fever, anorexia, depression with sudden onset and progression of neurologic signs

Muscle fasciculations

Changes in personality

Gait abnormalities: lameness, ataxia, weakness

CN abnormalities for short periods

What is on clin path with WNV?

Mild lymphopenia

Elevated muscle enzymes

What is on CSF of WNV?

Increased mononuclear cell population

Elevated protein

Xanthochromic (yellow)

How do you diagnose WNV?

IgM capture ELISA (DIVA)

Plaque reduction neutralization test

What in the brain does WNV attack?

Grey matter

How do you confirm WNV postportem?

PCR

IHC of CNS tissues

Polioencephalomyelitis

CNS TISSUE IS HUMAN HEALTH HAZARD

how do you treat WNV?

Treat cerebral inflammation and edema with flunixin

Supportive care with low dose steroids if needed

Anti-virals with interferon alpha or high immunoglobulin WNV plasma

What is the prognosis for WNV?

22-30% mortality with recumbency being a negative prognostic indicator

Full recovery can take weeks to months and residual weakness and ataxia is common

30% will lead to complete paralysis of one or more limb

What are the public health considerations for WNV?

Zoonotic from mosquitoes or post-mortem exams

no human vaccine

What other species get WNV?

New world camelids (can vaccinate)

Squirres

What is the family and genus of rabies?

Rhabdoviridae Lyssavirus

What type of virus is rabies?

Enveloped ssRNA

What is the natural reservoir of rabies?

Wildlife with each strain maintained by a particular reseroir host

What happens with wildlife-adapted rabies strains?

Die out when passed into a species it is not adapted to

how is rabies transmitted?

By saliva contaminated wounds

What is the pathophysiology of rabies?

SQ or intradermal inoculation

Replicates locally

Binds to Ach receptors of peripheral nerves and migrates retrogradely to CNS

Virus replication in cell bodies of CNS

Spreads centrifugally along rootlets of cranial nerves to salivary glands and nasal epithelium

Where is rabies endemic?

US, Canada, Europe

When is rabies a differential?

Any acute, rapidly progressive intracranial disease especially if there is autonomic instability, dysphagia, hydrophobia, paresis, paresthesia

What is the furious form of rabies?

Cerebral

What is the dumb form of rabies?

Brainstem

What is the spinal form of rabies?

Paralytic

What is the most common type of rabies in horses?

Paralytic (spinal form)

What are the C/S of the cerebral / furious form of rabies?

Aggressive, photophobia, hydrophobia, hyperesthesia, straining, muscular tremors, convulsions/seizures

What are the C/S of the brainstem or dumb form of rabies?

Depression, anorexia, head tilt, ataxia, dementia, excess salivation, facial and pharyngeal paralysis, blindness, flaccid tail and anus, urinary incontinence, self-mutiliation

What are the C/S of paralytic or spinal form of rabies?

Progressing ascending paralysis

Ataxia

Shifting lameness with hyperesthesia and self-mutilation of extremity

Recumbent in 3-5 days

What are some horse specific rabies C/S?

Highly variable

Can have fever, hind limb lameness, hyperesthesia, progression to paresis

Mentation normal until end-stage

MST is 4 days

Fatal after clinical course in 1-8 days due to cardiorespiratory failure

What is a major concern with rabies?

Zoonotic, USE PPE

How do you diagnose rabies?

CSF can be normal or have moderate mononuclear pleocytosis and increased protein

Necropsy with nonsuppurative meningoencephalomyelitis and definitive testing

How do you definitively diagnose rabies?

Direct or indirect fluorescent antibody (DFA is standard)

Hippocampus, cerebellum, brainstem, pons, or medulla with negri bodies on histopath is suggestive

If inconclusive IFA then do intracerebral inoculation of mice with CNS tissue

How do you treat rabies?

No treatment just supportive care and PPE if attempting treatment

How do you prevent rabies?

AAEP core vaccine that is given annually with an inactivated virus with adjuvant

how can you prevent WNV?

AAEP core vaccine before mosquito season

Mosquito prevention and control

What types of WNV vaccines are there?

inactivated whole virus vaccine

MLV canarypox vector vaccine with prM and E proteins

Liv flavivirus chimeric YF17D vector vaccine with prM and E proteins