Equine - encephalitis

Question 1

What is the structure of alphavirues (EEEV/WEEV/VEE)

Answer 1

• 11 kb (+) ssRNA
• enveloped with glycoproteins

Question 2

What are equine alphaviruses?

Answer 2

• characterized by CNS dysfunction and moderate to high mortality in horses
• Viruses genetically and antigenically distinct
• considerable antigenic diversity

Question 3

What is EEEV?

Answer 3

• Occurs in:
  
  • Eastern Canada, States East of the Mississippi River
  • AR, MN, SD, TX, MI, LA, MT,
  • Caribbean islands
• Clinical disease can occur in horses, humans, alpacas, llamas, cattle, swine, cats and dogs
• Enzootic in birds along east coat

Question 4

What is the mortality rate of EEEV in humans?

Answer 4

30-70%

Question 5

can humans/horses transmit EEEV?

Answer 5

no dead-end-hosts

low level viremias insufficient vector transmission

Question 6

What is WEEV?

Answer 6

• Occurs in:
  
  • western canada
  • States west of the mississippi river
  • Mexico and South america
• Associated with increased rainfall in early spring followed by warm temperatures
• Infrequent in US but circulates in wildlife

Question 7

Human mortality rate of WEEV

Answer 7

3-7%

Question 8

What is VEEV

Answer 8

• Occurs in South and Central America
• Not diagnosed in US for >40 years
• REPORTABLE
• associated with jungle/swampy areas
• all mammalian hosts capable of developing high-titer viremia for up to 5 days

Question 9

What makes VEEV different for EEEV/WEEV?

Answer 9

• enzootic in rodents (not birds)
• Horses and humans are NOT dead-end hosts - Amplify VEEV

Question 10

What is the human mortality rate of VEEV

Answer 10

• 10-35%

Question 11

What is the structure of Flaviviruses?

Answer 11

• 10kb (+) ssRNA
• Enveloped proteins

Question 12

What is WNV?

Answer 12

• Similar to EEEV/WEEV
  
  • more widespread
• horses and humans dead end hosts
• birds are reservoirs

Question 13

What is the human mortality rate of WNV

Answer 13

3-5%

Question 14

What are the clinical findings of Equine Arboviral Encephalomyelitis Viruses? (EEEV, WEEV, VEEV, WNV)

Answer 14

• Clinical signs similar and nonspecific
  
  • depression, reduced activity, fever, decreased appetite
• Infections may be subclinical
• Progression and severity of disease is different between viruses
  
  • More: EEEV and VEEV
  • Less: WEEV and WNV
• Neurologic signs typically occur 9-11 dpi
  
  • may have shorter incubation with EEEV/VEEV (5dpi)
  • “sleeping sickness”

Question 15

What are neurologic signs that are more common with EEEV and VEEV?

Answer 15

• Altered mentation, blindness, restlessness, hypersensitivity, head pressing, circling, dysphagia, irregular ataxic gait, paresis and paralysis, seizures and death
• symmetric ataxia affecting all limbs, progresses to quadriparesis
• Many progress to recumbency 12-18 hrs after onset of neurological signs
• death within 2-3 days of clinical onset (EEEV)

Question 16

What are the WNV clinical signs?

Answer 16

• Variable
• May present as neurologic abnormalities, colic, lameness, anorexia, fever, depression
• Neurologic abnormalities may vary
  
  • >90% Spinal cord disease
    
    • asymmetric, multifocal or diffuse ataxia and paresis
    • forelimb, hindlimb, unilaterally or a single limb
  • 40-60% behavioral changes, mental aberrations
    
    • hyperesthesia with fractious reactions to aural, visual, and tactile stimuli
  • 60-90% Fine and course tremors of face and neck
  • Urinary dysfunction (infrequent)

Question 17

What clinical findings can be found in all viral encephalomyelitis? (WEEV/ WNV/ EEEV/ VEEV)

Answer 17

• Cranial nerve deficits
  
  • weakness or paralysis of the face and tongue
    
    • dysphagia, quidding, esophageal choke, nystagmus
• facial edema due to lowered head, depression
• Trauma due to seizures, neurologic dysfunction
• secondary morbidities due to recumbency

Question 18

What gross lesions are common with EEEV/VEEV

Answer 18

widespread and prominent congestion of the meninges

Question 19

What gross lesions are common with WEEV/WNV

Answer 19

small multifocal areas of discoloration and hemorrhage throughout the brain and spinal cord

Question 20

What are the microscopic lesions of equine encephalitis viruses

Answer 20

• Meningoencephalitis
  
  • varying amounts of vasculitis, necrosis, hemorrhage, inflammatory cell infiltrate (neutrophils and mononuclear cells)
  • often multifocal

Question 21

How is equine viral encephalitis diagnosed?

Answer 21

• Viremia typically resolved by the time of neurologic sings
• Serologic tests
  
  • IgM capture ELISA
  • neutralizing Ab titers; IgG paired samples
• CSF analysis (increased WBC and proteins) PCR
• Postmortem: IHC, PCR, Virus isolation
  
  • Test for rabies in ALL horses with encephalitis

Question 22

How is equine viral encephalitis treated?

Answer 22

• Control pain and inflammation
• Prevent injuries and trauma
• Supportive care

Question 23

What is the prognosis for equine viral encephalitis?

Answer 23

• Poor prognosis if persists to recumbancy
• Mortality in hoses showing clinical signs:
  
  • EEEV 50-90
  • WEEV 20-50
  • VEEV 50-75
  • WNV 35-45
• Can have residual neurologic deficits even after recovery
  
  • EEEV/VEEV/WEEV >>>>>WNV

Question 24

What vaccine exists for Equine viral ecephalitis?

Answer 24

• AAEP - Core vaccine includes EEEV, WEEV, WNV
• EEEV/WEEV
  
  • inactivated adjuvanted whole virus
• WNV
  
  • Inactivated adjuvanted whole virus
  • Non-replicating adjuvanted vector vaccine
  • Inactivated adjuvanted vector vaccine
• Initial series of 2 vaccinations 4-6 wks apart