Equine encephalitis:

Syn: Equine viral encephalomyelitis, Equine sleeping sickness

• It is a infectious viral disease affecting horses.
• It is characterized clinically by signs of deranged consciousness, molar irritation and paralysis.

Etiology:

• α-virus of Togaviridae family
• virus have three strains; eastern, western, Venezuelan
• eastern strain is most virulent whereas western is less.
• Horses, Donkey, Mule, Monkey and Man are naturally affected.

Epidemiology:

• These viruses are endemic to North, Central or South America
• The North American variant is the most pathogenic and is found in eastern Canada, all US states east of the Mississippi River, Arkansas, Minnesota, South Dakota, Texas; and in the Caribbean islands. The South American variant, now called Madariaga virus (MADV), is less pathogenic and is confined to Central and South America.
• EEEV is perpetuated in a sylvatic cycle between avian hosts (passerine birds) and mosquitoes, with primary transmission in this cycle via Culiseta melanura.
• Snakes have been identified as a possible reservoir.
• Young horses are more susceptible. Disease mostly occurs in mid and late summer.
• Incubation period; 1-3 days in EEE, 2-4 days in WEE, and 1-6 days in VEE

Transmission:

• Disease is primarily transmitted through bite of insects, i.e. mosquitoes, ticks, bugs, mites and lice.

Pathogenesis:

• Virus gains entry through bite of mosquitoes
• After entry, they replicate at entry sites including dendritic cells
• Dendritic cells transport virus to regional LN
• It is followed by primary viremia
• Virus then invades extraneural fissures, multiplies leading secondary viremia.

Clinical Signs:

• Initially fever with anorexia, depression
• Temperature increases upto 24-48 hours (106°F). Nervous signs occurs at peak of temperature rise.
• Abnormally wide stance, hanging head, dropping ears, flaccid lips
• Aimless walking, central blindness
• Inability to swallow, photophobia, circling, yawning, grinding of teeth
• Constant head pressing against a corner or stall or fence is typical presentation.
• Death occurs within 2-3 days after onset of clinical signs

Diagnosis:

• Isolation and identification of virus
• HI, CFT, VNT, ELISA
• PCR

Treatment and Control:

• There is no effective antiviral treatment available for disease. Supportive care is advised.
• To control pain; flunixin meglumine @1.1 mg/kg, b.wt. IV every 12 hours upto 5 days
• Phenobarbitone or Diazepam to control convulsion.
• Hyperimmune serum 500 ml, IV
• Neurobion; B₁₂ injection 3000 mcg @ 1-2 mL, IM or SC
• Vaccination; Live attenuated vaccine used intradermally.