Eastern & Western Equine Encephalitis: Causes, Symptoms, Prevention & Management
EEE/WEE are mosquito-borne viral diseases that attack the central nervous system. Here’s how infection happens, what to watch for, which tests your vet may run, how to time vaccination, and how to tighten your mosquito-control routine with Citraquin®.
Transmission & Incubation
EEE/WEE circulate between mosquitoes and birds. Horses are infected via mosquito bites and are considered dead-end hosts—they don’t shed enough virus to infect mosquitoes or other horses. Infections generally incubate for about 2–10 days before signs appear.
Context Longer vector seasons and shifting mosquito populations increase exposure windows—stack vaccination and barn control to stay ahead.
Early Signs & Neurologic Manifestations
- Early clues: fever, depression, reduced appetite, subtle behavior changes
- Neurologic signs: ataxia/incoordination, weakness, head pressing, circling, impaired vision, muscle tremors/fasciculations, seizures, recumbency
- Mortality: EEE carries a very high case fatality rate; WEE is typically less severe but still serious
Urgent Any rapidly developing neurologic sign is an emergency. Call your veterinarian immediately and keep the horse calm and safe while you wait.
Diagnosis & Testing
Serology (Antibody Tests)
IgM capture ELISA supports recent infection. Panels that include IgG/IgM help your vet interpret timing. Post-mortem brain testing confirms the diagnosis.
Advanced Testing
Your veterinarian may add PCR on appropriate samples or repeat serology to confirm trends. Testing and interpretation consider vaccination status and timing.
Vaccination (AAEP Core)
- Naïve adults: two-dose primary series 3–6 weeks apart
- Boosters: annually before mosquito season; semi-annual boosters may be advised in high-risk regions/classes
- Foals/broodmares: follow your veterinarian’s schedule and label guidance
Pro Tip Book boosters early so immunity is in place before peak mosquito pressure.
Mosquito Control (Citraquin®)
Layered Barn Strategy
- Eliminate standing water; clean tanks/buckets regularly
- Stable during dusk/dawn; run fans and use screens
- Manage weeds/brush; daily grooming checks after turnout
- Use fly gear as needed (sheets, masks)
Add Citraquin® to the Routine
Natural, citronella-powered repellent to help deter biting insects:
Apply per label directions as part of a layered plan alongside vaccination and environmental control.
Supportive Care & Prognosis
- Supportive care: anti-inflammatories, fluids, attentive nursing, sling support when needed, quiet housing to prevent injury
- Prognosis: varies by severity; EEE has a high fatality rate, and survivors of either disease may have lingering deficits
Comfort During Rehab
Keep conditioning comfortable with sensation-free, under-wrap friendly support:
Topicals do not treat EEE/WEE—they support comfort while your vet’s medical plan does the heavy lifting.
Rehab Basics
- Quiet environment; consistent handling
- Vet-guided return-to-movement (short, calm hand-walks if safe; progress slowly)
- Balanced farrier schedule; safe footing to prevent slips
EEE/WEE — FAQ
Are horses contagious to each other?
No. Horses are dead-end hosts and do not transmit EEE/WEE to other horses or to mosquitoes. The shared threat is mosquito exposure.
When should I vaccinate?
Work with your veterinarian to vaccinate before mosquito season each year. Naïve adults usually need two doses 3–6 weeks apart, then annual (or semi-annual in higher-risk scenarios) boosters.
What tests confirm EEE/WEE?
IgM capture ELISA supports recent infection; PCR on select samples and post-mortem brain testing can confirm. Your vet will interpret results alongside clinical signs and vaccine history.
How fast can EEE/WEE progress?
Signs can escalate quickly from fever and depression to neurologic deficits and recumbency. Early veterinary care improves the odds.
Will repellent alone protect my horse?
No single step is perfect. Stack strategies: vaccination, environmental control, stabling during peak mosquito hours, fans/screens, grooming checks, and a repellent like Citraquin® 32oz.
Educational note: This article is for general information and is not a substitute for veterinary diagnosis or treatment. Always consult your veterinarian for individualized care.
