Eastern Equine Encephalitis (EEE): An ounce of prevention is worth a pound of cure
What is EEE?
The equine encephalitis viruses (EEV) are mosquito transmitted diseases that can cause severe inflammation of the brain (encephalitis) in horses and humans. As the names suggest, Eastern equine encephalitis (EEE) most commonly occurs in the Eastern United States and Canada. EEE is an arbovial, or vectorborne, disease that results in subclinical infections in birds. The virus is contracted from the host by mosquitoes during a blood meal and is then spread to other hosts by the mosquitoes. Both humans and horses are considered “dead end hosts”, meaning the virus cannot be spread from an infected horse or human to another horse or human. See Figure 1 for a more detailed explanation on how the virus is spread. Those at greater risk include people who engage in outdoor work and recreational activities in endemic areas are at increased risk of infection and people over age 50 and under age 15 seem to be at greatest risk for developing severe disease when infected with EEEV.
What are the symptoms of EEE?
Horses can develop an infection and low-grade fever within three days of acquiring the virus. The first visible signs usually appear within the first five days and consist of the following symptoms:
- Decreased appetite and depression
- Gait incoordination, hyperexcitability, teeth grinding, circling and head pressing. Some horses may lean against the wall or stand with their back legs crossed.
- Partial or total blindness may develop
- The progressively worsening neurologic disease often appears as severe to profound depression. Horses stand as if immobile with their heads hanging very low, their eyelids may become swollen and partly closed, their lips and tongue may be slack, often referred to as “sleeping sickness”.
- Terminally affected horses eventually become recumbent and comatose and frequently exhibit seizure activity prior to death.
These is no specific treatment for EEE. Most horses die within five days after the start of symptoms and mortality rates are commonly 70-90%, regardless of the level of supportive care. Those that do survive may have persistent neurologic signs and may not be suitable for riding.
How can I protect my horse from EEE?
Fortunately for horses, there are vaccines available to help protect against disease. Vaccinations against the EEE virus, as well as Western Equine Encephalitis (WEE) virus, are readily available and effective. Your horse should be vaccinated for EEE at least two times per year. Talk to your veterinarian about getting your horse vaccinated. Other preventative measures include reducing mosquito numbers and reducing mosquito access to your horse(s). Preventative measure include, but are not limited to:
- Managing and eliminating standing water. This includes water around barns, paddock areas, and pastures. You also want to check farm equipment, manage your ponds, clean water troughs regularly, and remove/empty any items that can collect water.
- Placing fans inside barns or stalls to maintain air movement, particularly in the early evening when mosquitos are most active.
- Housing horses indoors during peak mosquito activity increases (dusk and dawn).
- Turning lights off during the evening and overnight hours.
- Applying insecticide to individual horses (permethrin-based products are effective for this purpose) and use fly sheets in pasture areas.