Equine encephalitis is a viral disease primarily transmitted by mosquitoes. Doctors describe three main types of the disorder, Eastern, Western, and Venezuelan equine encephalitis. Each type results from a different viral agent, though all three can lead to similar symptoms. The most significant clinical finding in patients with equine encephalitis is inflammation of the brain and surrounding tissue. Some forms of the disease present relatively mild symptoms, such as fever and nausea, while others are potentially deadly. The disease cannot be cured, but doctors can administer medications and therapy to manage symptoms while the virus runs its course.

As the name of the condition suggests, equine encephalitis afflicts horses as well as humans and some other mammals. Mosquitoes can pick up the viruses involved in all three types from horses, and then transfer them to human hosts. People who live in warm, moist climates where mosquitoes thrive are at the highest risk of becoming infected.

The symptoms associated with equine encephalitis vary between individuals, but most infected people experience fevers, chills, headaches, and nausea for the first two to three days after exposure. Symptoms tend to worsen quickly as the virus reaches the brain, eventually leading to mental confusion, light-headedness, and dizziness. Without medical care, an individual may faint or even become comatose. All three types of equine encephalitis can lead to life-threatening complications, though the Eastern variety is much more deadly than the other two.

A person who becomes very ill or unresponsive should be brought to an emergency room immediately so doctors can make an accurate diagnosis and administer emergency medicine. Emergency room physicians can check for the viruses that cause equine encephalitis by collecting samples of blood and cerebrospinal fluid for careful laboratory analysis. Specialists may also perform diagnostic imaging scans of a patient's head to gauge the severity of encephalitis. After a diagnosis has been confirmed, the patient is usually hospitalized for careful monitoring and supportive care.

There are no set treatment measures for equine encephalitis. Like many viruses, the ones involved with this disorder evolve quickly to become resistant to any potential vaccines and antiviral agents. Treatment is geared toward keeping a patient's vital signs stable and trying to prevent permanent brain damage, acute respiratory failure, and cardiac arrest. Depending on the severity of the patient's symptoms, he or she may be placed on a mechanical respirator, given intravenous fluids, and injected with anti-inflammatory drugs. A person may need to stay in the hospital for several weeks for careful monitoring and ongoing treatment to ensure that his or her symptoms completely resolve.