Eastern Equine Encephalitis

Eastern Equine Encephalitis



Eastern equine encephalitis virus (EEEV) is transmitted to humans by the bite of an infected mosquito. Eastern equine encephalitis (EEE) is a rare illness in humans, and only a few cases are reported in the United States each year. Most cases occur in the Atlantic and Gulf Coast states . Most persons infected with EEEV have no apparent illness. Severe cases of EEE (involving encephalitis, an inflammation of the brain) begin with the sudden onset of headache, high fever, chills, and vomiting. The illness may then progress into disorientation, seizures, or coma. EEE is one of the most severe mosquito-transmitted diseases in the United States with approximately 33% mortality and significant brain damage in most survivors. There is no specific treatment for EEE; care is based on symptoms. You can reduce your risk of being infected with EEEV by using insect repellent, wearing protective clothing, and staying indoors while mosquitoes are most active

Life cycle

EEE is capable of infecting a wide range of animals including mammals, birds, reptiles and amphibians. The virus is maintained in nature through a bird - mosquito cycle. There are two mosquito species primarily involved in this portion of the cycle, they are Culiseta melanura and Cs. morsitans. These mosquitoes feed on the blood of birds. The amount of virus found in nature increases throughout the summer as more birds and more mosquitoes become infected. Transmission of EEEV to mammals occurs via other mosquitoes. These other mosquitoes are called bridge vectors because they bring the virus from avian populations to mammalian populations. They include Coquiletidia perturbans, Aedes vexans, Ochlerotatus sollicitans and Oc. canadensis. All these mosquitoes are primarily mammalian feeders. Generally, people only become sick through the bite of an infected mosquito. Humans, horses and other infected mammals do not circulate enough virus in their blood to infect additional mosquitoes. There have been some cases where EEEV has been contracted through lab exposures or from exposure of the eyes, lungs or skin wounds to brain or spinal cord matter from infected animals.

* the virus travels via lymphatics to lymph nodes and replicates in macrophages and neutrophils, resulting in lymphopenia, leukopenia and fever. Subsequent replication occur in other organs leading to viremia.
* Symptoms in horses occur 1–3 weeks after infection and begin with a fever that may reach as high as 106 °F (41 °C). The fever usually lasts for 24–48 hours.
* Nervous signs appear during the fever that include sensitivity to sound, periods of excitement, and restlessness. Brain lesions appear causing drowsiness, drooping ears, circling, aimless wandering, head pressing, inability to swallow, and abnormal gait. Paralysis follows causing the horse to have difficulty raising its head. The horse usually suffers complete paralysis and death 2–4 days after symptoms appear. Mortality rates among horses with the eastern strain range from 70 to 90%. In humans symptoms include high fever, muscle pain, altered mental status, headache, meningeal irritation, photophobia, and seizures, which occur 3–10 days after the bite of an infected mosquito.

Treatment

There is no cure for EEE. Treatment consists of corticosteroids, anticonvulsants, and supportive measures such as intravenous fluids, tracheal intubation, and antipyretics. Some 30-35% of infected humans die, and half of survivors are left with neurologic sequalae.

There is no cure for an EEE infected horse, and 75–90% of horses die. Survivors are left with severe sequalae.IV ribavirin has been considered as a possible treatment.