Eastern Equine Encephalitis

Understanding Eastern Equine Encephalitis and Its Impact on Wildlife

Eastern Equine Encephalitis (EEE) is a viral disease that affects a range of animal species, including wildlife. EEE is a significant threat to wildlife populations and has caused numerous fatalities in both domestic and wild animals. This article aims to provide an overview of EEE, its causes, significance, species affected, distribution, transmission, clinical signs, diagnosis, treatment, and management strategies to help scientists and academics better understand and mitigate the impact of this disease on wildlife.


Eastern Equine Encephalitis is caused by a virus of the Togaviridae family, Alphavirus genus, transmitted by infected mosquitoes. The virus is primarily found in North, Central, and South America, and the Caribbean. The disease is often referred to as “triple E” or “sleeping sickness” and is considered a zoonotic disease, meaning it can be transmitted from animals to humans.


The EEE virus is a significant public health concern due to its high fatality rate and the potential for severe neurological disease in both humans and animals. In addition to the risk to human health, EEE has a significant impact on wildlife populations, particularly birds and horses. EEE can cause massive die-offs in bird populations, which can have cascading effects on ecosystems. Horses are particularly susceptible to the virus and can experience high mortality rates if not treated promptly.

Species Affected

The EEE virus has a wide range of host species, including birds, horses, humans, and other mammals. In birds, EEE can cause severe neurological symptoms, leading to death. Horses are particularly vulnerable to the virus with mortality rates above 30% being common. In humans, the virus can cause severe neurological disease, leading to permanent brain damage or death.


The EEE virus is primarily found in North, Central, and South America, and the Caribbean. In the United States, the virus is most prevalent in the eastern and southeastern regions, particularly in coastal areas. The virus is seasonal, with peak transmission occurring during the summer and fall months.


The EEE virus is primarily transmitted by mosquitoes. Mosquitoes become infected with the virus when they feed on infected birds. The virus then replicates within the mosquito, and the mosquito can transmit the virus to other animals or humans through its bite. The virus can also be transmitted from infected animals to humans through direct contact with infected tissue or bodily fluids.

Clinical Signs

Eastern equine encephalitis (EEE) can cause severe neurological symptoms in both humans and animals. Clinical signs of EEE in wildlife can be difficult to observe, as infected animals may exhibit only mild or no symptoms. However, in some cases, wildlife infected with EEE may show symptoms such as depression, ataxia, circling, head pressing, blindness, seizures, and ultimately, death.

Birds are particularly susceptible to EEE and may exhibit symptoms such as anorexia, lethargy, neurological signs, and death. Other wildlife species, including deer and rodents, may also be infected with the virus but often show few or no clinical signs.

It is important to note that EEE can also be transmitted to domestic animals, including horses, which can suffer severe and often fatal neurological symptoms. Clinical signs of EEE in horses can include fever, anorexia, depression, stumbling, weakness, and seizures.

Early detection and surveillance are key to controlling the spread of EEE in wildlife and domestic animals. If any wildlife is observed exhibiting symptoms of EEE, it is important to report it to the appropriate authorities immediately to prevent the virus from spreading further.

Vaccination is an effective way to protect domestic animals, including horses, from EEE. Insect control measures, such as the use of insecticides and the removal of standing water to prevent mosquito breeding, can also help reduce the risk of transmission.

In cases where EEE is suspected, infected animals should be isolated and treated symptomatically. There is currently no specific treatment for EEE, but supportive care can help manage symptoms and increase the chances of survival.

Overall, effective management of EEE in wildlife and domestic animals requires a combination of surveillance, vaccination, insect control, and supportive care.


Diagnosis of EEE in wildlife is typically done through laboratory testing of blood or tissue samples. In horses and humans, diagnosis is based on clinical signs, laboratory testing, and medical history.


There is no specific treatment for EEE in wildlife. Supportive care, including fluid therapy and anti-inflammatory medications, may be given to animals to help manage symptoms. In horses and humans, treatment is primarily supportive care and management of symptoms. There is no known cure for EEE.


Management of eastern equine encephalitis in wildlife is primarily focused on prevention and surveillance. Preventative measures include mosquito control programs and vaccination of domestic animals. Mosquito control can be achieved through environmental modification and use of insecticides, while vaccination of domestic animals such as horses can reduce the risk of infection in these animals and limit the spread of the virus to other animals and humans.

Surveillance is also a critical component of management, and involves monitoring the incidence and spread of the virus in wildlife populations. This can be achieved through various methods, including serological testing, viral isolation, and PCR testing. Wildlife managers can use this information to identify areas with high risk of infection and implement control measures to prevent further spread.

In the event of an outbreak, measures may be taken to reduce the risk of infection in humans and domestic animals, such as issuing warnings or advisories to avoid affected areas. Additionally, wildlife managers may consider reducing the population of mosquito vectors in affected areas through targeted insecticide application or other measures.

Overall, management of eastern equine encephalitis in wildlife requires a coordinated and multidisciplinary approach involving wildlife managers, public health officials, and veterinary professionals to prevent and control the spread of the virus.


Eastern equine encephalitis is a serious disease that can have devastating effects on both wildlife and humans. Its complex transmission cycle and wide range of susceptible species make it a challenging disease to control. Wildlife managers and researchers play an important role in monitoring and controlling the spread of EEE by understanding its ecology and transmission dynamics. Collaborative efforts between public health officials, wildlife managers, and veterinary professionals are essential for preventing and managing outbreaks of EEE and protecting public health.


  • Centers for Disease Control and Prevention. (2021, August 19). Eastern Equine Encephalitis (EEE). Retrieved from https://www.cdc.gov/easternequineencephalitis/index.html
  • Doherty, R. L. (1979). Arboviruses in the Australian region. Australian and New Zealand journal of medicine, 9(3), 296-301.
  • Hayes, E. B. (2009). Eastern equine encephalitis. New England Journal of Medicine, 360(19), 2024-2032.
  • McLean, R. G., Ubico, S. R., Bourne, D., Komar, N., & West Nile Virus Avian Mortality Surveillance Group. (2002). West Nile virus in livestock and wildlife. Current topics in microbiology and immunology, 267, 271-308.

Further Reading

  • Higgs, S., & Vanlandingham, D. L. (2015). The role of the mosquito in transmission of viruses. In Advances in insect physiology (Vol. 48, pp. 223-266). Academic Press.
  • Reisen, W. K. (2010). Landscape epidemiology of vector-borne diseases. Annual review of entomology, 55, 461-483.
  • Weaver, S. C. (2013). Urbanization and geographic expansion of zoonotic arboviral diseases: mechanisms and potential strategies for prevention. Trends in microbiology, 21(8), 360-363.
  • Sarcocystosis in Wildlife: Causes, Significance, and Management https://northeastwildlife.org/disease/sarcocystosis/