The Silent Spread: Emergence of Eastern Equine Encephalitis

Authored By: Castine Hardesty

Art By: Amy Em

While a mosquito bite is nothing more than a small, itchy annoyance for most people, in many  tropical regions around the world, one bite can have devastating consequences, including death. As the Earth gets progressively warmer each year, the threat of mosquito-borne diseases has started to become actualized in historically cooler areas of the globe, including the Northeast US. Climate change is increasingly opening up a new niche in the Northern Hemisphere for mosquitoes to inhabit, bringing with them viruses such as the Zika virus, West Nile virus, and, more recently, Eastern Equine Encephalitis (EEE), which has a sobering 30% fatality rate [1]. Although still considered a rare disease, the implications of climate change’s effects on an increase in EEE virus cases are catastrophic.

Eastern Equine Encephalitis virus is a mosquito-borne disease that originates from North American and Caribbean freshwater swamps. Mosquitoes, including those that carry the EEE virus, rely on warm temperatures to survive. In the northeast, mosquitoes are typically killed by frost. However, every year, this phenomenon occurs later in the year, increasing the length of mosquito seasons. Studies have predicted that by 2050, the mosquito season will be twice as long, increasing the opportunity for transmission of deadly mosquito-borne diseases like EEE, for which there is no vaccine [1, 2]. Instead, doctors are forced to simply treat the symptoms; as EEE commonly causes encephalitis or brain swelling in humans, one conventional procedure used is a craniotomy to relieve pressure against the skull [3].

The EEE virus is naturally found in bird reservoirs that inhabit swamp ecosystems, but can be transmitted to humans and horses through mosquitoes that feed on both birds and animals. An EEE infection puts individuals at risk for developing encephalitis. Significantly, even those individuals who survive EEE are at a high risk for suffering from long-term neurological problems such as seizures and intellectual and behavioral impairment [2, 3]. Although an EEE infection is still rare in the United States, there is a concerning uptick in the number of diagnosed cases in recent years. In 2024, there were a total of 19 reported cases of EEE, with the majority of these cases across New England and New York, compared to only one reported case in 2022, and seven reported cases in 2023 [4]. 

Although climate change is raising the temperature of the Earth at increasingly rapid rates, mosquito-borne diseases like EEE are not new to the United States [5]. In fact, in the 18th and 19th centuries, mosquito-caused yellow fever epidemics, which caused over 100,000 U.S. deaths alone, were common in cities as far north as Boston, Massachusetts, and Providence, Rhode Island before being considered virtually eradicated after multiple eradication efforts [6]. However, rising temperatures and frequent natural disasters leading to floods with standing water, due to climate change, risks creating the perfect environment for mosquitoes to breed, multiply, and spread diseases, as shown in Pakistan, where severe flooding caused a fivefold increase in malaria cases across the country [7]. The devastating impacts of yellow fever epidemics in the past warn that the emergence and rise of Eastern Equine Encephalitis in the United States should not be taken lightly.

It’s not too late to combat the rise of mosquito-borne diseases in the United States. Because there is no vaccine currently available for EEE virus, it is imperative to take proper precautions against this disease and others. Simple yet effective measures, like emptying standing water in living areas, wearing insect repellent, and using screens on doors and windows are all ways to stay protected from this virus [3]. Personal protection, however, is not enough - community-level intervention is essential to effectively decrease mosquito populations. While these methods may be successful in decreasing mosquito-borne diseases in human populations, it is clear that climate change is only increasing the prevalence of mosquito-borne illnesses, leading us to the dilemma of how to combat the increase in mosquito season length in the US. Several proven approaches such as releasing sterile mosquitoes, spraying insecticides, and using the bacterium Wolbachia, a genus of gram-negative bacteria that infects female mosquitoes and inhibits transmission of diseases to humans, have been used in regions such as Sub-Saharan Africa, Southeast Asia, and Latin America, where mosquito-borne diseases such as dengue fever, chikungunya, and zika virus are endemic [8]. These sustainable and effective solutions could theoretically be applied in the United States to mitigate the devastating effects of mosquito-borne disease in populations. The issue of climate change, however, must also be addressed through the actions and advocating of the masses. Without the voices of the people supporting greater climate change policies, a reverse of trend when it comes to Eastern Equine Encephalitis cannot be expected.    

References

1.  Powell, A. (2024, October 16). Threat of mosquito-borne diseases rises with global temperature. Harvard Gazette. https://news.harvard.edu/gazette/story/2024/10/threat-of-mosquito-borne-diseases-rises-with-global-temperature/ 

2. Centers for Disease Control and Prevention. (2024, May 15). Eastern equine encephalitis: Causes and how it spreads. Centers for Disease Control and Prevention. https://www.cdc.gov/eastern-equine-encephalitis/cause-and-spread/index.html 

3. “Eastern Equine Encephalitis (EEE): Causes & Symptoms.” Cleveland Clinic, 27 Sept. 2019, my.clevelandclinic.org/health/diseases/21187-eastern-equine-encephalitis-eee.

4. Centers for Disease Control and Prevention. (2025, January 14). Current year data (2024). Centers for Disease Control and Prevention. 

5. McGrath, M., & Poynting, M. (2023, November 18). Climate change: Is the world warming faster than expected?. BBC News. https://www.bbc.com/news/science-environment-67360929 

 6. Moreno-Madrinan, M. J., & Turell, M. (2018, May). History of mosquito-borne diseases in the United States and implications for new pathogens. Centers for Disease Control and Prevention. https://wwwnc.cdc.gov/eid/article/24/5/17-1609_article#r4 

 7. Phillips, M. (2025, January 15). The changing climate of vector-borne diseases. ContagionLive. https://www.contagionlive.com/view/the-changing-climate-of-vector-borne-diseases?rand=2671 

 8. Jackson, A. Explainer: How climate change is amplifying mosquito-borne diseases. World Mosquito Program. https://www.worldmosquitoprogram.org/en/news-stories/stories/explainer-how-climate-change-amplifying-mosquito-borne-diseases