Eastern Equine Encephalitis (EEE) virus is a rare but severe and potentially fatal virus transmitted primarily by mosquitoes. EEE primarily affects horses, but humans can also contract it. Most cases in the United States occur in the gulf coast and eastern states. Humans with EEE can have a range of symptoms, from mild flu-like signs to severe neurological complications. For horses, EEE is more often fatal, with a mortality rate approaching 90% in untreated cases. The most common symptoms include fever, headache, and vomiting. However, in more severe cases, it can lead to encephalitis, a dangerous inflammation of the brain, which may cause seizures, coma, and even death. The fatality rate for EEE is high, ranging between 33% and 50% in severe cases. For untreated horses, EEE is often fatal, with a mortality rate approaching 90%.

EEE is an “arborvirus,” a group of viruses transmitted by mosquitos, ticks and other similar creatures. Mosquitos are the principle way EEE spreads. Wild birds that live in freshwater habitats are the most common hosts of the EEE virus but rarely become ill. Mosquitoes bite the birds and then transmit the virus to other animals or humans. The prevalence of the EEE virus is strongly linked to mosquito populations and their habitats. There are no vaccines for humans against EEE and other similar viruses spread by mosquitos. Instead, “we basically rely on vector control, monitoring mosquitoes, putting insecticide on and telling people not to go out after dusk and to wear Deet, but it’s not a perfect solution,” said Dr Arthur Reingold, epidemiology professor at the University of California, Berkeley School of Public Health.

In response to a recent EEE fatality in New Hampshire and two cases of EEE in Massachusetts, local officials have issued health warnings and, in one community, imposed restrictions on the use of public fields at night when the mosquitos are most active. These measures have been met with some surprisingly negative pushback. “In my family, we were completely done when Covid ended. We were done being locked inside, being scared. Living scared is no way to live,” said one local resident.

Mosquitos breed in standing water and warmer temperatures allow mosquitos to lay eggs more frequently. Climate change creates conditions that increase the mosquito population and thereby directly lead to increases in mosquito borne illness such as EEE. These include:

1. Temperature Increases: Warmer temperatures extend the range of mosquitoes. As average temperatures rise, mosquitoes survive and reproduce in areas previously too cold for them. This geographical expansion introduces EEE virus into new regions, increasing the risk of outbreaks in areas that were previously less affected.
2. Altered Rainfall Patterns: Climate change is also influencing rainfall patterns, leading to more intense and variable precipitation. Since mosquitoes need water to breed, increased rainfall creates more breeding sites, leading to higher mosquito populations and a greater risk of disease transmission.
3. Changing Ecosystems: Alterations in ecosystems due to climate change also impact the host animals and vectors involved in the transmission of EEE. Shifts in bird migration patterns or changes in habitat influence the dynamics of the virus’s transmission cycle. When migratory birds move to new areas due to changing climate conditions, they carry EEE virus to these regions.
4. Extreme Weather Events: More frequent and severe weather events, such as hurricanes and floods, also impact the spread of EEE. These events can lead to increased breeding sites for mosquitoes and disrupt control measures. For instance, after a flood, standing water can provide ideal conditions for mosquito larvae to thrive.

As the geographic range of mosquitoes expands and their populations increase, there is a higher likelihood of EEE virus spreading to new areas. This not only poses a risk to human health but also places additional burdens on public health systems and veterinary services.

Preventative measures become crucial in managing the risk of EEE. These include:

• Mosquito Control: Reducing mosquito breeding sites by eliminating standing water and using insecticides can help manage mosquito populations. Such integrated pest management strategies are effective mosquito populations controls.
• Vaccination: For horses, vaccination against EEE is a critical preventative measure. For humans, no specific vaccine for EEE is available, so prevention focuses on reducing mosquito exposure through the use of repellents, wearing protective clothing, and avoiding outdoor activities during peak mosquito activity times.
• Public Awareness: Educating the public about the risks of EEE and how to prevent mosquito bites is essential. Awareness campaigns can help people take proactive measures to protect themselves and their families.

As climate change continues, the spread of vector-borne diseases like EEE will undoubtedly increase. Recognizing this relationship between climate change and disease dynamics is crucial for developing effective strategies to mitigate these risks. Proactive steps include monitoring changes in mosquito populations, virus transmission patterns and the effectiveness of control measures.

The EEE virus serves as a dramatic example of how climate change can impact disease dynamics. The interplay between environmental changes and disease transmission highlights the need for a comprehensive approach to public health and vector control in the face of a changing climate. It also provides yet another reason for the implementation of urgent measures to reverse climate change.

For more insights on the impact of climate change on public health and other pressing issues, stay tuned to our blog for future updates and expert analyses.

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