Mosquito-Borne Diseases: EEE Vs West Nile Virus

  • Priyanka Thakur Bachelor in Medicine, Bachelor in Surgery (MBBS), DRPGMC, India

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What are viruses? You might have known them through the recent COVID-19 pandemic, but there is actually so much more to it. Viruses invade different animal hosts to replicate themselves and then release their particles to other hosts to further spread the infection. Eastern Equine Encephalitis virus and West Nile virus are one of the many viruses out there and this article will explore the different aspects of these viral diseases. 

Introduction to viruses 

Viruses are infectious and obligate intracellular parasites, meaning they cannot survive on their own and rely on a host to replicate their viral particles. They are generally small in size, ranging from 20 to 200 nm in diameter.1 These parasitic pathogens consist of genetic material (either DNA or RNA) and capsid, a protein coat that protects the insides. There are currently around 1031 viruses on Earth,2 and most of them don't actually affect humans, but they each play a role in regulating the various ecosystems worldwide.

Transmission of viruses

The modes of transmission of viral diseases can be categorised into direct and indirect.3 In direct transmission, the infection is passed on directly from one host to another, through airborne droplets and aerosols or sexually through bodily fluids. On the other hand, indirect transmission involves the presence of an intermediate contact, including:

  • Formite-borne - objects contaminated with an infectious agent 
  • Vector-borne - another animal is the carrier of the pathogen 
  • Waterborne - spreading of pathogens through contaminated water
  • Foodborne - food is handled by an infected person or has been contaminated during the production 

In this article, mosquito-borne viral diseases will be the main point of focus, which is part of vector-borne transmissions. The virus infects a mosquito and replicates inside it, which the infected mosquito can then bite a human and the virus will be transmitted into a new host through the saliva.4 

Eastern equine encephalitis virus

The Eastern Equine Encephalitis (EEE) virus is a rare virus that is transmitted on the eastern coast of North America and the Caribbean. This virus was first discovered in an encephalitis outbreak among a horse population in 1933 and was found in humans by 1938. 

In the majority of cases, infected people do not show any symptoms,5 but in more severe cases, the symptoms can include:

These symptoms vary for each person, depending on their age and underlying diseases, and it usually takes from 4 to 10 days for symptoms to develop. Around 30% of the patients die due to the severity of the infection, while the remaining survivors have permanent neurological damage. 

EEE virus can be spread to humans through infected mosquito species, such as Aedes, Coquillettidia and Culex, and it is important to note that this dangerous viral disease does not transmit between people. 

The diagnosis of the EEE virus involves blood and spinal fluid tests to detect the presence of the virus itself or the antibodies against it. Clinicians will also evaluate the potential symptoms of the patient and assess the travel history and potential encounters with infected mosquitoes. 

Unfortunately, there are currently no medications to treat this viral disease or any preventional vaccinations,6 so it is crucial to be aware of the potential risks and precautions required.

West nile virus

West Nile virus is one of the more common mosquito-borne diseases, distributed in countries in Europe and the United States, where the major bird migratory routes are located. This virus was first encountered in 1937, in Uganda's West Nile district, where a woman was infected with a fever. 

Most patients with West Nile virus do not develop any symptoms,7 but potential mild symptoms include:

These usually last for a week and will recover completely, fatigue and tiredness brought about by the virus can last up to months. In more serious cases, the virus will infect the central nervous system, leading to:

Thankfully, the fatality of the West Nile virus is much lower than the EEE virus, where 1 in 10 people who develop into a severe case dies. 

The main mode of transmission of the virus is through mosquitoes, especially from the Culex genus. When humans are bitten by these infected mosquitoes, they will acquire the virus. Some cases can be caused by blood transfusion and organ transplantation, where the donors have visited places prevalent with West Nile viruses. 

Similar to the EEE virus, suspected people can be diagnosed by carrying out laboratory tests of their blood and spinal fluids and an evaluation of the travel history and symptoms is needed. There are also no treatments or vaccinations for the infections. There are only medications to alleviate symptoms and resting will allow the patient to recover within a week. Moreover, most people who have already been infected by the West Nile virus have been shown to have developed immunity to it. 

Precautions and awareness

Despite most cases of EEE and West Nile viruses being asymptomatic or having mild symptoms, it is vital to raise awareness of these viruses due to their potential life-threatening consequences. 

There are several prevention strategies to adopt to protect ourselves from these mosquitoes: 

  • Using insect repellent with the appropriate ingredients and methods of application, according to the government advice 
  • Wearing permethrin-treated long sleeves and trousers 
  • Avoiding exposure to mosquitoes - using insect mesh on windows, air conditioning, sleeping under mosquito nets 

By taking these measures, we can prevent being bitten by infected mosquitoes and protect ourselves from the virus. 

Research and development 

Although there are no commercially available vaccinations for the public, there has been research into potential treatments. This includes a ChimeriVax-WNV, which is a live attenuated vaccine targeting the West Nile Virus,8,9 that is undergoing clinical trials to determine its safety and efficacy. As for the EEE virus, there have been clinical trials to investigate and develop a vaccination,10 which have shown success and appear to be safe for human use. However, it is not available for public use and remains under research due to the limited resources and high cost of production. 


Eastern Equine Encephalitis virus and West Nile virus share many similarities, from their symptoms to diagnosis to transmission. However, one stark difference is the fatality rates, the consequences of the West Nile virus are much milder than the EEE virus. Nevertheless, it should not be something we overlook, as both viruses have the potential to lead to deadly consequences. There are several preventive actions to take to reduce the chances of getting bitten by mosquitoes and people who are travelling to countries that are widespread by the EEE virus and West Nile virus need to be cautious.


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  • Mushegian AR. Are There 1031 Virus Particles on Earth, or More, or Fewer? J Bacteriol. 2020; 202(9):e00052-20.
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  • Habarugira G, Suen WW, Hobson-Peters J, Hall RA, Bielefeldt-Ohmann H. West Nile Virus: An Update on Pathobiology, Epidemiology, Diagnostics, Control and “One Health” Implications. Pathogens [Internet]. 2020 [cited 2024 Feb 8]; 9(7):589. Available from:
  • Pierson BC, Cardile AP, Okwesili AC, Downs IL, Reisler RB, Boudreau EF, et al. Safety and immunogenicity of an inactivated eastern equine encephalitis virus vaccine. Vaccine [Internet]. 2021 [cited 2024 Feb 8]; 39(20):2780–90. Available from:

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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