Introduction

Eastern equine encephalitis (EEE) is a rare vector-borne viral disease that is transmitted to humans by mosquitoes. A common name for the disease is sleeping sickness, or it may also be referred to as Triple E, the abbreviation of Eastern equine encephalitis. As the name of the disease explains, EEE is an encephalitis, which basically means an infection of or autoimmune attack of the brain. The encephalitis caused by EEE results in an encephalopathy, which simply refers to any illness that is concerned with the brain.

EEE affects South, Central, and North America as well as the Caribbean. Despite this wide geographic distribution, EEE is mostly concentrated in or endemic to the Eastern and Gulf states of the USA and Southeastern Canada.¹ In the USA, there have been between 4 and 38 reported cases of EEE between 2011 and 2020.² This disease causes serious illness in humans and horses.

Encephalitis has implications for pregnant women and foetuses as well as newborn babies. As such, it is important to take precautions around EEE when it comes to pregnancy. Here we will discuss how EEE affects the human body, including how it could affect gestating women and newborns.

Unpacking EEE

Transmission

EEE is caused by an arthropod-borne virus (Arbovirus) of the family Togoviridae, genus Alphavirus. It is passed on to humans by mosquitoes. Amongst other Alphaviruses, the EEE virus is the one that causes the most severe form of illness. The virus is transmitted amongst birds of the order Passeriformes by the Culiseta melanura species of mosquitoes, which are believed to be the primary vector. However, Culiseta melanura mosquitoes do not typically feed on humans who are said to be dead-end hosts. Instead, the virus is transmitted from birds to humans by the Coquillettidia pertubans, Aedes solicitans, and Ochlerotatus canadensis species of mosquitoes which are referred to as the bridge vectors. Humans are referred to as dead-end vectors because the virus in humans cannot multiply such that mosquitoes cannot spread the virus to other organisms. Owing to its transmission, people who are more at risk of contracting the virus are those in swampy areas where the mosquito vector is present. The transmission of the virus by the mosquitoes occurs mostly during the summer, with no transmission in the winter when the mosquitoes are not feeding. The virus cannot be transmitted between people.^1,3

History of the EEE virus

The disease was first recorded in Massachusetts in the year 1831, however, the virus itself was first identified in 1831. In humans, infections with the virus were first recorded in 1938 whereby there were 34 cases, which resulted in 25 fatalities. This outbreak in humans occurred in Massachusetts. A subsequent outbreak occurred in 1959 in New Jersey with 32 recorded identified cases and a high fatality rate. The most recent outbreak in cases was in 2019 when 38 cases were reported.^2,3

There were two types of the virus according to their biochemical properties, the North American and South American types. A newer classification has, however, divided the virus into four lineages. Lineage 1 is specific to North America and the Caribbean. The other lineages are specific to Central and South America.² 

Clinical symptoms

The incubation period of the EEE virus is said to be between 4 and 10 days. At onset, the disease is signalled by non-specific symptoms such as fevers, chills, and joint pain. Some people go on to develop encephalitis and meningitis, which is an infection of the brain and meninges. The symptoms that go with the infection of the brain include fever, seizures, headaches, and changes in behaviour. Patients may even go on to be comatose. Even after surviving the disease, patients may remain with impairments such as seizures and paralysis.²

Potential risks of EEE in pregnancy

Due to the rarity of the disease, there is a lack of information regarding EEE in pregnant women. However, other related alphavirus diseases also cause encephalitis, namely Venezuelan equine encephalitis (VEE) and Western equine encephalitis (WEE).⁴ Other mosquito-transmitted viruses that may also cause encephalitis are the Zika and Dengue viruses.^5–7 Drawing from what is known about VEE and WEE, these are some of the effects of viral encephalitis in pregnancy:

• Damage to the placenta
• Death of the foetus
• Miscarriages and stillbirths
• The virus may also be passed onto the foetus 
• The newborn can also suffer from serious congenital defects

Diagnosis of EEE

To diagnose Eastern equine encephalitis, several serological tests are conducted. Blood and cerebrospinal fluid (CSF) samples of patients are analysed for the presence of the virus using techniques such as the polymerase chain reaction (PCR). Encephalitis may also be detected using imaging technology such as MRI and CT scans.²

Treatment and prevention of EEE

There are currently no available drugs used to treat EEE. Patients are placed under supportive care and treated for whatever symptoms they may be exhibiting. No vaccine has been approved for use in humans to prevent the disease.²

To prevent contracting EEE, precautions need to be taken by people in endemic areas. These include measures to prevent contact with mosquitoes. Preventative measures may include using insecticides, mosquito nets and clothing that may prevent mosquito bites.

Prognosis

The prognosis for this disease is poor as there is no available pharmaceutical treatment. Many people with the disease may develop neurological defects such as seizures or go into a coma. The fatality rate of the disease stands at between 30% and 70%.²

FAQs

What complications can arise from having Eastern equine encephalitis?

People with Eastern equine encephalitis can develop severe illnesses such as seizures and may even be paralysed.

What can you do to prevent getting Eastern equine encephalitis?

No vaccine has been approved to prevent illness in humans. The best way to prevent illness is to prevent contact with mosquitoes in infested areas.

Which geographic region is most affected by Eastern equine encephalitis?

The Eastern states of the USA are the most affected by Eastern equine encephalitis.

What is an alternative name for Eastern equine encephalitis?

Eastern equine encephalitis is also referred to as sleeping sickness or Triple E.

How does Eastern equine encephalitis spread?

Eastern equine encephalitis is transmitted from passerine birds to humans and horses by mosquitoes.

Can people be cured of Eastern equine encephalitis?

There are currently no pharmaceutical drugs for the treatment of Eastern equine encephalitis. Patients of Eastern equine encephalitis are placed under supportive care. 

Summary

EEE is a very rare viral disease that is prevalent in the Eastern states of the USA. It is caused by a virus that is passed on from birds to humans by mosquitoes that inhabit swampy forest areas. In some patients, it may result in encephalitis whereby the brains of patients are infected by the virus. There seems to be no available data regarding EEE in pregnancy but there are other related viruses for which there is pregnancy information. The risks of viral encephalitis in pregnancy include stillbirths and miscarriages. The virus may also affect the newborn, resulting in serious congenital ailments. At present, no drugs have been approved for the treatment of EEE and there is also no effective vaccine. Patients of EEE are placed under supportive care.