What is the deadly ‘Triple E’ mosquito virus spreading in the northeastern United States? | Health News
The United States recorded its first death this year from a rare mosquito-borne virus.
New Hampshire officials announced the patient’s death Tuesday, marking the state’s first human case in a decade and the fifth U.S. case of the virus this year.
Mosquitoes in several areas of the state are believed to be infected with the virus while surrounding areas are on high alert, particularly in neighboring Massachusetts.
What is the virus transmitted by mosquitoes and how far can it spread?
What is the virus?
The virus is officially called Eastern equine encephalitis virus (EEEV), also known as “Triple E.” Rare but serious, it was first identified in horses in Massachusetts in 1938.
Since then, there have been 118 human cases and 64 deaths from the virus in the state, according to data from the Massachusetts Department of Public Health.
In humans, the virus attacks the central nervous system and can cause inflammation or swelling of the brain.
Where is the virus found?
The virus is present in North America and the Caribbean, while human cases occur primarily in the eastern and Gulf Coast states of the United States.
This can be attributed to a “complex ecology of several different bird and mosquito species that rely on tree marshes for breeding,” said Verity Hill, a research associate at Yale University’s School of Public Health.
Additionally, the black-tailed mosquito – the primary vector of the virus – is found primarily in the eastern United States, Mexico and the Caribbean.
How does the virus spread?
The virus typically circulates among birds living in deciduous swamps. Mosquito species that feed on both humans and mammals spread the virus when they bite an infected bird and then a mammal and inject the virus into its bloodstream.
Unlike birds, infected humans and horses are “dead-end hosts,” meaning they don’t have enough virus in their blood to transmit EEEV to a mosquito that might bite them, Hill told Al Jazeera. This means they can’t transmit the virus to other animals or humans.
Infections tend to be asymptomatic in birds, but fatal in horses.
The most common vector of EEE is the black-tailed mosquito (Culiseta melanura), while other vectors include Aedes, which transmits dengue virus, and Coquillettidia.
Summer and fall are mosquito season in the United States, making it a particularly risky time for these viruses.
What are the symptoms?
Symptoms in humans usually appear four to ten days after infection. These include:
- Sudden onset of fever and chills
- Headache
- Vomiting and diarrhea
- Crises and behavioral changes
- Drowsiness and disorientation
- In severe cases, swelling of the brain (encephalitis)
EEE is diagnosed by looking at symptoms and testing spinal fluid or blood, which can show whether the virus or viral antibodies are present.
How many cases of the encephalitis virus are there this year?
In 2024, there were five confirmed human cases of EEEV in the United States: one each in Massachusetts, New Jersey, Vermont, Wisconsin, and New Hampshire.
In Oxford, Massachusetts, an 80-year-old man was infected in mid-August, becoming the first human case in the state since 2020.
The only death reported so far is from New Hampshire.
How common and dangerous is the virus?
EEE is rare in humans. Between 2003 and 2023, there were 196 cases in the United States, according to data collected by the Centers for Disease Control and Prevention (CDC).
The country records an average of 11 cases per year. The largest outbreak occurred in 2019 with 38 cases and 12 deaths nationwide.
Public health authorities consider it a serious disease because of its impact on the brain and its 30% mortality rate.
Even if they survive, many infected people suffer long-term neurological problems.
How can the virus be controlled or treated?
Public health authorities have said prevention is crucial because there is no specific treatment or vaccine for humans. Control measures include:
- Application of government-approved insect repellents
- Implementation of mosquito control programs, including aerial and truck spraying of pesticides
- Wear long sleeves and pants during peak mosquito hours (dusk to dawn)
- Installation of anti-mosquito screens on windows and doors
- Drainage of stagnant water around homes
- Avoid outdoor activities during peak mosquito periods
Treatment focuses on managing symptoms and providing supportive care, such as prescribing pain medication.
Mosquito and tick bites can cause serious diseases like EEE and Lyme disease. When outdoors, use an EPA-approved repellent, applied slowly and evenly to your face, neck, arms, and legs. Wear full protective clothing whenever possible. More information: https://t.co/DD6BYzyvj2. pic.twitter.com/84eMaxr1Kg
— Massachusetts Public Health (@MassDPH) August 25, 2024
What measures are the authorities taking?
States are taking several measures to slow the spread of the virus, including varying levels of lockdown.
The city of Plymouth, Massachusetts, has decided to close outdoor public facilities from dusk to dawn. The northeastern US state has also urged residents to avoid outdoor activities during those peak hours when mosquitoes are abundant.
Aerial and overhead spraying of insecticides is also being carried out in several areas.
What other viruses or diseases are transmitted by mosquitoes in North America?
West Nile virus, transmitted by mosquitoes but less deadly, has infected 289 people in the United States this year.
The country has also recorded 3,861 cases of dengue fever this year, already surpassing the 3,352 cases reported in the whole of 2023.
Dengue fever causes high fevers and muscle and joint pain and is reaching record levels worldwide, according to the CDC. The mortality rate can be as high as 13% in untreated patients.
Is climate change causing the spread of this virus?
Experts warn that climate change is extending the length of the mosquito season, which is characterized by high humidity and high temperatures.
The prevalence of the virus in mosquitoes may also be an indicator of risk to humans.
“Years with large populations of infected mosquitoes tend to have more human/equestrian cases,” Hill said, adding that climate change could favor larger populations of mosquitoes that can carry EEEV but would not introduce more virus.
This year’s cases are likely part of the normal dynamics of the virus, she said.
