First US Death from Rare Mosquito-Borne Virus Reported in New Hampshire

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New Hampshire, August 29, 2024 — The United States has recorded its first death from eastern equine encephalitis virus (EEEV) this year, a rare but severe mosquito-borne virus. Health officials in New Hampshire confirmed the death on Tuesday, marking the state’s first human case in a decade and the fifth case reported in the US this year.

The patient’s death has heightened concerns across the region, with surrounding areas, particularly in Massachusetts, on high alert due to the detection of the virus in local mosquito populations.

What is EEEV?

Eastern equine encephalitis virus, often referred to as “Triple E,” was first identified in horses in Massachusetts in 1938. It is a rare virus that primarily attacks the central nervous system in humans, causing inflammation or swelling of the brain, which can lead to severe neurological complications.

While the virus is rare, it is highly deadly, with a mortality rate of approximately 30% in those infected. Symptoms typically appear four to 10 days after being bitten by an infected mosquito and include sudden onset of fever, chills, headaches, vomiting, and, in severe cases, seizures and disorientation.

Where is the Virus Found?

The virus is primarily found in North America and the Caribbean, with human cases most commonly occurring in the eastern and Gulf Coast states of the US. The spread of EEEV is closely linked to the ecology of various bird species and mosquito populations that thrive in arboreal swamps.

The black-tailed mosquito (Culiseta melanura) is the primary carrier of EEEV, although other mosquito species, such as Aedes, known for transmitting dengue, and Coquillettidia, have also been identified as carriers.

How Does the Virus Spread?

The virus circulates in bird populations in hardwood swamps. Mosquitoes that feed on both birds and mammals can spread the virus when they bite an infected bird and then transmit the virus to humans or horses. Unlike birds, humans and horses are considered “dead-end hosts,” meaning they cannot spread the virus further.

Current Situation in the US

As of 2024, there have been five confirmed human cases of EEEV in the United States, with cases reported in Massachusetts, New Jersey, Vermont, Wisconsin, and New Hampshire. The only death so far has occurred in New Hampshire.

Public health officials have emphasized the severity of the situation, urging residents to take preventive measures as the peak mosquito season continues through the summer and into the autumn.

Preventive Measures and Response

With no specific treatment or vaccine available for EEEV, prevention remains the most effective defense. Public health authorities recommend applying government-approved insect repellents, wearing protective clothing during peak mosquito activity times (dusk to dawn), installing screens on windows and doors, and eliminating standing water where mosquitoes breed.

In response to the outbreak, several states, including Massachusetts, have implemented mosquito control programs that involve aerial and truck-mounted spraying of insecticides. Additionally, towns such as Plymouth, Massachusetts, have closed public outdoor facilities from dusk to dawn to minimize the risk of exposure.

Link to Climate Change

Experts have raised concerns that climate change may be contributing to the extended duration of mosquito seasons, thereby increasing the risk of virus transmission. Warmer temperatures and higher humidity levels create favorable conditions for larger mosquito populations, which may in turn lead to more human and horse cases of EEEV.

Despite the severity of EEEV, other mosquito-borne illnesses, such as West Nile virus and dengue fever, continue to affect the US, with significant numbers of cases reported each year. However, EEEV’s high mortality rate and impact on the brain make it a particularly alarming public health concern.

As the situation unfolds, health officials are closely monitoring the spread of the virus and urging the public to remain vigilant in protecting themselves from mosquito bites.

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