Brain-infecting virus has spread across the US at record rates this year

By Sally Robertson, B.Sc.Reviewed by Kate Anderton, B.Sc. (Editor)Sep 24 2019

Health officials have announced over the weekend that more people have been infected with or died from the Eastern Equine Encephalitis (EEE) virus, making 2019 the worst year yet for recorded cases.

Negro Elkha | Shutterstock

Last Friday, officials announced the death of a man in Massachusetts, which is the second death and tenth case of a person infected with the virus in the state this year. On the same day, an eighth case was recorded in Michigan, where three deaths have also been linked to the virus.

Two more cases have been reported in New Jersey, where a person also died from the infection in August and, in Connecticut, the first death and second case of infection has been reported.

So far this year, more than 25 confirmed or suspected cases of EEE have been reported across six states and there have been at least seven deaths.

The Centers for Disease Control and Prevention (CDC) says the country typically sees an average of seven severe cases per year and that 2019 has been one of the worst years for recorded cases in decades.

What is EEE?

EEE is an arbovirus. This family also contains the West Nile virus and is spread by mosquitoes or other arthropods. It is one of several New World encephalitis viruses and it is found in the northeast of the country, as well as along the Gulf Coast and the Great Lakes. Sometimes cases occur in Canada and at least one case was reported in Ontario in 2016.

According to Marc Fischer, a medical epidemiologist from the CDC, some people only develop mild, flu-like symptoms, but around one-fifth develop clinical illness and about half of those develop neuroinvasive disease, where the virus infects and inflames the brain.

This can cause encephalitis, which may begin with fever, chills, headache, and vomiting and then go on to cause disorientation and seizures. The mortality rate is high, with the illness killing about one-third of those who develop encephalitis.

“It is the highest case fatality of all of the arboviruses that occur in the United States,” Fischer said. Those who survive often suffer from long-term side effects including mild-to-severe brain damage.

Why 2019 is looking like such a worrying year

According to Theodore Andreadis, head of the Center for Vector Biology & Zoonotic Diseases in Connecticut, it is not just a large number of human cases and deaths linked to EEE that are making 2019 such a worrying year. The problem is also how far the virus seems to have spread in people and birds across the eastern half of the country.

Periodically, you know, you might get an outbreak in Massachusetts, Rhode Island, and not necessarily see it in Connecticut and New Jersey. But this year, it’s really all over the entire region. And we don’t even know how many other people might have developed mild sickness or been exposed to the virus and not developed any symptoms. So it’s really rather extraordinary this season.”

Theodore Andreadis, Center for Vector Biology & Zoonotic Diseases

Andreadis and other experts have observed that the virus has recently moved into regions where it has rarely or never been seen before, including as far north as Canada. Furthermore, certain strains of the virus are surviving for longer.

Climate change is part of the problem

Andreadis says that although climate change is not the only reason this is happening, it is definitely playing a role.

The impact that a changing climate has on weather conditions certainly has an impact on mosquito populations, he says. For example, milder winters mean that mosquito populations in the North of the country can survive the season and then spread more EEE in the wild the following year.

Warmer summers also tend to boost the mosquitoes’ populations and feeding activity, which increases the risk of transmission.

Furthermore, the increasing frequency of extreme weather events, particularly heavy flooding, also results in more breeding grounds for mosquitoes carrying the virus and a greater likelihood of it being spread to people living in nearby swampy areas.

In the long term, it is almost certain that climate change will mean EEE and other insect-borne diseases such as West Nile and Lyme become a more common threat to people in the US.

Worryingly, the tools available to combat them are not exactly effective, meaning it is essential that researchers and authorities continue to monitor the spread of such diseases.

Warning to campers and hunters in swampy areas

As for people living in the areas where EEE could strike at any moment, it is important that they stay vigilant – at least until the first winter frost arrives.

Mosquito numbers are going down. The virus activity is also going down, but it’s still there in some areas."

Theodore Andreadis

This ongoing risk is particularly relevant to individuals who are keen to camp or hunt near swampy areas at dusk or dawn. Andreadis advises that the best way for those people to protect themselves is to hold off for a couple more weeks, and barring that, to wear mosquito repellent at all times.