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An intense EEE cycle is in full swing in Mass. Here are some little-known facts on the virus.

This year marks the beginning of a new, intense cycle of the mosquito-borne illness that will likely persist for two to three years. The threat of infection, which has increased steadily over the last month, will last until the state sees several nights of prolonged hard frost.

Before August, Massachusetts hadn’t seen an active human case of EEE, or Eastern equine encephalitis, since 2013. Since then, five people and nine animals have been infected with the rare, but serious virus. A woman from Fairhaven has died. School and state officials are scrambling to reschedule nighttime activities in hopes of avoiding peak hours of mosquito activity and the threat of contracting the nightmarish virus, which is often deadly and leaves survivors with severe psychological and physical impairments.

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Here’s a rundown of some little-known facts on EEE.

1. It is extremely rare, but not worth the risk.

Even during an intense cycle, EEE infection in humans is extremely rare. Just 29 people in Massachusetts have been diagnosed with the disease since 2004, according to the Centers for Disease Control and Prevention. From 2009 to 2018, Massachusetts logged 10 cases of EEE, trailing Florida by three cases for the most in the nation, according to the CDC. Since the virus was first identified in Massachusetts in 1938, fewer than 100 cases have occurred.

The odds are roughly one in 3.1 million, putting it in the extremely rare, but best-avoided disaster category occupied by shark bites and lightning strikes. Of course, a person’s odds of contracting the virus increase quite a bit if they wander from dusk to dawn near a freshwater hardwood swamp in a critical risk zone while in the nude. Because of the potential ramifications of an EEE infection -- death is likely and psychological and physical impairments near certain in those who survive -- the health department and town officials wisely aim to limit the already small chance of infection.

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2. There is no vaccination. And its rarity is to blame.

This year stands to be one of the worst years for EEE in Massachusetts in the last two decades, yet still, only five people out of the nearly 7 million living in the state have been infected.

“Even though this year is an awful, awful year. You would have to vaccinate a very large population for what’s ordinarily just one or two cases a summer,” said Asim Ahmed, a leading expert on the virus and infectious disease doctor at Boston Children’s Hospital. “That as a public health calculus is a difficult thing for a vaccine manufacturer to undertake. It is very difficult to convince a drug company to pour all that money into preventing -- and it sounds horrid-- but potentially five awful cases. That’s a lot of expense for them.”

Even if a company were to pursue a vaccination, it would be hard to test the efficacy of a vaccine since so few people are infected each year. Ahmed compared the virus to the flu, which is widespread, and therefore easily tested.

“You can see what the effect of a good or bad vaccine is in large numbers, but when you look in very small numbers you potentially won’t see a difference,” he cautioned.

3. The virus “hijacks” a person’s immune system.

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Despite the colorful language, the explanation behind this process is chock full of science jargon. The virus that causes EEE contains RNA, or ribonucleic acid, that fits into a tiny piece of microRNA in the cells of the victim’s lymph system. This reaction suppresses the victim’s immune responses, according to researchers at the University of Pittsburgh’s Center for Vaccine Research.

Basically, the virus is sneaky and severe.

“The immune system is not warned that the virus is there,” said Ahmed. “ So the virus can build up such high levels without your body really recognizing it and spill into the brain very quickly.”

This 2013 discovery was instrumental in understanding EEE but has not been put to use to develop a vaccine yet, because the virus is just too rare, explained Ahmed.

4. Let’s talk attack rate.

Symptoms of EEE tend to show up two to 10 days after being bitten, and include fever, stiff neck, headache, and lack of energy, according to state health officials. The virus quickly leads to swelling of the brain and neurological damage.

Evidence suggests that some people who contract EEE will not experience symptoms. But Ahmed cautions against this is true of nearly every infectious disease, but the attack rate varies pathogen by pathogen and is very high for EEE.

“If you get infected, chances you will have symptoms and chances are will have very severe symptoms,” he said. “It is thought that for every case you know about of West Nile virus, there are probably 100 to 200 cases that are silent. Meanwhile, for every case of EEE, anywhere from just two to ten people don’t show symptoms.”

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To further understand attack rate, let’s talk baked goods.

Say ten hungry reporters eat a cake left in the break room. One develops food sickness and the rest just have frosting on their already rumpled clothes. The attack rate for this food sickness would be 10 percent, and more on par with EEE.

Alternatively, say 200 politicians try a pie at the Iowa State Fair. One develops food sickness and the rest just sport aviators, search for more veggie options and win stuffed animals. The attack rate for this food sickness is .5 percent, and more on par with West Nile.

5. A swamp home to the paranormal and perilous pests

The Hockomock Swamp serves a number of permissible purposes. It acts as a natural flood mechanism for southeastern Massachusetts and a water reservoir for the Town and Taunton rivers, as well as a home to sweeping wildlife and even a potpourri of paranormal tales. It also makes the region a hotbed of EEE activity since the specific mosquito that carries EEE, dubbed Culiseta melanura, primarily exists in hardwood, freshwater swamps, like Hockomock.

“For whatever evolutionary reason, the virus has coopted that species of mosquito and the virus then exists in a cycle between that mosquito and the bird population,” explained Ahmed.

Both Ahmed and Catherine Brown, the state’s epidemiologist, suggested that these birds become immune to certain strains of EEE over time, causing the decline of a cycle and the subsequent quiet years of low activity. However, the virus’ makeup adjusts slightly, pops up again and infects the birds again. And so begins the next cycle of EEE.

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This niche cycle could continue without endangering humans, but as the infected bird population balloons, promiscuous mosquito species venturing into these swamps feed on these birds and then buzz over to humans and horses for their next feeding, according to Ahmed.


Hanna can be reached at hanna.krueger@globe.com.