Kaylee Hardenbrook is one of the lucky ones. Five years ago, a 31-year-old mother of two went to the emergency room with flu-like symptoms. Doctors sent her home and her symptoms worsened. After a few days, Hardenbrook had a seizure and became comatose.
When she woke up, the doctors told her to arrange to say goodbye to her children. "They said my brain was a mess," Hardenbrook said.
The culprit, it turns out, is a rare mosquito-borne virus called Eastern Equine Encephalitis (EEE), which is cultivated every year in groups along the East Coast, the Great Lakes and the Gulf Coast.
Hardenbrook, who is from Paw Paw, Michigan, who rests in one of the many lakes in the state, had never heard of EEE before being diagnosed.
"There was no talk in my area," she said.
This is beginning to change. Although the EEE virus usually infects about seven people a year, 28 cases have been reported so far, including 10 in Massachusetts and eight in Michigan, according to the Centers for Disease Control and Prevention. Nine people were killed.
These numbers make 2019 the worst year for EEE in decades – the CDC began tracking the disease by the early 1960s – with a previous peak of 21 cases in 2005.
Mark Fischer, an epidemiologist in the CDC arbovirus disease industry, stressed that it was premature to claim that the threat of EEE in the US was increasing.
EEE appears cyclically in affected areas, with two to three years of intense activity, followed by a prolonged period of attenuating infections.
"This is typical," he said of the fluctuations year by year. "This is just one senior year. There is no evidence that we have a long-term trend."
Compared to other mosquito-borne diseases, such as West Nile disease, EEE is incredibly rare. By the end of September, there were reports of CDCs in 2019 with 543 cases of West Nile disease.
This does not mean that EEE does not apply. Although unusual, it is among the most fatal mosquito-borne infections in the United States. "It's a serious disease," Fisher said.
The virus infects many people, but according to the CDC, only 5% of mosquito bites develop any symptoms that may include flu-like indicators (fever, chills, body aches), even to severe neurological conditions from brain edema. (encephalitis). Of the small subset of people who develop brain edema, there is a 30% risk of death. Among those who survive, many will continue to experience neurological problems such as seizures, intellectual disabilities and personality disorders.
Hardenbrook was among those miserable 5%. She told ABC News that she had developed meningitis and was temporarily paralyzed. She had to learn to walk and use the bathroom. But today, apart from minimal memory loss, it feels much better.
"I want to inform people that there is still hope," she said of her return from EEE against the odds. "I'm very lucky."
Part of the passion for EEE could be the combination of high mortality and severe and lasting health problems that many survivors experience. By comparison, West Nile mostly affects people who are older than 60, explained Scott Weaver, a virologist at the University of Texas Medical Branch.
"I think these factors have an emotional impact and cause more fear," Weaver said.
There is no preventive human vaccine against infection with the EEE virus and no antiviral treatment once acquired. Medical teams can only offer supportive care to help minimize symptoms.
What is the cause of this year's record-breaking EEE cases
The causes of this year's developments are complex and still unknown.
EEE occurs naturally in birds living in freshwater marshes that maintain large mosquito populations. Insects feed on these animals, become infected and subsequently transmit the virus to susceptible human hosts during subsequent blood meals.
Changes in bird and mosquito populations, meteorological factors such as warmer, wetter conditions and human behavior, such as spending time outdoors without mosquito protection, all play a role in infection rates. Enhanced surveillance and diagnosis can also contribute to the jealousy of confirmed EEE cases. If more people are aware of a disease threat in a given year, they are more likely to be tested and diagnosed, Fisher explained.
This year, the jump in infections also prompted researchers to wonder if the virus was developing and becoming more dangerous,
Catherine Brown and her team at the Massachusetts Office of Infectious Diseases and Laboratory Genetics have analyzed two decades of EEE virus data. The researchers found that the virus had developed in Florida, which could lead to new and potentially more severe northeast strains.
Edward Walker, a professor at Michigan State University in the Department of Entomology, attributed increased EEE cases to older mosquitoes. As mosquitoes progress, the likelihood of contracting a diseased animal and transmitting this infection to humans increases because these mosquitoes have taken more blood meals throughout their lives.
The wait for the first big frosts
The good news for countries like Michigan and Massachusetts that have taken the brunt of this year's EEE cases is that the seasonal window for the transmission of the virus is approaching.
"As the autumn progresses and temperatures cool, we expect the number of human cases to decline," Fisher said.
Weaver noted that the first solid frost, usually around mid-October to the northeast, tends to kill much of the adult mosquito population.
Until then, health officials have recommended removing any standing water around the home, wearing long sleeves, using EPA-registered mosquito repellent (such as Deet Picaridin and lemon eucalyptus oil) and limiting the time spent open after dusk.
Because EEE tends to affect specific areas, it is more important for people in these states and regions to comply with the recommendations than for those outside the traditional disease area. In Michigan and Connecticut, where two EEE people died this year, schools are adjusting outdoor sports schedules to avoid mosquitoes in the evening.
Hardenbrook's husband, who is an avid hunter, always takes mosquito protection when in the woods these days. But in the last few years, it has not even come out on opening day.
"It was so warm," Hardenbrook explained.
In addition to preventing mosquito bites, Walker supports mosquito control efforts, including aerial spraying in areas where positive EEE mosquitoes have been found. Several affected areas in the Northeast have now increased the practice of spraying.
Experts are divided on whether climate change is making things worse
While the virus is difficult to study because of its sporadic nature, Theodore Andreadis, director of the Connecticut Agricultural Experiment Station and head of the Center for Vector Biology and Zoonotic that climate change may be linked to an increase in the emergence of EEE.
He notes that climate ecological models predict longer summers and milder winters, which can lead to overwintering, which is when a mosquito survives in the winter, which allows the virus to survive, too.
"By 2003, cases in the Northeast were very sporadic," Andreadis said. "We are now seeing more outbreaks in regions where EEE has not been detected so far. We know that the virus persists for several years and the strain is fading."
Extreme weather, such as heavy rainfall and wet conditions, can create ideal breeding habitats to support larger mosquito populations. More mosquitoes mean additional chances for insects to acquire EEE and to transmit the disease more quickly.
Fisher, a CDC epidemiologist, said there was no way to link climate change to this year's disease spike.
"I would associate it more with meteorological models," he said, noting that the weather could change with time. Fischer said long-term changes to these models could be a problem.