What is Eastern Equine Encephalitis (EEE)?
It is a viral disease that can be transmitted to humans through the bite of an infected mosquito.
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The EEE virus is mainly found in one particular species of mosquito, but all mosquitoes can carry the virus.
“There is no antiviral treatment for this disease and no vaccine for humans,” emphasizes Miarisoa Rindra Rakotoarinia, scientific advisor to the National Institute of Public Health of Quebec.
The incubation period is 4 to 10 days. Most infected people do not have any symptoms. Sometimes, you may have flu-like symptoms (fever, muscle aches).
However, in 5% of cases, the virus can infect the brain. A severe form of the disease then appears, which can develop into meningitis or encephalitis, with more alarming symptoms: vomiting, convulsions or even coma.
When the brain is affected, the mortality rate is 25 to 75%. Death can occur 3 to 5 days after the onset of symptoms. Of those who survive these severe forms of the disease, about half are left with permanent neurological damage.
Why are we talking about this now?
“This disease has been known for a very long time: the first cases were detected in horses two centuries ago in the United States,” explains the infectiologist. Donald Vinh, a physician at the McGill University Health Centre. “And it was first identified in humans in 1938.”
The disease is mainly present in a particular species of mosquito, which prefers to bite birds. But other mosquitoes, less fussy about their prey, can also become infected by biting a bird carrying the virus, before infecting another host. This could be a horse, for example, or a human.
About ten cases are reported in humans each year in the United States. Several have recently been reported in New England, and a 41-year-old man from New Hampshire died of the disease on August 19.
What is the situation with us?
In Quebec and Ontario, it is not uncommon for cases to be reported in horses. Several were reported in August this year, according to the Canadian Animal Health Surveillance System database.
Only four cases have been detected in humans in Ontario since 2016, the most recent in 2022. But “all have survived,” assures Mme Rakotoarinia.
In Quebec, no human cases have been reported so far. But since horses have been infected, “it’s pretty certain that the virus is circulating here too [chez l’humain]but that it went under the radar,” emphasizes the veterinarian. Antoinette Ludwig, epidemiologist at the Public Health Agency of Canada.
Who is at risk?
Children and the elderly are most at risk of developing severe disease if they become infected. “Cases always occur on the outskirts of marshy areas,” notes Dr.D Ludwig, because that’s where the species of mosquito that infects birds lives.
She recommends taking special care when traveling in forests or near marshes. People working in agricultural areas or with horses are also more likely to be bitten by an infected mosquito.
How does this virus compare to others?
EEE virus is not the only one transmitted by mosquitoes; in Canada, health authorities also monitor West Nile virus, as well as those of the California serogroup.
In rare cases, these viruses can also cause serious neurological infections.
In particular, the species of mosquito involved in transmitting West Nile virus prefers urban environments. That’s why experts recommend taking precautions to avoid being bitten at all times, including in the city.
What can we do to protect ourselves?
“You shouldn’t panic as soon as you get bitten,” emphasizes Dr.r Donald Vinh: “But you have to be careful when there is an overabundance of mosquitoes.”
To avoid being bitten, experts recommend wearing loose, covering clothing, avoiding going out at night – when mosquitoes are particularly active – or using repellent.
Read “Help, Mosquitoes Love Me!”
And in the future?
For the DD Ludwig, if we see cases of EEE in horses more regularly than before, and now in humans, it is not by chance. “There is a link with climate change,” she assures.
In the coming years, as temperatures rise, mosquitoes are likely to become more active and will be able to reproduce more easily. “The virus will also be able to multiply faster, which will accelerate its transmission,” she explains.
Likewise, experts expect more rainfall, which could benefit mosquitoes, since they thrive in stagnant water.
Disease-carrying populations could thus increase and move. The researcher therefore expects to see cases of EEE multiply in the future in Quebec.