The question: I’ve read news reports about an outbreak of Eastern Equine Encephalitis in the United States. It’s spread through mosquito bites and it can be deadly for people. Should I avoid travel to the U.S.?
The answer: Although the viral infection – known as “EEE” or “Triple E” – can be quite serious, the actual number of human cases is still relatively small. Public-health officials have not issued any warnings to stay clear of outbreak areas, but they urge people to take precautions to prevent mosquito bites.
Even so, this outbreak represents a worrisome development. And, in the foreseeable future, Canadians might not be able to dodge the risk of getting this infection, or other foreign mosquito-borne illnesses, by simply staying at home.
In fact, climate change and various human activities are creating ideal conditions for the establishment of invasive disease-carrying pests in Canada. Some of them are capable of transmitting EEE, Zika, dengue, chikungunya, yellow fever and West Nile viruses.
But before looking at the bigger picture, it’s worth taking a deeper dive into the EEE virus, which is found in the Eastern U.S., plus around the Great Lakes and Gulf Coast.
The virus is carried by a mosquito species called Culiseta melanura, which breeds in swampy areas and feeds primarily on birds, says Fiona Hunter, a professor of medical and veterinary entomology at Brock University in St. Catharines, Ont.
This mosquito can transmit the virus to a bird when it takes a blood meal.
To spread further, another type of mosquito usually needs to get involved – one that feeds on both birds and other creatures. So, a second mosquito species, such as Culex erraticus, can acquire the EEE virus by feeding on an infected bird, and then transmit the illness to a mammal, for example, when it dines again. Horses are especially vulnerable to the infection – hence why “equine” is in the name of the virus.
Most infected people experience only mild flu-like symptoms or feel no ill effects. However, some individuals – perhaps 2 per cent of those infected – develop encephalitis, a serious inflammation of the brain.
Of those who contract encephalitis, 30 per cent will die and survivors are often left with permanent disabilities, says Samira Mubareka, a virologist at Sunnybrook Health Sciences Centre in Toronto.
In a typical year, there are an average of seven EEE cases in the entire U.S. (One human case was reported in Canada in 2016.)
But this year, there’s been a surge in EEE activity. More than 30 cases – including 11 deaths – have been reported across seven U.S. states.
Experts are at a loss to explain why 2019 could end up being one of the worst years on record for EEE.
Many of them are concerned that this may be a harbinger of things to come for a wide range of mosquito-borne infections.
Hunter and her research colleagues have been monitoring the encroachment of new mosquito species into Canada. Over the past two decades, at least a half-dozen foreign mosquito species – capable of spreading sicknesses – have been found at sites in Southern Ontario.
“With climate change, our habitat is becoming more conducive to southern mosquitoes moving in and flourishing here,” Hunter says.
Global trade is another source of invasive pests, which can hitch a ride in goods destined for North America.
“Aedes albopictus, or the Asian Tiger Mosquito, is breeding quite happily near Windsor, Ont.,” Hunter says. “We first picked it up in 2016 and the population has expanded further afield each year.”
It’s not only a potential West Nile virus transmitter, but Aedes albopictus can also spread Zika, dengue and chikungunya – illnesses once considered to pose little or no peril to Canada.
“At this point, there is no need to alarm people,” she says, adding that the current risk is small. “But 20 years from now, it could be a different story.”
Hunter points out that it’s costly and challenging to develop vaccines. Furthermore, government insect control programs aren’t very effective.
That means the onus will likely fall on people to adopt their own defensive measures against mosquito-borne diseases, such as covering up with appropriate clothing and using insect repellent.
“It’s just good to protect yourself from mosquito bites because we never know what threat might be around the corner,” Hunter says.
Paul Taylor is a patient navigation adviser at Sunnybrook Health Sciences Centre. He is a former health editor of The Globe and Mail. Find him on Twitter @epaultaylor and online at Sunnybrook’s Your Health Matters.
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