Stay on guard for dengue fever, travellers warned
Published Monday, June 30, 2008 12:01PM EDT
TORONTO - It goes by the nickname "break bone fever.'' And after his brush with dengue, Phil Day knows why.
Day, an expatriate Canadian living in Singapore, contracted the mosquito-borne viral disease in 2007 after years of working in cities across Asia. He and his wife, Karen, were both afflicted, struggling through an illness that left them exhausted and in pain.
While they were sick, they needed to be monitored for signs they were developing the severest form of the disease, a life-threatening hemorrhagic fever. (Neither did.) That monitoring required them to go to hospital for daily blood tests. On one of those trips, Day saw a sight that embodied how he was feeling.
"We were waiting at a traffic light and this old guy, probably 90 years old or so, crossed the street with a cane. He was moving very slowly and every step looked painful,'' he recounts via e-mail.
"And I turned to my wife and said: `That's it. That's exactly how I feel.'''
Dengue is a disease of warm climes; Canada's cold winters deter the virus from setting up shop here.
But the thousands of Canadians who travel to the wide swaths of the world where the virus does spread are at some unquantifiable risk of getting infected with a virus that can trigger symptoms that range from flu-like fatigue and aching joints to a hemorrhagic fever that can kill.
A newly published study looking at trends in dengue infections in travellers notes the past 20 years have seen a marked expansion of dengue's turf, from Southeast Asia to the islands of the South Pacific, the Caribbean and the Americas. There have even been domestically acquired infections in some of the southernmost U.S. states.
Dengue has become a more common diagnosis than malaria for ill travellers returning from tropical regions except Africa, notes the study, published in the July issue of Emerging Infectious Diseases.
An analysis of cases reported to the Geosentinel Surveillance Network, an international collaboration of specialized travel and tropical medicine clinics, shows that from October 1997 through February 2006, 522 of nearly 25,000 ill travellers seen at network clinics were diagnosed with dengue or dengue hemorrhagic fever.
While that's only 2.1 per cent, it is also only a fraction of the cases that would actually have occurred during that period, says one of the study authors, Dr. Kevin Kain. Not everyone who gets sick after returning from a trip will end up at a travel clinic looking for care.
"Many people will have ... feverish illnesses that don't progress and they just stay at home,'' says Kain, director of the travel and tropical medicine clinic at Toronto's University Health Network.
"Or they present to their GP and no one ever does a confirmation test _ no one ever does serology (blood testing). So this is the tip of the iceberg, the cases we're seeing.''
Like Day, most who contract dengue get the milder illness, recover fully and hoping they'll never again do battle with the virus. That sentiment isn't simply based on the fact that the regular disease is just plain nasty.
Anyone who has had dengue fever once faces a much higher risk of developing dengue hemorrhagic fever if they contract the disease a second time. In fact, nine out of 10 dengue hemorrhagic fever cases occur in people who've previously had dengue fever, Kain says.
And since there are four strains of dengue viruses and infection with one doesn't protect against infection with one of the others, that's more than simply a theoretical risk.
"You know the story of dengue,'' Kain says.
"The first time you get it you feel like you're going to die, but you survive. But it's the subsequent infections (that are dangerous). So people want to know if they've actually had dengue, because then they're a little more apprehensive about subsequent exposures.''
Every year, an estimated 50 million to 100 million people worldwide contract dengue fever (pronounced den-gee, with the stress on the first syllable), according to the U.S. Centers for Disease Control. And several hundred thousand people come down with dengue hemorrhagic fever.
In Canada, 40 to 50 laboratory confirmed cases of dengue fever are reported every year, in travellers who have visited parts of the world where the type of mosquito that spreads the dengue virus are found.
Those mosquitoes, Aedes aegypti, like laying their eggs in the wet crooks and crannies that abound in urban settings -- discarded tires or containers and the like.
Protecting against infection poses real challenges for people travelling to the regions where the virus is found.
There's no vaccine and unlike malaria, no pills that block infection. So it comes down to DEET-based insect repellents and luck.
"It's really prevention (of mosquito bites),'' says Dr. Bonnie Henry, an infectious diseases expert with the British Columbia Centre for Disease Control, which has diagnosed two cases of dengue so far this year.
Even there, dengue offers its own challenge. "They're day biters,'' Henry says of the mosquitoes that carry the virus.
Mosquitoes that transmit malaria or West Nile virus generally bite at dusk or after the sun sets, when it may be easier to don long sleeves and long pants, or retreat to the indoors.
The disease cannot spread from person to person directly, though mosquitoes become infected by drawing blood from an infected person and then pass the virus along.
The disease typically manifests itself with a high fever, severe headache, back ache, joint pains, nausea and vomiting, eye pain and rash. Younger children generally get off with milder disease than older children and adults.
In a portion of cases, though, the hemorrhagic syndrome develops. Blood begins to pool under the skin, there can be bleeding from the nose and gums and even internal bleeding. Blood vessels become leaky, which can lead to blood loss, circulatory system failure, shock and death.
There are no antiviral drugs to combat the virus. But with good "supportive care,'' -- which largely involves replacing of lost fluids -- the vast majority of people will survive. The earlier treatment is started, however, the better.
Despite the threat it poses, dengue doesn't have the profile in Canada of a disease like malaria.
Henry says the BCCDC has been urging family doctors and infectious diseases physicians to be on the lookout for dengue and other mosquito-borne diseases in people who've recently travelled to affected parts of the world. The agency also works with travel agencies, getting them to remind clients of the risk.