Dengue fever is a common tropical illness that affects millions of people yearly. Simply put, the more infections you get, the greater your chances of progression to more the serious dengue hemorrhagic fever (DHF).
Our 'What you need to know about Dengue' article generated a lot of questions in the message boards - so to further clarify the details of this devastating disease, our roving medical expert Dr. Erik McLaughlin has come back for a second round to answer your questions!
Perhaps one of the worst things to limit a traveler is heatlh. This is a conversation I have to have with patients on a regular and far too often basis. The traveler with severe lung disease that wants to trek to Everest Base Camp, a patient with seizure disorder that wants to SCUBA dive and the tropic bound patient with a history of severe dengue illness are common examples.
Dengue is the infectious agent in travelers coming home from the tropics with a fever in 2.9%-8% of the time, based on serologies (blood tests). In some case studies involving Geo-sentinel clinics, dengue is the second most comon cause of hospitalization after malaria, in travelers coming back from the tropics.
Before travel plans are cancelled, the tropics are avoided for life and mosquito-phobia sets in, let's look at Dengue and DHF from an epidemiological point of view.
What is Dengue, how many types are there and what are the symptoms?
Dengue is a flavavirus that has 4 different sero-types (dengue 1, 2, 3 and 4)
When someone gets infected with a specific sero-type of dengue they are then immune to that type for life. They can still be infected with any of the other three types. Interestingly, a person is immune to all types of dengue for the first 6-9 months after their first infection. Slowly, the immunity to the other types drops until the person is then succeptable to them as if they had no immunity at all. An individual can be infected up to four times in their lifetime.
When someone gets their initial infection with a dengue virus they often do not even notice the illness or simply attribute it to a mild "flu-like" illness. Runny nose, muscle aches, headaches, nausea and fevers are common symptoms. The characteristic dengue rash usually shows up on the 3rd day of illness. The traveler gets better and goes on with life.
If the traveler gets infected with another strain of dengue later in their life, they have an increased chance to progress to DHF. This is an illness characterized by an inability to clot blood and control vascular permeability. Bascially, the body begins to bleed uncontrollably and the veins and arteries "ooze" blood and fluid, everywhere. Untreated DHF carries up to a 50% mortality rate. If properly treated with intravenous fluids, knowledgable healthcare providers and an ICU environment, the mortality is less than 1%.
Approximately 1% of patients progress to DHF in their first infection, usually around 3-7 days after the fever starts. One study from Cuba showed 98.5% of patients with DHF had a prior dengue infection in their life. This same study also showed a DHF attack rate of 4.2% in those with a prior dengue infection who then were infected with a new serotype. Also, DHF affected white patients 5 x's more than black patients in this outbreak. This 1981 outbreak was caused by a SE Asian Dengue-2 strain.
Where is Dengue found…Exactly?
Dengue sero-types 1-4 are endemic in Africa.
Introduction and circulation of all 4 types of Dengue has been noted in the tropical and subtropical areas of the Americas since 1977.
Since the late 1990s at least two or more dengue strains have been endemic in virtually all of the Caribbean and Latin America.
Worldwide the most common sero-type is 2 followed by 3 and 4 with sero-type 1 being the most uncommon.
The Aedes mosquito is mainly associated with Dengue transmission. Aedes likes cities and urban locations much more that rural areas. Dengue is more a disease of the city that the country, as opposed to malaria.
I have never known a mosquito or a disease to respect an international boundry, line on a map or checkpoint.
I had dengue before, should I go back?
Ultimately, this is your decision.
How do you know you had dengue fever in the past? Did you get serologies and proper blood tests?
How severe was your illness, in the past?
Where are you going and what access to medical care do you have?
Are you going in the rainy season, peak mosquito time?
What are you doing there (hiking, sleeping outside, business meeting, etc?)
Do you REALLY understand insect bite precautions including DEET, permethrin and barrier devices?