Dengue is a re-emerging public health concern with two-fifths of the world population being at risk of infection. It is a mosquito-borne viral infection primarily transmitted by the bite of an infected female of the species Aedes aegypti (figure 1) and the specie_s Aedes albopictus_.
There are five serotypes of the dengue virus: DENV-1, DENV-2, DENV-3, DENV-4, and DENV-5. A person infected by one of the serotypes is immune for life against that specific strain, but is not protected against the other four serotypes.
Figure 1. Aedes aegypti is the vector that carries the virus.
Transmission of the Dengue Virus
Mosquitoes are necessary for the transmission of the virus—it cannot be spread directly from person to person. A mosquito that transmits the virus is known as a vector, or carrier, of the disease.
However, not all mosquitoes spread dengue, only those who have previously bitten an infected person (figure 2). Once a mosquito becomes infected, it remains infected and can continue to spread the virus throughout the entirety of it’s life, which is roughly 3-4 weeks.
In humans, there are two periods of interest when it comes to transmission: the incubation period, which marks the onset of symptoms; and the latency period, the period between infection and the onset of when the person can spread the disease.
The incubation period (4-10 days) provides a rough estimate of the latency period, as most individuals have been noted to become infectious within 24 hours pre or post the onset of symptoms. Once infectious, a person can transmit the infection, via the Aedes mosquitoes, for 4-5 days (with a maximum of up to 12 days).
Figure 2. Dengue transmission cycle: A healthy mosquito bites a dengue-infected human whereby the mosquito becomes infected with the virus. The dengue-infected mosquito then bites a healthy human and transmits the virus through the bite and into the blood. The cycle then starts over again.
Presentation of Dengue
After the initial incubation period, those who have become infected by the dengue virus may either be asymptomatic or go through three forms of the disease:
Dengue Fever with or without hemorrhage
Dengue Hemorrhagic Fever or Dengue Shock Syndrome
The Centers for Disease Control and Prevention (CDC) (2016), noted that up to 75 % of all DENV infections are asymptomatic, that is, they have no clinical signs or symptoms of disease.
Symptomatic dengue commonly presents as a non-specific, mild to moderate, acute, febrile illness; however, as many as 5 % of dengue infections progress to a severe, life-threatening disease—dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS).
Severe forms typically manifest after a 2-7 day febrile phase and are often preceded by warning signs.
Symptoms of Dengue
Because early clinical findings are non-specific, knowing how to recognize the warning signs of severe infection can reduce the risk of death among patients with severe dengue.
Undifferentiated fever can mimic any number of other acute illnesses with fever—it does not meet case definition criteria for dengue fever. It’s difficult to diagnose based on physical exam and routine tests alone. Unless a specfic dengue diagnostic test is performed, the diagnosis remains unknown.
Dengue Fever With or Without Hemorrhage
Dengue fever is the most common and less severe form of the virus. It begins with a sudden onset of high fever that usually lasts between 3-5 days, and is accompanied by the following symptoms:
High fever, possibly as high as 106 °F (41 °C)
Possible bleeding from the mouth and nose
Retro-orbital pain (pain behind the eyes) that is exacerbated by eye movements
Muscle and joint pain, usually in the knees and shoulders
Loss of appetite and difficulties in the sense of taste
Rash, macules, or papules on the chest and lower limbs
Nausea and vomiting
Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS)
The third clinical presentation is DHF, which may progress to DSS. Early symptoms of dengue hemorrhagic fever are similar to those of dengue fever, but 5-7 days after initial onset, the symptoms worsen and may include:
Acute epigastralgia (pain in the upper abdomen)
Bleeding of the nose, mouth or gums
Bleeding or bruising under the skin
Hematemesis (vomiting blood) and vomiting without blood
Dry skin and mucous membranes
Insomnia and restlessness
Tachycardia (high heart rate)
Tachypnea (high respiratory rate)
The most severe progression of dengue is dengue hemorrhagic shock, also known as dengue shock syndrome. It is characterized by severe low blood pressure caused by hypovolemia, or low blood volume, in relation to severe dehydration and circulatory failure.
This phase is also characterized by a significant drop in temperature, which may fool some into believing that the person is recovering, when, in fact, this is the most critical period when caregivers should be most vigilant. Without immediate and appropriate supportive care, its fatality rate is above 20 %; however, this is not the most common scenario.
The CDC illustrates the three phases of the DHF infection in figure 3, which include:
Febrile phase: high fever from viremia, virus in the blood.
Critical/plasma leak phase: sudden onset of varying degrees of plasma leak into the pleural and abdominal cavities. When plasma shifts from the circulatory system to the spaces between organs the person becomes rapidly dehydrated, resulting in hypovolemia.
Convalescence or reabsorption phase: sudden arrest of plasma leak with a naturally occuring reabsorption of plasma.
Figure 3. Phases of infection resulting in DHF (CDC, 2014).
Dengue is a disease that has spread over time. Currently, it is present in 128 countries and found in mostly tropical and subtropical areas around the world (figure 4). In the last 4-5 decades, the incidence of dengue in the world has increased significantly.
Dengue cases are underreported and many cases are misclassified.
It is estimated that 390 million dengue infections occur every year, of which 96 million have clinically manifested. Each year, about 500,000 people clinically progress to severe dengue; a large proportion of these cases are children.
About 2.5 % of all cases result in fatality.
Figure 4. Risk of dengue infection worldwide. Red indicates the highest risk of becoming infected.
Are you Planning to Travel to Central or South America? Asia? Africa?
Before traveling to areas where dengue is endemic, it is important to take certain precautions:
Research the risk of dengue in the destination you are planning to travel to on the web or in tourist offices, health agencies, etc.
Avoid mosquito-infested places within the area of your destination.
If at all possible, avoid going out during times of high mosquito activity, such as sunrise and sunset.
Wear long sleeves and pants.
Try wearing clothing that has insect shield technology built into it.
Use mosquito repellents.
Make sure doors and windows have mosquito nets and leave them closed to prevent entry of mosquitoes.
Avoid areas where there is standing water, especially during hours of high mosquito activity.
Between late 2015 and early 2016, the use of the first vaccine against dengue, Dengvaxia (CYD-TDV), or Chimerivax, was approved in several countries for people aged 9-45 years living in endemic areas. Discovery of DENV-5 and other similar strains in the future may further impede the Dengue Vaccine Initiative.
There are other live-attenuated vaccines that are currently in developmental phases and clinical trials. At present, the WHO is only recommending the dengue vaccine in areas where data signals a high burden of disease.
What Happens if I get Sick with Dengue During my Trip?
If dengue is suspected, it is very important that you visit a doctor within the region you are visiting as soon as possible.
Currently, there is no specific treatment for dengue, but early detection and medical care lowers fatality rates below 1 %.
Liquids, oral and intravenous, are supplied to prevent dehydration, and acetaminophen is used to treat high fever. It is important to avoid taking aspirin, ibuprofen, or naproxen as these can increase bleeding problems.
The condition usually lasts a week or more and is normally not deadly.
If you become sick during your trip, you should consider extending your stay until you recovered completely.
After Your Trip
If you develop dengue-related symptoms, it is important that you visit your doctor to rule out an infection by dengue. You can confuse the symptoms with an acute illness or the flu, but remember that if you are coming from an area where dengue is endemic, it is possible that these symptoms may indicate the presence of dengue. However, do not to worry, with appropriate care, rest and hydration, you can recover within a matter of a few days.
© 2007 Nature Publishing Group Adapted from Whitehead, S. S. et al. Prospects for a dengue virus vaccine. Nature Reviews Microbiology 5, 518–528 (2007). All rights reserved.