Dengue fever in travel

Dengue fever is a viral tropical disease transmitted by mosquito bites. In 2016 over 50 million new cases were reported, about ten million were hospitalized, and over ten thousand died.

Dengue is a major public health problem throughout South-East Asia and South Asia. It is also found in Queensland, Australia, the tropical South Pacific islands, Africa, tropical parts of North and South America, including the Caribbean and mainland Central America. According to the World Health Organization, dengue infections have been increasing in recent years and over half the world’s population is now at risk.

Dengue is not infectious between humans. It is transmitted to humans mainly by the Aedes aegypti mosquito, which is found in tropical regions throughout the world. The Aedes albopictus mosquito can also carry it; that one tolerates cold better and has been involved in the spread of the disease to Europe and North America. These mosquitoes carry a flavivirus which causes Dengue fever. Other flaviviruses, also insect-borne, cause Yellow fever, Zika fever, Chikungunya, the West Nile disease, and several types of encephalitis.

There are four confirmed strains of the virus and perhaps a fifth. After recovering from an infection, a patient has long-term immunity to the strain they had but only a few months reststance to other strains.

The main preventive measures are to prevent the breeding of mosquitoes and to avoid mosquito bites. No vaccine was available until recently, but in 2016 the first vaccine came on the market; see below.

Types of dengue
In most cases, dengue has a benign course. But it is important to know that there are two types of the disease:

Classical dengue: also called the common or benign type, its symptoms resemble those of the flu, causing no greater harm to health.
Hemorrhagic dengue: this, however, is very dangerous. If left untreated, it can lead to death.

Classical dengue
Classic dengue fever usually manifests as if it were a strong flu. But do not be fooled: especially if your region is showing cases of dengue, be even more aware of the following symptoms:

High fever
Generalized pain throughout the body
Severe pain behind the eyes and joints
Lack of appetite
Nausea and vomiting
Often red spots on the skin, which may resemble rubella, may be accompanied by itching

Most patients have two or three of these symptoms. High fever and aches are the most frequent. However, there is a mild form of dengue that presents without symptoms and could only be identified through laboratory tests.

Dengue hemorrhagic fever
This is the dangerous form of dengue. Therefore, I look even more open regarding the common symptoms of classical dengue fever and, if the following symptoms appear highly suggestive of hemorrhagic dengue, immediately seek medical attention:

Abdominal pain
Cough, throat inflammation, shortness of breath
Dizziness or fainting
Bleeding gums, skin (purple spots) and other body sites, as well as injection sites. In later stages, there may be vomiting and feces with blood and nasal bleeding

Signs and symptoms
About 80% of people infected with the virus have no symptoms, or only a mild fever and general malaise. Mild cases without rash may be easily misdiagnosed as flu. Dengue is also easily confused with Zika fever or Chikungunya which are caused by related viruses carried by the same genus of mosquito, are found in overlapping geographic regions, and have similar symptoms.

For the unlucky 20% or so who get full-blown dengue fever, the first symptoms are usually a sudden fever (often over 40°C, 104°F) accompanied by strong joint and muscle pains; in the 19th century it was known as breakbone fever due to these pains. This is usually soon followed by a bright red rash, most often starting on the legs but sometimes the arms and it may spread to torso and face. Splitting headaches, nausea, vomiting and abdominal pain are also common. This stage of the disease is quite unlikely to kill, but the patient may wish it would.

Symptoms usually appear 3-14 days (most commonly 4-7 days) after being bitten by an infected mosquito. The acute symptoms typically last a few days or a week, but milder flu-like symptoms often persist beyond that; many patients are miserable for weeks and for some it takes several months to fully recover. Fatality rates are around 1 in 1000, nearly all in cases that progress to dengue hemorrhagic fever.

A few cases become dengue hemorrhagic fever (DHF), in which blood vessels become more porous and start to leak fluids; fortunately this is fairly rare. The most common symptom is bleeding from the nose, mouth, and gums, but accumulation of fluids in the abdomen or lungs, bleeding in the intestinal tract, vaginal bleeding, or bleeding under the skin are also possible. There can be a fever of 42°C (107°F) or higher, which is an emergency in itself.

There are four strains of the dengue virus and DHF occurs more often in people who have recovered from an infection with one strain but then get re-infected with a different strain. The reason for this is not known for certain; one theory is that the immune system, instead of fighting the second strain, gets confused and just makes lots of antibodies against the first.

The fatality rate for DHF with proper treatment is only about 1%, but it is a life-threatening illness which usually requires hospitalization, and often some time in an intensive care ward. Treatment involves major interventions – transfusions, other intravenous fluids, sometimes oxygen to compensate for blood or lung problems, perhaps medication to reduce bleeding, and so on. The main goal is to prevent the patient from progressing to dengue shock syndrome, and this can usually be achieved.

The nastiest form of the disease is dengue shock syndrome (DSS) in which so much fluid is lost that pulse rate and blood pressure drop precipitously. This is a critical emergency; it is lethal in 90% of cases unless correctly and very promptly treated, and once the disease has progressed to this point there is risk of death even with good treatment.


There is no therapy to fight the dengue virus. The only thing to do is isolate the patient under a mosquito net in areas at risk, for a week, to moisturize regularly and eventually to administer medication analgesics and antipyretics to basic paracetamol to fight against hyperthermia and soothe the pains. The most serious cases may be heavy actions such as blood transfusions or liver dialysis. The most serious cases, fortunately rare, can be forced to rehydrate intravenously or to platelet transfusions.

There is no treatment that can attack the virus or cure the disease, only ones to alleviate symptoms such as pain, fever or nausea, or to deal with dehydration and blood loss. For mild cases, rest and fluids may be enough, but check with a doctor about other treatment.

Possible consequences
Except in the rare cases of severe dengue with haemorrhage or shock that can lead to death, the primary infection will only increase the risk of severity in case of new infection.

In areas with dengue, if you get some of the symptoms described above (especially after being bitten by a mosquito) see a doctor. The presence of dengue can be confirmed with a blood test, and much of the misery can be avoided with treatment. Not all cases need hospitalization, but most will be too ill for work or travel for anything from a few days to a few weeks.

The dengue patient should:

stay at rest
control fever and pain
in case of bleeding should be taken to the hospital.

Travel Warning:
If dengue fever is a possibility, do not self-medicate without medical advice. Some common over-the-counter medicines such as aspirin and ibuprofen, commonly sold as headache remedies, increase the risk of DHF. Any medication containing acetylsalicyclic acid or nonsteroidal anti-inflammatory agents should be avoided.

Paracetamol (acetominophen) is often used instead to manage the fever and pain.

Dengue hemorrhagic fever is a life-threatening illness; if you show any DHF symptoms, see a doctor immediately. If a local hospital has a good emergency room, go directly there.

Treating dengue hemorrhagic fever requires the resources of a modern hospital. If you are out in the boondocks and come down with dengue fever, consider evacuating immediately to somewhere with such a hospital. If your case does develop into DHF, then you will urgently need treatment but might be in no shape to travel.

If you get dengue fever during a long trip, talk to your doctor about your prognosis. The disease leaves some people debilitated (about like flu) for anything up to several months, and if you are one of the unlucky ones you may need to alter your travel plans: postpone strenuous activities and go lie on a beach or take it easy in some other way until you recover fully. Some people may even need to cut a trip short and go home to recover.

Preventive measures
Preventive measures to control and avoid dengue fever focus on avoiding mosquito bites and include:

Prevention or elimination of standing water sources, such as pools of water that collect in containers, flower pots, discarded tires or coconut shells, etc. Mosquitoes will breed in any standing water in a matter of days.
Use of permethrin-treated fabrics which kill insects that land on them.
Use of mosquito netting especially for the place you sleep in even if mosquitoes “can’t enter” the house.
Use of insect repellent (DEET or picardin are the main agents that have been shown to be most effective) as well as wearing clothing that covers exposed skin.
Houses constructed in such a way as to reduce the entry of mosquitoes. (e.g. screens on the windows a/c instead of open windows/ventilators…)
Most electronic bug zappers are not effective against mosquitoes since mosquitoes are not attracted to light. There are some models which emit carbon dioxide or octenol (found in the breath of mammals) so they do attract mosquitoes.

Protection against the vector
Avoiding dengue fever is first of all to avoid mosquito bites by taking a few precautions:

rest under a net with a mesh size of less than 1.5 mm and, if possible, impregnated with insecticide, which will protect the body parts that come into contact with the mosquito net. It is also imperative to check, every time before bedtime, if the net is in perfect condition;
use an insecticide on the inside, not forgetting the underside of the bedding and furniture;
mosquitoes being sensitive to the movement of air, the action of a fan, even if the room is equipped with an air conditioning system, will also be part of the means of protection;
coat the permethrin garments or the skin with a repellent consisting of a solution containing 30% DEET for adults or 10% of the same product for children between 2 and 12 years of age;
as much as possible, wear loose, long, light colored clothing and, if possible, refrain from consuming alcohol.
Beware that if females of anopheles, dengue propagators, are activated during the day, females of other species of mosquitoes, propagators of parasitic diseases such as malaria are active between dusk and dawn. The same precautions are therefore desirable during the night period.

The first vaccine to prevent dengue fever reached the market in 2016; it is effective against all four strains of the virus. It needs three shots six months apart, and is recommended for the age range used in testing, 9-45.

Sanofi Pasteur, the French company who developed it, are seeking approval first in countries like Mexico, Thailand, Brazil and the Philippines – places that need it and have moderately high incomes – and leaving US and European approval for later, so travellers may need to get the shot at their destination.

The vaccine was approved in Brazil, Mexico and the Philippines in December 2015 and other approvals are expected to follow. However, there are complications; the Philippine government withdrew their approval in 2017 and Sanofi no longer recommend that the vaccine be used by people who have not previously been exposed to the virus.