Dengue Fever

Dengue fever is an illness caused by four closely related viruses (DEN-1, DEN-2, DEN-3, and DEN-4). Even though these viruses are closely related, they are recognized by the immune system as being different from each other. Thus, an infection with one virus does not provide immune protection against infections with the remaining three viral types. A person can have four bouts of dengue fever in his/her lifetime.

Dengue fever is a tropical disease. This is mainly because the virus is carried by a mosquito called Aedes aegypti. This mosquito is a normal resident of tropical climates. When the mosquito bites a human to obtain its blood meal, the virus can be transmitted to humans.

The reverse is true as well; the virus can be sucked up into a mosquito if the mosquito feeds on a dengue-infected human. The virus can subsequently be spread to another person. In this way, a large number of dengue fever cases can appear in a short time. Furthermore, if more than one of the dengue viruses is in circulation at the same time, more than one dengue fever epidemic can occur simultaneously.

Like mosquitoes, the dengue viruses have been around for centuries. The first written records of dengue fever epidemics date back to the late eighteenth century. The last major global epidemic began just after World War II. This epidemic is ongoing and has grown worse since 1990.

Dengue, also called breakbone or dandy fever (because of the severe joint and muscle pain that can result from the infection), is endemic to the tropics, meaning that the infection is always present. The dengue viruses belong to the arbovirus group. The term arbovirus is a derivative for arthropod borne, reflecting the fact that the viruses are transmitted by an insect.

The incubation period for dengue fever is usually five to eight days, but may be as few as three or as many as 15 days. Once the virus has had a sufficient incubation, the onset of the disease is sudden and dramatic. The first symptom is usually sudden chills. A headache follows and the patient feels pain with eye movement. Within hours the patient is debilitated by extreme pain in the legs and joints. Body temperature may rise to 104°F (40°C). A pale rash may appear, usually on the face, but it is transient and soon disappears.

These symptoms persist for up to 96 hours, followed by a rapid loss of fever and profuse sweating. The patient begins to feel better for about a day, and then a second bout of fever occurs. This temperature rise is rapid, but peaks at a lower level than the first episode. A rash appears on the extremities and spreads rapidly to the trunk and face. Palms of the hands and soles of the feet may turn bright red and swollen.

There is no cure for dengue. Treatment is palliative, that is, intended to ease the symptoms of the disease. Individuals usually recover completely from dengue after a convalescent period of several weeks with general weakness and lack of energy.

Recently, attenuated forms of all four dengue viruses have been developed in Thailand. These weakened viruses may be candidates for use in vaccines, even a vaccine that would simultaneously protect someone from all four versions of dengue fever. However, such a vaccine is still years from production.

No vaccine currently exists to prevent the disease. The only preventive measure that can be taken is to eradicate the aedes mosquito or to reduce exposure to them. Patients who have the disease should be kept under mosquito netting to prevent mosquito bites, which can then spread the virus.