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Dengue Fever

Dengue Fever Biology

The dengue virus is spread through a human-to-mosquito-to-human cycle of transmission, with the mosquito Aedes aegypti. How do dengue viruses infect human cells and replicate themselves? How does the body respond when it is infected with dengue? What factors put some people at a greater risk of severe dengue illnesses than other people?

1.1

What Is Dengue Fever?

Approximately 2.5 billion to 3 billion people around the world are currently at risk of dengue infections. The symptoms of dengue can vary widely, although some patients show no symptoms at all. The classic symptoms of dengue include a high fever, severe pain in the muscles, bones, and joints, pain behind the eyes, severe headaches, nausea and vomiting, and a rash. Most patients recover from dengue infections with rest and fluids. Some patients develop severe dengue, a more serious condition that occurs when blood plasma leaks through the capillaries. Severe dengue can lead to internal bleeding, shock, and organ failure. When treated quickly with intravenous fluid replacement, most patients recover from severe dengue. There is currently no cure for dengue and no vaccine to prevent dengue infections.

1.2

Dengue Transmission

The dengue virus is spread through a human-to-mosquito-to-human cycle of transmission, with the mosquito Aedes aegypti as the primary vector. These mosquitoes live near humans in tropical and subtropical regions of the world. Female Aedes aegypti become dengue vectors after feeding on the blood of a person infected with the dengue virus. Infected mosquitoes continue to transmit dengue with each blood meal for the rest of their lives. Aedes aegypti have a complex life cycle that includes aquatic and terrestrial stages. These mosquitoes lay their eggs inside containers, and new Aedes aegypti hatch when the containers are filled with water. Dengue poses the greatest risk in highly populated regions with rainy seasons where there are large populations of Aedes aegypti with a high degree of contact between the mosquitoes and humans.

1.3

Dengue Viruses

Like other viruses, the dengue virus is a microscopic structure that can only replicate inside a host organism. The four closely related dengue viruses — DEN-1, DEN-2, DEN-3, and DEN-4 — are found in the same regions of the world. The dengue virus has a roughly spherical structure. It is composed of the viral genome and capsid proteins surrounded by an envelope and a shell of proteins. After infecting a host cell, the dengue virus hijacks the host cell's machinery to replicate the viral RNA genome and viral proteins. Newly synthesized dengue viruses can go on to infect other host cells.

1.4

Host Response to the Dengue Virus

Dengue viral infections can result in a range of symptoms. Some people show no symptoms or only have mild signs of the disease. Other people develop severe complications. How does the body respond to a dengue infection? What factors put some people at a greater risk of severe dengue illnesses than other people? The human body's immune system is the primary defense against the dengue virus. When someone is infected with dengue, the body's innate and adaptive immune responses work together to fight the virus. B cells from the immune system produce antibodies that recognize and neutralize dengue viral particles, and cytotoxic T cells recognize and kill cells that are infected with the virus. People who are infected a subsequent time with a different type of the dengue virus may experience something called "antibody-dependent enhancement" in which the body's immune response actually makes the clinical symptoms of dengue worse and increases a person's risk of developing severe dengue.

Unit 2

Controlling Dengue Fever Outbreaks and Developing Future Treatments

Controlling and preventing dengue fever outbreaks are essential steps to managing the disease. What methods are being used and developed to control dengue in regions where its threat is high? How can scientists better diagnose and treat dengue patients and limit the effect of epidemics? What types of vaccines and antiviral drugs could be used to treat and protect people from dengue infections?

2.1

Controlling Dengue Outbreaks

In the absence of an effective vaccine that protects humans from dengue, limiting contact between people and vectors is the most effective way to prevent dengue infections. Environmental management approaches involve eliminating the container habitats in which Aedes aegypti lay their eggs. Chemical control involves the use of insecticides to kill immature or adult mosquitoes. New chemical, biological, and genetic approaches are being developed and may provide promising alternatives to control mosquito populations and prevent dengue infections.

2.2

Current Dengue Fever Research

Dengue has become a serious health problem worldwide, and scientists are focusing their attention on understanding how the dengue virus causes disease. As they learn more about how dengue affects the body, researchers hope to diagnose and treat dengue better. Current dengue research also aims to provide better surveillance to limit the effect of dengue epidemics. What approaches are scientists using to improve the diagnosis and treatment of dengue patients, and how can researchers reduce the threat of dengue epidemics?

2.3

Future Dengue Fever Treatments

Researchers are making substantial progress in developing safe and effective vaccines against the dengue virus. Currently, a large number of dengue vaccine candidates are being tested in preclinical and clinical trials for safety and effectiveness, and within the next several years, a safe, economical vaccine for dengue may be commercially available. Scientists are also developing antiviral drugs that they could distribute to people during dengue epidemics to decrease the risk of dengue.

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