Dengue fever
Overview
Dengue fever is a mosquito-borne tropical disease caused by the dengue virus. It is transmitted by several species of mosquito within the genus Aedes, principally Aedes aegypti. Symptoms typically begin three to fourteen days after infection and may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic skin rash. Recovery generally takes two to seven days. In a small proportion of cases, the disease develops into the life-threatening dengue hemorrhagic fever, resulting in bleeding, low levels of blood platelets, and blood plasma leakage, or into dengue shock syndrome, where dangerously low blood pressure occurs.
Epidemiology
Dengue fever is endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia, and the Western Pacific. The World Health Organization (WHO) estimates that there are about 50–100 million dengue infections worldwide every year. The incidence of dengue has increased 30-fold over the last 50 years, with the disease now being endemic in many countries. The spread of dengue is attributed to urbanization, increased human travel, and climate change.
Virology
Dengue virus (DENV) is a single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus. There are four distinct serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) of the virus that cause dengue. Infection with one serotype usually provides lifelong immunity to that serotype but only short-term immunity to the others. Subsequent infection with a different serotype increases the risk of severe complications.
Transmission
The primary vector of dengue is the Aedes aegypti mosquito, which thrives in urban environments and breeds in standing water. The virus is transmitted to humans through the bites of infected female mosquitoes. The mosquitoes become infected when they bite a person already infected with the virus. Once infected, a mosquito can transmit the virus for the rest of its life.
Pathophysiology
After entering the human body, the dengue virus infects and replicates in white blood cells. The infected cells move throughout the body, releasing the virus into the bloodstream. The immune system responds by producing a range of signaling proteins, such as cytokines and interferons, which are responsible for many of the symptoms of dengue fever. Severe disease is thought to occur when a person who has previously been infected with one serotype is infected later with a different serotype. This phenomenon is known as antibody-dependent enhancement (ADE).
Clinical Manifestations
Dengue fever presents with a sudden onset of fever, severe headache, pain behind the eyes, severe muscle and joint pains, nausea, vomiting, swollen glands, and rash. The rash may appear two to five days after the fever starts. In some cases, the disease progresses to severe dengue, characterized by plasma leakage, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. Severe dengue can be fatal if not managed properly.
Diagnosis
Dengue fever is diagnosed by clinical presentation and confirmed by laboratory tests. The most common diagnostic methods include:
- **Serological tests**: Detect antibodies produced in response to the dengue virus.
- **Molecular tests**: Detect viral RNA in the blood using techniques such as reverse transcription-polymerase chain reaction (RT-PCR).
- **Antigen detection tests**: Identify dengue virus antigens in the blood.
Treatment
There is no specific antiviral treatment for dengue fever. Management of the disease focuses on supportive care to alleviate symptoms. This includes maintaining proper fluid balance, pain relief with acetaminophen (avoiding nonsteroidal anti-inflammatory drugs like aspirin and ibuprofen due to the risk of bleeding), and close monitoring for signs of severe disease. Hospitalization may be required for severe cases to provide intravenous fluids and blood transfusions if necessary.
Prevention
Preventing dengue fever involves controlling mosquito populations and minimizing exposure to mosquito bites. Key strategies include:
- **Eliminating mosquito breeding sites**: Removing standing water where mosquitoes lay eggs.
- **Using mosquito repellents and insecticides**: Applying repellents on skin and clothing, and using insecticide-treated bed nets.
- **Wearing protective clothing**: Long-sleeved shirts and long pants.
- **Vaccination**: The Dengvaxia vaccine has been approved in some countries for individuals aged 9–45 years who have had at least one previous dengue infection.
Public Health and Control Measures
Public health measures to control dengue fever include community education, vector control programs, and surveillance. Governments and health organizations work together to implement integrated vector management (IVM) strategies, which combine biological, physical, and chemical methods to reduce mosquito populations. Public awareness campaigns educate communities about the importance of eliminating mosquito breeding sites and protecting themselves from mosquito bites.
Research and Future Directions
Research on dengue fever is ongoing, with efforts focused on developing more effective vaccines, antiviral treatments, and vector control methods. Advances in genetic engineering and biotechnology hold promise for innovative approaches to combat the disease. For example, the release of genetically modified mosquitoes that are resistant to dengue virus or that produce sterile offspring is being explored as a potential strategy to reduce mosquito populations and interrupt transmission.