Dengue is a viral disease caused mainly by the infective bite of the **Aedes mosquito**, especially *Aedes aegypti* and *Aedes albopictus*. It is most common in tropical and subtropical regions worldwide, including parts of Southeast Asia, Latin America, Africa, and the Pacific Islands. Dengue infection is caused by the **dengue virus (DENV)**, with four distinct serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. Infection with one serotype confers immunity to that serotype, but not to the others.
Symptoms
Infection of Dengue ranges from mild to severe. The signs and symptoms develop 4-10 days after the infecting mosquito bite and may include high fever reaching up to 104°F or 40° C; severe headache; and pain behind the eyes.
- **Joint and muscle pain** (often referred to as "breakbone fever" since the pain can be so strong)
- **Nausea and vomiting**
- **Fatigue**
- **Skin rash** (appears within 2-5 days after the beginning of the fever)
- **Light bleeding** (such as from the nose or the gums)
In severe cases, it leads to **severe dengue**, also referred to as dengue hemorrhagic fever or dengue shock syndrome. It can consequently exhibit or lead to:
- **Severe abdominal pain**
- **Persistent vomiting**
- **Bleeding from gums or nose**
- **Blood in urine, stool, or vomit**
- **Rapid breathing**
- **Fatigue, restlessness**
- **Fluid accumulation in the lungs or abdomen**
- **Organ failure**
Severe dengue is life-threatening and requires hospitalization.
Transmission:
Dengue is spread by the bite of infected *Aedes* mosquitoes. These mosquitoes typically bite during daylight hours with peak bites occurring in the early morning and late afternoon.
Prevention:
- Mosquito control: This would involve reducing mosquito habitats, applying insect repellents, and the installment of window and door screens, among others.
- Vaccination: So far, Dengvaxia is the only licensed vaccine for dengue. It is, however, indicated only for those who have acquired a previous dengue infection due to a possible risk in those who have not.
- Personal protection: These involve the wearing of long-sleeved clothes and sleeping under mosquito nets.
Since there is no specific antiviral treatment for dengue, the basis of treatment always relies on symptomatic management, maintenance of hydration, and medical care for serious cases.
Dengue is a viral infection of the mosquito-borne variety, brought about by the **dengue virus (DENV)**, a member of the family **Flaviviridae**. There are four closely related but antigenically distinct serotypes of the virus: **DENV-1, DENV-2, DENV-3, and DENV-4**. Dengue remains one of the prime public health issues in tropical and subtropical regions and is mainly transmitted through the bite of **Aedes mosquitoes**, the most significant vector species being *Aedes aegypti* and *Aedes albopictus*.
**1. Transmission Cycle:**
Dengue virus is passed onto humans by way of the infected bite of the female *Aedes* mosquito. The mosquito becomes infected when it immediately bites a previously infected human carrying the dengue virus. Once the mosquito is infected, it can transmit the virus to other humans throughout its life. Dengue is not directly transmitted from person to person; instead, **human-to-mosquito-to-human** is how transmission occurs.
The virus can also be transmitted vertically; this occurs when the infected mosquito passes the virus onto its offspring. But this, however, is not considered to be the major route of infection in humans.
**2. Global Distribution:
Dengue infection is endemic in over 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. The WHO estimates that **half of the world's population** is at risk for dengue infection and that **100–400 million infections** occur annually.
Countries in Southeast Asia, Latin America, and Africa often report outbreaks, especially during rainy seasons when the environment is most suitable for mosquito breeding. Urban and semi-urban areas provide the most ideal conditions, especially with man-made repositories of stagnant water in which mosquitoes breed.
**3. Symptoms and Stages:**
Ideally, Dengue illness progresses through three phases:
**1. Febrile Phase (Acute Fever)**
- **Duration**: 2–7 days
- **Symptoms**: Very high fever, often as high as 104°F or 40°C; severe headache; retro-orbital pain, or pain behind the eyes; muscle and joint pains, hence the name "breakbone fever"; skin rash; nausea and vomiting; and tiredness.
- **Rash:** There may be the development of a maculopapular or petechial rash, first on the trunk, then spreading to the limbs and face.
At this stage, dehydration may occur with high fever, emesis, and poor intake of fluids.
**2. Critical Phase (Severe Symptoms)**
- **Duration**: 24–48 hours-usually 3–7 days since the beginning of fever
- **Symptoms**: In some patients, it is characterized by the sudden defervescence, but this may overlap the beginning of severe symptoms that include:
- Plasma leakage into tissues could be manifested by fluid accumulation in the lungs-pleural effusion, or in the abdomen-ascites.
- **Severe bleeding**: This may manifest as gum bleeding, nosebleeds, blood in stool or urine, or vomiting blood.
- **Shock**: Dengue shock syndrome (DSS) occurs when blood pressure drops dangerously low, leading to inadequate blood flow to vital organs.
- **Organ dysfunction**: Liver enlargement, heart failure, or neurological impairment (seizures or altered consciousness) may occur.
This phase is life-threatening and requires immediate medical attention.
**3. Recovery Phase**
- **Duration**: 48–72 hours
- **Symptoms**: During this phase, the condition of the patient stabilizes and the fluid that leaked into the tissues is reabsorbed into the bloodstream. This leads to the resolving of the symptoms of shock, which include normalization of blood pressure. However, at this stage, there is a danger of fluid overload caused by overly enthusiastic rehydration, and this needs to be watched with due caution.
**4. Complications:**
- **Severe dengue** (formerly called dengue hemorrhagic fever and dengue shock syndrome) occurs in a small but significant proportion of patients and is potentially lethal with poor management.
- **Dengue hemorrhagic fever** then represents the presence of bleeding, leakage of blood plasma, and a low count of circulating blood platelets.
- **Dengue shock syndrome** is associated with a profound fall in circulating blood volume due to severe leakage of plasma, leading to insufficient blood flow to vital organs.
**5. Diagnosis:**
Diagnosis of Dengue Fever is made by:
-Clinical manifestations: Clinically, the physician may diagnose dengue when typical symptoms are detected in the patient or upon recent travel history of the patient from/to an endemic area.
-Laboratory investigations include:
• NS1 antigen test: The presence of a dengue virus antigen can be detectable in the early phase of infection.
• PCR: The viral RNA is detectable during the acute phase of illness, mostly within the first days of illness.
- **Serological tests** [IgM and IgG]: These detect antibodies produced by the body in response to the infection, although these tests are most useful in later stages of illness.
**6. Treatment:**
There is no specific antiviral treatment for dengue. Care focuses on relieving symptoms and managing complications:
- **Fever management**: Paracetamol usually is prescribed in cases to bring down the fever and pain. Aspirin and ibuprofen are contraindicated due to their propensity towards causing hemorrhagic complications in this disease.
- **Hydration**: Oral rehydration is necessary to avoid dehydration, which may occur during the febrile phase of the disease. In severe cases, intravenous fluids may be required.
- **Hospitalization:** Severe dengue requires close monitoring for shock, bleeding, or organ failure. Blood transfusions or platelet transfusions may be necessary in serious cases.
7. Prevention:
Prevention of dengue can be done very efficiently by the avoidance of mosquito bites and control of mosquitoes. Some of the main preventive measures include:
**Remove the breeding sites**: Draining stagnating water in containers, flowerpots, tyres, etc.
Also, one will be able to protect oneself from bites through the following: Use **insect repellents** that contain DEET, picaridin, or oil of lemon eucalyptus on visible skin. Mosquito nets and screens: use bed nets and put screens onto windows and doors that allow mosquitoes into one's home. Wear **protective** clothing: a person is advised to wear long-sleeved shirts, long trousers, and socks, especially in mosquito-infested areas.
- **Community efforts**: Community-wide mosquito control programs, including fumigation, larvicide use, and public awareness campaigns, are critical in containing the spread of dengue.
**8. Vaccine:**
The first dengue vaccine, **Dengvaxia**, has been licensed for use in several countries. Its use, however, is now limited to individuals who have already been infected with dengue, due to the fact that it can result in severe illness if given to persons who never had the dengue virus. It is, generally given to individuals aged 9-45 years living in endemic areas.
**9. Dengue and Climate Change:**
More specifically, the expanding habitat of *Aedes* mosquitoes, in conjunction with global increases in temperature and altering precipitation patterns, facilitates the spread of dengue to new areas. Other factors that have contributed to this recent global explosion of dengue include urbanization, increasing population growth, and more travel.
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