Dengue fever is a painful severe mosquito-borne disease caused by any one of four closely related dengue viruses. This disease is most prevalent in tropical areas of the world. However, it is not contagious. It is caused and spreads mainly through infected mosquito bites

Out of the 400 million dengue infections that occur worldwide every year, about 96 million fall sick and develop symptoms – that is about one in four people infected with the virus will get sick. The symptoms can be mild or severe. If the symptoms are severe, hospitalization is often required.

The dengue disease can develop into a more severe form. This is called severe dengue, dengue hemorrhagic fever (DHF), or dengue shock syndrome.

DHF mainly affects children who are below 10 years of age. It can also develop if you have developed dengue fever a second before fully recovering from your first infection.

The dengue mosquito

Dengue is a viral infection transmitted to humans through the bite of an infected female mosquito mainly of the Aedes species. The other vector that transmits the disease to a lesser extent is the Ae. albopictus.

Aedes aegypti is a mosquito that can spread dengue fever, chikungunya, and yellow fever. It is characterized by black and white markings on its legs and a marking in the form of a lyre (a U-shaped stringed instrument of the harp class) on the upper surface of its chest.

This mosquito first originated in Africa but is now found in tropical, subtropical, and temperate countries throughout the world.

In spite of the fact that Aedes aegypti mosquitoes usually feed at sundown and morning, indoors, in sheltered areas, or in cloudy weather, they can bite and spread infection all year long and at any time of day

Dengue virus

The virus that is responsible for causing this disease is called dengue virus (DENV). There are four related DENV viruses: DENV-1, DENV-2, DENV-3, and DENV-4. A person can, therefore, be infected with this virus as many as four times in his or her lifetime.

Once you have recovered from dengue infection, it provides you lifelong immunity against that particular virus serotype that had infected you.

However, after recovery, immunity developed to the other serotypes is only partial and temporary. Subsequent infections caused by other serotypes increase the risk of developing dengue hemorrhagic fever.

Transmission – How dengue spreads

Transmission of the dengue virus can occur in the following ways

1. Through Mosquito Bites

Dengue viruses enter the body through the bites of the infected Aedes species mosquitoes.

These mosquitoes lay eggs in standing water that may be present in various ways such as in containers, vases, long-standing puddles, etc

These mosquitoes bite people and can do so indoors and outdoors, during the day and night. Mosquitoes become infected when they bite an infected person harboring the virus. Infected mosquitoes can then spread the virus to other people through bites.

2. From mother to child

A pregnant woman already infected with dengue can pass the virus to her fetus during pregnancy or during delivery.

3. Through infected blood, laboratory, or clinical apparatus

Rarely, dengue can spread through blood transfusion, organ transplant, or a needle stick injury.

Symptoms and signs

Most people do not develop any symptoms of dengue fever.  Approximately, 50% of infected individuals will remain entirely asymptomatic.

In the other symptomatic patients, symptoms set in 4 to 10 days after the mosquito bite. This is called the incubation period. Dengue symptoms can mimic symptoms of other illnesses such as flu. Fever and muscle and joint pains are the first symptoms to appear.

Typical symptoms include:

  • High fever that can go as high as 104 degrees °F
  • Severe headache
  • Muscle or joint pain
  • Nausea
  • Vomiting
  • Retro-orbital pain
  • Swollen glands
  • The skin rash typically appears over the face, thorax, and flexor surfaces.

Symptoms tend to last for a week and most people recover after that.

In some cases, the dengue infection can become severe and be life-threatening. In severe dengue, your blood vessels suffer damage and as a result, they leak and cause bleeding. The platelet levels in the blood fall. This can lead to shock, internal bleeding, very low blood pressure, organ failure, and even death.

The symptoms and warning signs of severe dengue cases tend to develop quickly.

They include:

  • Severe abdominal pain
  • Vomiting
  • Bleeding may occur from your gums or nose
  • Blood in your urine, stools or vomit
  • Bleeding beneath the skin, which looks like bruising
  • Difficulty in breathing
  • Fatigue
  • Irritability or restlessness

Diagnosis

Early and accurate diagnosis is of crucial importance for clinical care. This can be done from a serum specimen obtained within 7 days after fever onset.

There are two main types of blood tests to diagnose dengue infection. One looks for the virus itself; the other checks for antibodies that may have developed because of the virus.

Your doctor may order these tests if you are down with fever, muscle pain, weakness, or any other dengue symptoms because a lab test is the only way to confirm this infection.

1. Dengue NS1 Antigen test

The NSI antigen test is advised within the first 5 days of the onset of symptoms because NS 1 antigen starts to appear in the blood from the first day of infection and may stay present for up to 5-7 days. Thereafter, it starts disappearing from the blood and the test may give a false-negative result.

2. Dengue RT-PCR test – NAAT

A NAAT Nucleic Acid Amplification Test is a generic term referring to molecular tests used to detect viral genomic material.

The RT-PCR test is the most sensitive and specific test used to detect dengue virus during the first 5 to 7 days after the onset of fever. It detects the genetic material of the virus in the blood.

A positive result of this test not only confirms the infection but also helps to identify the serotype of the virus. This test is about 90% sensitive and 95% specific against the infection.

3. Immunoglobulin M (IgM) test for Dengue

This test detects IgM antibodies in the blood. These antibodies appear in the early stages of the disease and indicate an ongoing acute infection or a recent infection.

These antibodies start developing 4 to 5 days after the infection has set in. Therefore, this test is advised after 4 to 5 days of the occurrence of the symptoms.

4. Immunoglobulin G (IgG) test for Dengue

IgG test for dengue is advised after 14-21 days of infection or even later because the IgG antibodies stay in the blood several months after the infection has subsided. However, at this time, these antibodies are detectable in low counts. But, later they slowly increase.

They can remain in the blood for about 90 days and in some cases, they may be detected in blood for the entire lifespan.

The presence of IgG antibodies signifies recovery from past infection or after vaccination against dengue.

3. Complete blood count

Dengue is very often associated with decreased platelet count and low WBC count (thrombocytopenia and leucopenia). The primary function of the platelets is to stop bleeding by clotting. Thus, if the platelet count drops too low, it can cause bleeding that will be difficult to stop.

Therefore, the platelet count should be monitored carefully and regularly in such patients, especially after the fever comes down.

Summary:

·         While Dengue RT-PCR remains the most sensitive and specific test for dengue, NS1 antigen & IgM tests done together are also useful in detecting early infection.

  • In the 1st week of the onset of symptoms, a dengue PCR test and NS1 antigen are recommended.
  • Between the 3rd to 9th days, a combination of NS1 antigen/ PCR and IgM antibodies is recommended.

Treatment

There is no specific treatment available to completely eliminate dengue infection from the body.

The focus of treatment is to manage and improve the symptoms and ask the patient to take sufficient rest.

Fever and body aches can be treated with antipyretic drugs like paracetamol.

Avoid aspirin and NSAIDs such as ibuprofen, because they increase the risk of G.I. hemorrhage.

Antibiotics or Antivirals have no role to play as these generally do not help in managing dengue fever.

The mainstay of dengue management is to stay well hydrated by drinking plenty of fluids and eating a well-nourishing diet.

Stay in touch with your doctor who will monitor your condition and platelet count. This is to know immediately if you are showing any warning signs of hemorrhagic dengue fever such as uncontrolled fever, loose motions, cold clammy skin, low blood pressure, decreased appetite, weak pulse, pain in the abdomen, or dark stools. The onset of these symptoms may require hospitalization.

Hospitalization will provide for proper fluid balance, which is critical for patients with dengue hemorrhagic fever and can decrease the mortality rate by 50 to 100-fold.

How you can prevent getting dengue?

Dengue is caused by a mosquito bite. Therefore, the best way to prevent dengue is to stay protected against mosquitoes. Here are some effective ways to prevent mosquito bites and dengue.

  • Use mosquito repellents
  • Use a mosquito net while sleeping
  • Protect windows with nets
  • Stay fully covered with full sleeve shirts and full length trousers
  • Avoid water stagnation in and near your house.
  • Spray insecticides in your house and around

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