What is Dengue fever? viral fever, travelers disease, travelers fever, mosquito spreading disease

Dengue is a viral disease, commonly transmitted by a mosquito called Aedes mosquito. It is a common disease in some parts of the world- parts of Asia and America where the disease is endemic.  In the rest of the world the disease most often is brought in by travellers (70 to 80%) who visit these endemic areas. About 100 million people get infected by dengue virus every year, so it is important that we know more about dengue and develop methods to prevent it. There is no vaccine or prophylactic drug or medicine available to prevent it.

The Aedes mosquito is a funny guy: he prefers to bite and drink human blood during the day time and hide and rest in dark areas. The female mosquito whose average life span is 8 to 14 days lays eggs in damp places that can remain viable for months.

What causes dengue?

Dengue is caused by the dengue virus which is a RNA virus belonging to the flavivirus genus. A person gets the virus when he is bitten by the dengue virus carrying mosquito. Once the virus enters the body the person may manifest with signs and symptoms of the disease which the WHO classifies as dengue fever and severe dengue fever.

 How does the World Health Organization classify dengue?

The WHO classifies Dengue as dengue fever and severe dengue fever.

Dengue fever

Acute febrile illness, live in or travel to endemic region, with two or more of the following:

Nausea and/or vomiting

Headache and/or retro-orbital pain and back pain

Aches and pains

Rash

Tourniquet test positive

Leukopenia

Any warning signs (abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy, liver enlargement, increase in hematocrit, falling platelet count with laboratory confirmation)

Severe Dengue Including Dengue Shock Syndrome

Severe capillary permeability and plasma leakage leading to dengue shock syndrome

Fluid accumulation and respiratory distress

Severe bleeding

Severe organ involvement (liver, CNS, heart, kidneys, and others) 

What are the signs and symptoms of a patient suffering from dengue?

In its uncomplicated course dengue fever manifest with fever that may have associated with rashes, aches and pains. Sore throat, coryza, cough, anorexia, nausea, vomiting, diarrhoea, headache, back pain, myalgia, arthralgia, and conjunctivitis also may occur.  It usually subsides over period of time with supportive treatment. However in contrast, in severe dengue fever the walls of our blood vessels become damaged and unable to properly function. As a result our plasma leaks out and the blood pressure may rapidly come down- ending in shock stage called Dengue shock syndrome. Platelet cells that are needed for normal blood clotting mechanism also can be abnormal or decrease to dangerous levels so that bleed can easily occur in these patients. The capillary leakage can end up in lung edema- pulmonary edema, pleural effusion and fluid in our peritoneal cavity- ascites. Bleeding tendencies can result in skin bleeding- petechiae, mucosal bleeding, peptic ulcer bleeds, menorrhagia and others. In severe cases intracerebral (brain) and pulmonary (lung) bleeding can also occur. FDP or Fibrin degradation products have not been found to be elevated to a degree consistent with classic disseminated intravascular coagulation (DIC). Some patients may also develop encephalopathy, pneumonia, and liver dysfunction.

In mild grade of dengue the virus or viral load can be tackled by our immune system. However in the severe grades of dengue the increasing virus numbers outdo our immune system (by  enhanced infection of monocytes in the presence of pre-existing anti dengue antibodies at sub neutralizing levels thereby leading to antibody-dependent immune enhancement) and therefore presents with severe problems affecting all the body systems slowly.

What are the diseases that may be confused with dengue fever? (Differential diagnosis)

A number of diseases can be confused with dengue and this will depend on the region where the patient resides, at what stage the patient presents to the doctor and also the season it occurs:   measles, rubella, enterovirus, influenza, scrub and murine typhus, septicemia, other viral hemorrhagic fevers (e.g., Ebola, Lassa fever), chikungunya, West Nile fever, o’nyong-nyong fever, malaria, typhoid, leptospirosis, hepatitis A, rickettsiosis, Hanta virus infection, and Rift Valley fever.

How do we confirm that the patient has dengue infection?

Once the diagnosis of dengue- like disease is thought of after a through history taking and clinical examination, one must confirm the diagnosis.  Laboratory confirmation is by the following means:

 1) Serologic confirmation in acute dengue infection -demonstration of specific immunoglobulin IgM and IgG antibodies against dengue in the serum of patients

2) RT-PCR - Dengue virus RNA also can be amplified by reverse transcriptase nested polymerase chain reaction (RT-PCR) from serum

3) Viral isolation-culturing the patient's serum with Aedes albopictus C6/36 cell monolayers and confirming the virus infection of these cells by immunofluorescent assay using a flavivirus-specific monoclonal antibody.

How is dengue infection treated?

Patients may present with dengue fever or severe dengue complicated by shock. Careful clinical assessment with added laboratory investigations will show grade of dengue infection.  There are no specific drugs for dengue so uncomplicated dengue fever will need good supportive care.

In severe dengue the plasma leak and the clotting abnormalities are the main problems that need to be tackled. Hypotension and shock must be treated by judicious fluid resuscitation. The blood volume must be brought back to normal otherwise the shock will progress to organ failure and death. The patient's mental status, pulse, temperature, respiratory rate, blood pressure, central venous pressure, oxygen saturation and urine output must be measured frequently and checked. Regular hematocrit evaluation will show if any hemoconcentration is present. The blood volume restoration may need isotonic crystalloid solutions, plasma or colloid solutions like starch, dextran and others as deemed by the physician.

(For professionals treating dengue- In patients with dengue shock, studies have suggested that ringer lactate solution should be started at a rate of 15 to 20 mL/kg over 1 hour. The patient should be monitored (by various parameters mentioned before) as then the rate can be reduced to 10 mL/kg/h for 2 hours. As his condition improves it may be reduced to 7.5 ml/kg/ hr. for 2 hrs. then 5 mL/kg/h for 4 hours, then 2 to 3 mL/kg/h for 24 to 36 hours. If the clinical condition stabilizes then the fluids can be stopped after this period. After the first hour of resuscitation colloid solutions or plasma expanders (6% dextran 70 or 6% starch solution) should be added as needed by the physician if ringer's by itself is unable to tackle the circulatory collapse. The plasma leak takes time to settle down and that usually happens by the 7th day. Children and those below one year as well as those with cardiac or renal diseases will  need special care since they are unable to withstand fluid disturbance or blood volume changes as adults.)

The presence of co morbid conditions like cardiac diseases and lung diseases will play a great role in the recovery of the patient. Each body system like the lung and the heart will have to be observed and supported depending on their performances. For e.g.

Heart- may need inotropic support if it fails to pump well

Lung – may need artificial ventilation support

Fluid collections in lung and peritoneal cavities may need drainage

Electrolyte imbalances – need to be corrected

Metabolic abnormalities – need corrections

Nutritional support- needed

Bleeding abnormalities will need good evaluation and corrections depending on the severity. Blood transfusion, platelet concentrates and fresh frozen plasma may be needed as deemed by the physician treating the case and not as routine. Steroids are not usually recommended in the treatment of dengue fever.

How can we avoid getting dengue illness?

Dengue fever is now considered the most important mosquito-borne viral disease in the world with increasing occurrences in Asia, Pacific Islands, Caribbean, South America and Africa. Within India in places like Kerala the weather conditions and water logging helps the mosquito to breed well, thereby increasing the number of mosquito borne diseases. 

Trying to reduce dengue can be done by the following ways:

1)      Mosquito control- mosquitoes can be controlled by killing them. This can be achieved by pyrethrin knock-down sprays or organophosphate sprays delivered in micro droplets.

2)      Prevent breeding of mosquitoes- unwanted containers should be discarded, buried or filled with sand, as water collecting in them provides good breeding grounds. Water potholes and unwanted water collecting sites should be filled in or destroyed.

3)      Killing the mosquito larvae- Larvae killing small fish or crustaceans called Mesocyclops can provide control of mosquito larvae.

4)      There are efforts being made to develop a dengue vaccine

5)      Research is being made to develop genetically modified mosquitoes to prevent the breeding of aedes mosquito

6)      Research is being done to produce antiviral therapies against the dengue virus

7)      Avoid mosquito bites by wearing protective clothing and appropriate repellents

8)      Cover all entry areas into the house by mosquito nets : this will prevent the mosquitoes from passing in

9)      Use electric bats to swat the mosquito that have entered the house and are likely to bite you while sleeping or resting

10)    Travelers who have returned from endemic areas or those with symptoms and signs mimicking dengue illness should be observed or even quarantined till cleared of the illness, 

(This original article by Dr Alexander+ is written and compiled in 'public interest’ to create public awareness about Dengue fever and not meant to replace physician evaluation and treatment++)

Additional resources

  www.cdc.gov/dengue