DENGUE FEVER: PANICS ASIDE BUT KNOW AND WATCH OUT

Dengue fever or dengue is a disease caused by mosquitoes due to an infection of a virus of the family Flaviviridae. More common in tropical and subtropical regions. There are 4 types of dengue viruses named as DENV-1, DENV-2, DENV-3 and DENV-4. Transmitted by bites from Aedes aegypti and Aedes albopictus mosquito species.

About dengue virus

  • Belongs to a group of flaviviruses.
  • It contain a single stranded, non-segmented RNA viruses as genetic material
  • There are 4 types of dengue viruses named as DENV-1, DENV-2, DENV-3 and DENV-4.
  • Infection with serotype gives lifelong immunity to that particular serotype but secondary infection with another serotype can cause severe dengue (dengue shock syndrome-DSS).

Signs and Symptoms of dengue fever

Incubation period is about 4-10 days. Symptoms usually last for about 2-7 days. Many people will be asymptomatic, 1 in 4 with dengue becomes symptomatic. Commonly presented as mild to moderate, non-specific acute febrile illness. There are 3 phases they are:

1. Febrile phase: 

  • High grade fever that lasts for about 2-7 days in addition to severe headaches and retro orbital pain, severe joint pains and/or muscle pain, bone pain, macular or maculopapular rashes. 
  • Patient may present with nausea and vomiting, petechiae, purpura, bleeding gums, epistaxis and haematuria and a positive tourniquet test (most of them not all). 
  • Anorexia, loss of appetite, sore throat, altered taste sensation and lymphadenopathy may also be observed.
  • At a later stage of this phase, the fever starts to drop – defervescence, which is due to the cessation of viremia. Some may also show warning signs (Persistent vomiting, severe abdominal pain, fluid accumulation in spaces like pleural cavity, mucosal bleeding, breathing difficulty, restlessness, hepatomegaly, progressive increase in hematocrit) that it is progressing into DSS at this time.
What is a tourniquet test?

Performed by inflating a blood pressure cuff around the upper arm to a midway between systolic and diastolic BP for 5 mins and after removing the cuff the number of petechiae per square inch is calculated. More than 20 : test is positive

2. Critical phase:

  • Begins after defervescence and usually lasts for about 24-48 hrs.
  • Most of them clinically improve during this period.
  • However some patients with considerable plasma leakage can develop severe dengue within few hours.
  • Reappearance of fever known as saddleback fever.
  • Increased vascular permeability is the cause of plasma leakage which causes a drop in blood volume that results in hypovolemic shock.
  • Patient may have conditions like pleural effusions, ascites due to plasma leakage.
  • Hypotension, tachycardia, tachypnea, decreased level of consciousness and hemoconcentration due to decreased blood volume.
  • In addition to this they also show severe haemorrhagic manifestations like hematemesis, GI bleeding, haematuria.

3. Convalescent or recovery phase:

  • In this phase, blood volume tend to stabilise by reabsorption of extravasated fluid into bloodstream.
  • Haemodynamic status stabilises.
  • WBC and platelet count starts to increase.

PATHOGENESIS IN BRIEF

When a female Aedes mosquito, the infected one, bites a person. 3 main organ systems are affected. They are immune system, liver and endothelial lining of blood vessels. What happens in dengue fever is that:

  • During a mosquito bite the virus enters and infects the immature dendritic cells in the skin.
  • These infected dendritic cells reach the lymph nodes and at the lymph nodes monocytes and macrophages are recruited to fight the infection but they are also infected by virus.
  • When monocytes and macrophages are infected they secrete large amount of cytokines into bloodstream that mediates the early non-specific symptoms of the infection. 
  • Also when these cells are affected they are unable to hold the viral replication which leads to increase in the viral load, and these host monocytes and macrophages undergo apoptosis.
  • Dissemination of virus through the bloodstream and reach vital organs including liver and bone marrow.
  • Direct destructive action on bone marrow precursor cells causes thrombocytopenia and leukopenia.
  • Elevated SGOT/SGPT observed in blood due to hepatocyte damage.
  • Due to endothelial cell damage and thrombocytopenia causes minor haemorrhagic manifestations.

How to diagnose dengue fever?

  • Blood test- leukopenia count decreases
  • Decreased platelet count
  • Nucleic acid amplification tests (NAATs)
  • Detection of NS1 antigen by immunoassays within 1 week of symptom onset.
  • Screen for antibodies, IgM

Treatment

 No specific anti-viral but only supportive treatment is available for dengue fever.

  • Drink lots of water to prevent dehydration due to all that fluid loss at the time of vomiting.
  • Pinch your skin if it is returning back to normal almost at the same time as you leave then its ok but if it is taking time to return back to normal or staying at the pinched state itself then you are dehydrated.
  • Check your urine colour consistently. It must be pale yellow. 
  • Paracetamol for fever with high temperature.
  • Avoid NSAIDs as it may cause bleeding risk.
  • Avoid mosquito bites to prevent the transmission.
  • Patients with coagulopathy fresh frozen plasma is given.
  • Consuming fruits can be good, especially papaya, pomegranate.

Written by Gayathri Gopinadh

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