Diseases

Dengue : Causes, Pathogenesis, Symptoms, Diagnosis, Treatment & Prevention

Dengue : Causes, Pathogenesis, Symptoms, Diagnosis, Treatment & Prevention :

Definition :

  • Dengue is a febrile illness exhibiting Fever with haemorrhages.
  • Dengue is caused by virus- Flavivirus – transmitted by mosquitoes principally Aedes aegypti .
  • Causing agent – Flavivirus
  • Vector – Aedes aegypti
  • Aedes aegypti breeds in standing water; collections of water in containers, water-based air coolers and tyre dumps are a good environment for the vector in large cities.

Types:  

Dengue occurs in following forms :-
1. Dengue fever / Break bone fever

  • Dengue fever or break-bone fever in an uncomplicated way is a self-limited febrile illness affecting muscles and joints with severe back pain due to myalgia.

2. Dengue Haemorrhagic fever / DHF

  • DHF is a severe and potentially fatal form of acute febrile illness characterised by cutaneous and intestinal haemorrhages due to thrombocytopenia, haemoconcentration, hypovolaemic shock and neurologic disturbances.
  • DHF is most common in children under 15 years of age.

3. Dengue Shock Syndrome / DSS

  • If Dengue fever remains untreated, Dengue shock syndrome (DSS) develops & death occurs.

Pathogenesis :

  • Dengue virus infects blood monocytes, lymphocytes and endothelial cells. This initiates complement activation and consumptive coagulopathy including thrombocytopenia.
  • The entire process takes place rapidly and may evolve over a period of a few hours.
  • If patient is treated appropriately at this stage, there is rapid and dramatic recovery.
  • But in untreated cases, dengue shock syndrome develops and death occurs

Clinical Symptoms :

  • Incubation period : 2 to 7 days
  • Asymptomatic infections are common, particularly in children, but the disease is more severe in infants and the elderly.
  • The initial febrile phase is frequently followed by a rash as the fever settles.
    • Laboratory findings include leucopenia, neutropenia, thrombocytopenia and elevated alanine aminotransferase (ALT) or aspartate aminotransferase (AST).
    • Prodrome : 2 days of Malaise and Headache
  • Thus, Dengue is characterised by following symptoms :
    • Fever
    • Rash
    • Convalescence
    • Backache
    • Arthralgias
    • Headache
    • Generalised pains(‘break-bone fever’)
    • Pain on eye movement
    • Lacrimation
    • Scleral injection
    • Anorexia
    • Nausea
    • Vomiting
    • Pharyngitis
    • Upper respiratory tract symptoms
    • Relative bradycardia
    • Prostration
    • Depression
    • Hyperaesthesia
    • Dysgeusia
    • Lymphadenopathy
  • Many symptomatic infections run an uncomplicated course, but complications or a protracted convalescence may ensue.

Complications :

  • If Dengue fever remains untreated, a Critical Phase is obtained 3-7 days after onset of fever.
  • Occurance of Critical Phase leads into following complications :
    – Dengue haemorrhagic fever and disseminated intravascular coagulation
    – Dengue shock syndrome
    – Hepatitis, cerebral haemorrhage or oedema, encephalitis, cranial nerve palsies, rhabdomyolysis, myocarditis.
    – Vertical transmission if infection within 5 weeks of delivery .

Diagnosis : 

Dengue virus can be detected by following methods :-
1. Virus isolation
2. Nucleic acid detection: Nucleic acid can be detected by following methods :-

  • Reverse transcriptase-polymerase chain reaction (RT-PCR)
  • Real-time PCR
  • Nucleic acid sequence based Amplification

3. Antigen detection
4. Serological tests: Following serological tests can be performed :-

  • ELISA (Enzyme-linked immunosorbent assay)
    – MAC-ELISA ( IgM antibody-capture ELISA )
    – IgG ELISA
    – Anti-dengue virus IgA capture ELISA (AAC-ELISA)
  • IgM/IgG ratio
  • Haemagglutination-inhibition (HI) test
  • Haematological tests

5. Tourniquet test:

  • It determines Capillary fragility.

Treatment :

  • There is no specific medicine / antibiotic to treat dengue infection. No existing antivirals are effective.
  • Treatment is supportive, emphasising fluid replacement and appropriate management of shock and organ dysfunction.
    – If you are suffering from Dengue fever, you should use NSAIDs like- Paracetamol.
    – Aspirin should be avoided due to bleeding risk.
    – Corticosteroids have not been shown to help.
    – You should also rest, drink plenty of fluids, and see your doctor.
    – If you start to feel worse in the first 24 hours after your fever goes down, you should get to a hospital immediately to be checked for complications.

Prevention :

  • There is no licensed vaccine available.
  • Thus, the best way to prevent the disease is to prevent bites by infected mosquitoes, particularly if you are living in or traveling to a tropical area.
  • To protect yourself:
    – Stay away from heavily populated residential areas, if possible.
    – Use mosquito repellents, even indoors.
    – When outdoors, wear long-sleeved shirts and long pants tucked into socks.
    – When indoors, use air conditioning if available.
    – Make sure window and door screens are secure and free of holes.
    – If sleeping areas are not screened or air conditioned, use mosquito nets.
    – If you have symptoms of dengue, speak to your doctor.
  • Breeding places of Aedes mosquitoes should be abolished and the adults destroyed by insecticides.

WHO-proposed clinical definition of dengue

  • Probable dengue

– Exposure in an endemic area
– Fever

Two of:

1. Nausea/vomiting
2. Rash
3. Aches/pains
4. Positive tourniquet test
5. Leucopenia
6. Any warning sign

•Laboratory confirmation important
•Needs regular medical observation and instruction in the warning signs
•If there are no warning signs, need for hospitalisation is influenced by age, comorbidities, pregnancy and social factors

  • Dengue with warning signs– Probable dengue plus one of:
    1. Abdominal pain or tenderness
    2. Persistent vomiting
    3. Signs of fluid accumulation, e.g. pleural effusion or ascites
    4. Mucosal bleed
    5. Lethargy
    6. Hepatomegaly > 2 cm
    7. Rapid increase in haematocrit with fall in platelet count

               •Needs medical intervention, e.g. intravenous fluid.

  • Severe dengue– Severe plasma leakage leading to:
    1. Shock (dengue shock syndrome)
    2. Fluid accumulation with respiratory distress
    – Severe haemorrhagic manifestations, e.g. GI haemorrhage
    – Severe organ involvement:
    1. Liver AST or ALT ≥ 1000 U/L
    2. CNS: impaired consciousness
    3. Cardiomyopathy
    4. Other organs, e.g. renal impairment

               •Needs emergency medical treatment and specialist care with intensive care input.
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