Dengue is a mosquito-borne viral disease caused by Dengue virus. Incidence of dengue has grown rapidly in recent years all over the world and as of summer 2019, it has caused an outbreak in Nepal.
What is Dengue?
‘Dengue’ is a West Indian Spanish word derived from Ki Swahili ‘ka dinga pepo‘(a kind of cramping plague’); “dinga” meaning ‘fever with haemorrhage.’
In the British West Indies it was called ‘dandy fever‘ (due to the stiff posture of its victims), and in Cuba dengue was later termed ‘quebranta huesos‘ or ‘break-bone fever‘(due to severe myalgias and arthralgias).
It is a benign syndrome caused by an arboviral infection, characterized by biphasic fever, myalgia, or arthralgia, rash (maculopapular/rubelliform), leukopenia and thrombocytopenia.
•The epidemiology of dengue exhibits a complex relationship among:
- Human beings
• Agent/virus (Flaviviridae)
• The environment (Hot and humid climate)
Characteristics of Dengue Virus
•Flavivirus (Flavivirus is a genus of viruses in the family Flaviviridae. )
•Single-stranded RNA virus
•40 to 50 nanometers
Types of Dengue Viruses:
There are 4 sub-serotypes :
(DENV-1, DENV-2, DENV-3, and DENV-4)
** Infection with one serotype elicits immunity to that serotype but does not provide long-term cross-protective immunity to the remaining serotypes.**
Vectors / Agent for transmission:
- Aedes aegypti (found mainly in the urban area)
- Aedes albopictus (found mainly in peripheral areas)
** Aedes aegypti is a principal vector, which bites in day time **
- Also Known as Tiger mosquitoes (distinguished by white stripes on black body).
- Female mosquito acts as a vector.
- They are most abundant during the rainy season (monsoon and post-monsoon).
- They do not fly over a long distance- <100mts(110yards), this factor facilitates its eradication.
Breeding place of Aedes mosquito.
- In mostly found in tropical areas and A. aegypti is highly urbanized.
- They breed in fresh/artificial stagnant water –e.g. water stored for drinking or bathing and in rainwater collected in any container or any water trapped in vegetations.
Mode of transmission
It is transmitted from mosquito to human from the bite of infected female Aedes mosquito. When a mosquito bites a person with dengue it gets infected and further bite from this mosquito spreads the disease.
Pathophysiology of Dengue Syndrome
The immune mechanism for protection against or contribution to severe disease still remains controversial.
Various mechanisms of severe disease have been suggested, including
1. Antibody-dependent enhancements
2.Complement activation by virus- antibody complex
Clinical manifestation of Dengue:
Many patients infected with dengue virus remain asymptomatic.
Others, after an incubation period of 4-7 (range 3-14) days, develop a febrile illness.
The manifestations of which are similar and overlapping in nature grouped into ‘Dengue Syndromes‘.
It encompasses the following: §
1. Undifferentiated fever
4.Expanded dengue syndrome (rare)
The Natural Course of illness of Dengue:
–Majority of dengue virus infections are asymptomatic.
–Age & sex appears to influence the prevalence of the symptomatic disease.
–Majority of infections in children under age 15 years are asymptomatic or minimally symptomatic.
i. Undifferentiated fever
- Occurs in primary dengue infection,
- May develop a simple fever indistinguishable from other viral infections.
- Maculopapular rashes may accompany the fever or may appear during defervescence.
- Upper respiratory and gastrointestinal symptoms are common.
ii. Dengue fever:
- Typically, the onset of DF is sudden with a sharp rise in temperature. It is frequently associated with a flushed face and headache.
- Retro-orbital pain on eye movement or eye pressure
- Backache, and
- Pain in the muscles and joints/bones.
- The other common symptoms include anorexia and dysgeusia, constipation, colicky pain and abdominal tenderness
- The body temperature is usually between 39 ° C to 40 °C (102° F to 104° F)
- Fever may be biphasic, lasting 2–7 days in the majority of cases.
- First 2 to 3 days
Diffuse flushing or fleeting eruptions may be seen on the face, neck and chest.
- From 3rd and 4th day
There may be maculopapular or rubelliform rash.
Skin itching may also be observed.
1. It is quite rare in DF, but petechiae may be present.
2. Tourniquet test is positive in this case.
iii. Dengue Hemorrhagic Fever (DHF):
The clinical course of illness passes through the following three phases:
- Febrile Phase: similar to DF.
- Critical Phase:
• DF/DHF goes to critical phase after 3-4 days of onset of fever.
• Plasma leakage (persists for 36-48 hrs) is the hallmark of the critical phase.
• High haemoconcentration are documented
• Patients may develop hypotension.
• Abnormal haemostasis and leakage of plasma lead to shock, bleeding, accumulation of fluid in the pleural and abdominal cavity.
• Commonly in DHF, platelet count is less than 100000 per/cumm of blood.
- Convalescent Phase:
• This phase usually after 6-7 days of fever and last for 2-3 days.
• During this phase, the extracellular fluid which was lost due to capillary leakage returns to the circulatory system.
• Signs and symptoms improve.
iv. Dengue Shock Syndrome (DSS):
- Dengue Shock Syndrome is a presentation of Dengue Syndromes when there are criteria of DHF plus signs of circulatory failure, manifested by :
•Rapid and weak pulse
•Narrow pulse pressure (≤ to 20 mm Hg)
•Hypotension for age
•Cold clammy skin
•Undetectable pulse and blood pressure
v. Expanded dengue syndrome/Isolated organopathy (unusual manifestations):
- Patients with dengue illness can sometimes develop unusual manifestations such as – involvement of liver, kidneys, brain or heart with or without evidence of fluid leakage.
- Therefore this do not necessarily fall into the category of DHF.
- These conditions are very rare and management is symptomatic.
Classification of dengue based on the severity
Categorisation of patient based on severity:
- These are patients who are dengue patients without a warning sign.
- They may be sent home.
- These include patients with warning signs.
- These are patients who should be admitted for in-hospital management (as they approach the critical phase)
- These are patients with severe dengue who require emergency treatment and urgent referral because they are in the critical phase of the disease.
- Arboviruses: Chikungunya virus
- Other viral diseases: Measles; rubella and other viral exanthems; Epstein- Barr Virus (EBV); Enteroviruses; Influenza; hepatitis A; Hantavirus.
- Bacterial diseases: Meningococcaemia, leptospirosis, typhoid, melioidosis, rickettsial diseases, scarlet fever, sepsis
- Parasitic diseases: Malaria.
Lab test for diagnosis and monitoring:
Including Total Leucocyte Count, Total Platelet Count and Haematocrit should be done on the first consultation of the patient to have the baseline :
– All febrile patients at the first visit.
– All patients with warning signs.
- Leucopenia: WBC count <5000/cu mm. Seen in DF and DHF both.
- Thrombocytopenia: Platelet count < 1lacs/cu mm.
- Haematocrit: >20%
2) Biochemical Tests:
Serum AST(SGOT) and ALT (SGPT):
- AST and ALT levels are frequently elevated in both adults and children with DF and DHF;
- Usually 5 to 15 times the upper limit of normal in patients with DHF.
- Commonly AST is more than ALT in these cases.
•In Special Cases:
- Hypoproteinemia/Hypoalbuminaemia (as a consequence of plasma leakage).
- Hyponatremia is frequently observed in DHF and is more severe in shock.
- Hypocalcemia (corrected for hypoalbuminemia) has been observed in DHF.
- Metabolic acidosis is frequently found in cases with prolonged shock.
- Blood urea nitrogen is elevated in prolonged shock.
3) Coagulation Profile:
- Assays of coagulation and fibrinolytic factors show a reduction in DSS cases.
- Partial thromboplastin time and prothrombin time are prolonged in about half and one-third of DHF cases respectively.
- Thrombin time is also prolonged in severe cases.
4) Other tests:
- Urine R/M/E: Albuminuria
- Stool test: Occult blood is often found in the stool.
- Chest X-Ray or Ultrasonography: For Detection of pleural effusions or ascites.
Management and Prevention Of Dengue Will be discussed in Part Two of this post
This post is written By Dr Ranjan Saraf find the full presentation at
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