# Dengue Virus

> Dengue virus for MBBS Microbiology: flavivirus serotypes, Aedes aegypti, antibody-dependent enhancement, severe dengue, NS1 and IgM diagnosis.

- Canonical URL: https://prepelephant.com/topics/mbbs/microbiology/dengue-virus
- Exam / course: MBBS · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Dengue Virus", PrepElephant, https://prepelephant.com/topics/mbbs/microbiology/dengue-virus

## Direct answer

Dengue virus is a single-stranded ribonucleic acid flavivirus with four serotypes, DEN-1 to DEN-4, transmitted by the day-biting Aedes aegypti mosquito breeding in domestic water containers. One serotype confers lifelong homotypic immunity only, and a second infection can trigger antibody-dependent enhancement, producing severe dengue with plasma leakage, haemoconcentration, haemorrhage and shock around the time fever settles. Management is meticulous fluid balance — there is no specific antiviral — with paracetamol alone for fever.

## What you must remember

- **Virus and vector:** four serotypes circulate in India, transmitted mainly by Aedes aegypti, a day-biting peri-domestic mosquito breeding in clean stagnant water in containers; humans are the main amplifying host.
- **Antibody-dependent enhancement:** non-neutralising antibody from a first infection eases entry of a second serotype into Fc-receptor-bearing monocytes, which is why secondary dengue is severer.
- **Clinical features:** sudden high fever with severe headache, retro-orbital pain, myalgia and arthralgia — breakbone fever — with rash and a positive tourniquet test.
- **Warning signs:** abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy, tender hepatomegaly and rising haematocrit with falling platelets — these demand admission.
- **Severe dengue:** plasma leakage with pleural effusion and ascites, haemoconcentration, severe thrombocytopenia, significant bleeding and dengue shock syndrome, with the critical phase around defervescence on days three to seven.
- **Diagnosis:** the NS1 antigen test is positive in the first days, immunoglobulin M appears after about five days, and a rapid high immunoglobulin G suggests secondary infection; polymerase chain reaction confirms when needed.
- **Management:** oral fluids with daily platelet and haematocrit monitoring for uncomplicated cases, careful intravenous crystalloids for the critical phase, avoidance of aspirin and non-steroidal anti-inflammatory drugs, and no routine platelet transfusion without significant bleeding.

## Common confusion

Dengue is equated with a low platelet count alone, but severity is defined by plasma leakage — the rising haematocrit is the more important number, showing haemoconcentration. Test timing is also confused: NS1 is early and immunoglobulins later, so negative serology on day two does not exclude dengue. Remember the vector's habits — Aedes bites by day and breeds in fresh water in and around houses, unlike night-biting anopheles and culex, so source reduction of containers is the control strategy.

## Exam-focused takeaway

In theory, describe the serotypes, vector and breeding habits, antibody-dependent enhancement, the phases of illness with warning signs, diagnosis by NS1 and serology, and fluid-based management — mirroring national guidelines scores well. In viva, expect why second infections are worse, when the critical phase occurs and why aspirin is avoided. At the practical, interpreting a dengue panel with platelet and haematocrit trends is standard.

## Frequently asked questions

### Why is secondary dengue more severe?

Antibody to one serotype enhances infection by another through antibody-dependent enhancement, raising viral load and driving the plasma leakage of severe dengue.

### Which mosquito transmits dengue?

Mainly Aedes aegypti, day-biting and breeding in clean water in domestic containers such as coolers, tyres and tanks, making source reduction the key control measure.

### What are the warning signs demanding admission?

Abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy, tender hepatomegaly and a rising haematocrit with falling platelets.

### Which tests diagnose dengue and when?

NS1 antigen in the first days, immunoglobulin M from about the fifth day and high immunoglobulin G in secondary infection; polymerase chain reaction confirms when available.

### Why is haematocrit monitored so closely?

A rising haematocrit signals haemoconcentration from plasma leakage, the hallmark of severe dengue, and guides fluid replacement in the critical phase.

### Is there specific treatment or a vaccine?

Treatment is supportive with fluids and paracetamol; a live vaccine is used selectively in highly endemic settings, so vector control remains the main tool.