Dengue is a viral disease caused by four related but distinct dengue virus serotypes (DENV-1 to DENV-4). It spreads mainly through the bite of infected Aedes aegypti mosquitoes, prevalent in tropical and subtropical regions. The disease affects over half the world’s population, with an estimated 100–400 million infections annually.

Causes and Transmission

• Four dengue virus serotypes: DENV-1, DENV-2, DENV-3, DENV-4—all belonging to the Flavivirus genus.
• Mosquito vector: Primarily Aedes aegypti; these mosquitoes breed in small collections of stagnant water and bite during the day.
• No direct person-to-person spread, except rarely from mother to child during pregnancy.

Symptoms and Progression

• Typical onset: Symptoms appear 3 to 14 days after infection.
• Common symptoms: High fever, severe headache, joint/muscle pain (“breakbone fever”), nausea, vomiting, skin rash.
• Characteristic rash: Red patches, blanching on pressure—may progress to “islands of white in a sea of red” as fever subsides.
• Severe cases: About 1 in 20 develop severe dengue, with plasma leakage, bleeding, shock, and risk of death without prompt care.
• Recovery period: Symptoms typically last 2 to 7 days.

Risk Factors and Disease Severity

• Antibody-dependent enhancement (ADE): Prior infection with a different dengue serotype increases risk for severe disease.
• Higher risk groups: Children, elderly, people with pre-existing conditions.
• DENV-2 often causes severe disease, while DENV-1 was most prevalent in some recent studies.

Prevention and Control

• Mosquito control: Eliminate standing water, use repellents, window screens, wear protective clothing.
• Vaccines: Dengvaxia (for those previously infected), Qdenga (for ages ≥4, regardless of prior infection).
• Biological controls: Wolbachia-infected mosquitoes are used to block virus transmission.
• Public health campaigns: Remove mosquito breeding sites, educate communities.

Global Trends and Impact

• Endemic in 100+ countries: Most common in Southeast Asia, Americas, Africa, Western Pacific.
• Rapid expansion: Urbanization and climate change push dengue into new regions—including parts of Europe and the US.
• Incidence rises: 30-fold increase over 50 years; 5+ million reported cases and 5,000 deaths globally in 2023.
• WHO: Dengue is listed among the world’s top ten global health threats.

Wolbachia method

• The Wolbachia method uses a naturally occurring bacterium, Wolbachia, to control mosquito-borne diseases like dengue, Zika, and chikungunya.
• Wolbachia is introduced into Aedes aegypti mosquitoes, making them less able to transmit viruses to people.

How Wolbachia Works

• Blocks virus replication inside the mosquito so dengue and related viruses can''t reach levels needed for transmission.
• Does not harm the mosquito or humans; infected mosquitoes live normally but can''t pass viruses as easily.
• Wolbachia is inherited by offspring—females with the bacterium pass it on to future generations, allowing the effect to persist naturally.

Deployment Strategies

• Population replacement: Both male and female Wolbachia-infected mosquitoes are released. They breed with wild mosquitoes, spreading Wolbachia through the local population.
• Population suppression: Only male mosquitoes with Wolbachia are released. When they breed with wild females, the eggs don''t hatch, shrinking the mosquito population.

Impact and Effectiveness

• Major trials in places like Yogyakarta, Indonesia showed up to 77% reduction in dengue cases and up to 86% fewer hospitalizations where Wolbachia mosquitoes established.
• Singapore''s suppression program led to up to 98% reduction in Aedes aegypti numbers and fewer dengue cases in treated zones.
• The method is eco-friendly—there is no widespread impact on local wildlife or food chains.

Safety and Sustainability

• Wolbachia is common in nature, found in around 50% of insect species.
• No known risk to humans, animals, or the wider environment; regulatory assessments in multiple countries have deemed it safe.
• Self-sustaining: Once established, Wolbachia populations persist with little or no ongoing intervention.
• Does NOT require pesticides or chemicals, reducing dependence on traditional mosquito control methods.

Limitations and Future Directions

• The method does not completely eliminate dengue, but it offers a sustainable way to drastically reduce outbreaks and protect communities.
• Ongoing research aims to optimize deployment and adapt the strategy for more regions and vector-borne diseases.
• The World Mosquito Program (WMP) and other organizations are expanding the method globally with strong community engagement and promising results.

Dengue Immunity and Vaccine Development (Recent Developments)

The specific components of the immune response that protect against dengue virus (DENV) infection are not well understood. A novel study provides insights into developing strong immunity against DENV, which has implications for vaccine development.

Key Findings of the Study

• Envelope Dimer Epitope (EDE)-like Antibodies:
• EDE-like antibodies have been identified as key for building broad, cross-serotype immunity following natural infection or vaccination.
• The study found that EDE-like antibodies were prevalent in children with secondary DENV immunity, with 81.8% to 90.1% of participants having detectable levels.
• Antibody-Dependent Enhancement:
• Primary immunity from the first infection increases the risk of severe disease upon re-infection with a different serotype.
• This phenomenon poses a challenge for developing dengue vaccines, leading to the recommendation that vaccines be administered only to those with prior exposure.
• Role of EDE-like Antibodies:
• The study suggests these antibodies are a hallmark of established immunity against dengue.
• Higher levels of EDE-like antibodies were associated with lower odds of symptomatic dengue and hospitalization, highlighting their protective effect.

Dengue Vaccine Challenges and Current Solutions

• Current Vaccines:
• The two primary vaccines are Dengvaxia and QDENGA.
• These vaccines are most effective in individuals who have had at least one prior dengue infection.
• Study Limitations and Future Directions:
• The study had limitations, like a small number of cases for assessing protection against all serotypes.
• Further research is necessary to validate EDE-like antibodies as indicators of protection, which could guide vaccine efficacy trials.

The study marks a significant advance in understanding dengue immunity, offering potential pathways to more effective vaccines by focusing on eliciting high levels of EDE-like antibodies.

UPSC PRELIMS PYQs

UPSC Prelims 2014

Question: Which of the following diseases are transmitted by mosquito?

1. Dengue
2. Malaria
3. Filariasis
4. Typhoid

Select the correct answer using the code given below:

(a) 1, 2 and 3 only

(b) 1 and 3 only

(c) 2 and 4 only

(d) 1, 2, 3 and 4
Answer: (a) 1, 2 and 3 only

UPSC Prelims 2017

Question: Consider the following statements:

1. In tropical regions, Zika virus disease is transmitted by the same mosquito that transmits dengue.
2. Sexual transmission of Zika virus disease is possible.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2
Answer: (c) Both 1 and 2

UPSC Prelims 2020

Question: With reference to diseases transmitted by mosquitoes, consider the following pairs:

          Disease — Type of Virus

1. Dengue — Flavivirus
2. Chikungunya — Alphavirus
3. Zika — Flavivirus

Which of the pairs given above are correctly matched?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) All of the above

Answer: (d) All of the above

UPSC Prelims 2023  

‘Wolbachia method’ is sometimes talked about with reference to which one of the following?

(a) Controlling the viral diseases spread by mosquitoes

(b) Converting crop residues into packing material

(c) Producing biodegradable plastics

(d) Producing biochar from thermo-chemical conversion of biomass

Answer: (a) Controlling the viral diseases spread by mosquitoes