Explained: Key factors behind spike in dengue

Dengue: The national capital has witnessed a sudden surge in vector-borne diseases, with the total number of dengue cases standing at 1,229 to date this year. This figure includes a significant increase over the last week, with over 300 new cases reported, indicating a slow but steady rise in mosquito-borne diseases across the city.

Although there’s been an uptick in cases recently, the total number for 2024 so far is lower compared to previous years. For instance, by the same period last year, Delhi had seen 3,013 cases, suggesting that while dengue is present and increasing, the overall incidence might be lower this year due to various preventive measures or environmental factors.

Alongside dengue, there has been an increase in malaria cases, with 363 cases reported by September 2024, up from 294 in the same period of 2023. Chikungunya cases, while fewer, have also doubled from last year, reaching 43 cases.

Also read: How to stay healthy this monsoon: An expert shares diet tips

What is dengue?

Dengue is a mosquito-borne viral illness caused by the dengue virus (DENV), which belongs to the Flavivirus family. There are four distinct serotypes of the dengue virus: DENV-1, DENV-2, DENV-3, and DENV-4. An individual infected with one serotype acquires lifelong immunity to that particular type but can still be infected by the other serotypes. Successive infections increase the risk of developing severe dengue.

How dengue spreads

Dengue is primarily transmitted through the bite of infected female Aedes mosquitoes, mainly Aedes aegypti and, to a lesser extent, Aedes albopictus. These mosquitoes are most active during the day, with peak biting periods early in the morning and before dusk. The virus enters the mosquito when it bites an infected person, and after an incubation period in the mosquito (8–12 days), it can be transmitted to other humans.

The spread of dengue occurs in areas with inadequate water storage systems and poor waste management, leading to the accumulation of stagnant water, which serves as breeding grounds for mosquitoes. Urbanisation and rapid population growth have exacerbated the spread of dengue in many parts of the world, especially in Southeast Asia, Latin America, and Africa.

Human-to-mosquito transmission

Dr Ritu Saxena, Deputy Medical Superintendent and Head of the Department of Accident and Emergency at Lok Nayak Hospital, explained, “Mosquitoes can become infected by biting individuals who have the dengue virus in their bloodstream, known as viremic. This includes people with symptomatic dengue, those who have not yet developed symptoms (pre-symptomatic), and individuals who remain asymptomatic throughout the infection.”

“Human-to-mosquito transmission can occur up to two days before the onset of symptoms and up to two days after the fever subsides. The risk of mosquitoes becoming infected increases with high levels of viraemia (viral load) and fever in the person. In contrast, higher levels of dengue-specific antibodies in the person are linked to a reduced risk of mosquito infection. Typically, viraemia lasts for 4–5 days, though it can extend up to 12 days in some cases,” Dr Saxena added.

Symptoms of dengue

Dengue manifests in a range of symptoms, varying from mild to severe. The incubation period after a mosquito bite is typically 4 to 10 days, after which the symptoms begin to appear.

Mild dengue fever

In mild cases, dengue presents flu-like symptoms, which may include:

• High fever (up to 40°C or 104°F)
• Severe headaches
• Pain behind the eyes
• Joint and muscle pain (often referred to as “breakbone fever”)
• Fatigue
• Nausea and vomiting
• Skin rash, which may appear 2–5 days after the onset of fever

These symptoms usually last for 2–7 days, and most individuals recover without the need for hospitalisation.

Severe dengue (Dengue Haemorrhagic Fever and Dengue Shock Syndrome)

Severe dengue is a more serious form of the disease and can be life-threatening. It is characterised by plasma leakage, fluid accumulation, severe bleeding, and organ impairment. Warning signs of severe dengue typically appear 3–7 days after the onset of symptoms, coinciding with a drop in fever, and include:

• Severe abdominal pain
• Persistent vomiting
• Rapid breathing
• Bleeding gums or nose
• Fatigue and restlessness
• Blood in vomit or stool

Severe dengue can lead to Dengue Haemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS), both of which require immediate medical attention. If not treated in time, these conditions can result in death.

Diagnosis of Dengue

Dengue is diagnosed based on clinical symptoms, patient history, and laboratory tests. Early detection is essential to prevent complications, especially in areas where dengue is endemic.

Blood Tests

Blood tests are commonly used to confirm dengue. These include:

• NS1 Antigen Test: Detects the presence of the virus during the early stages of infection.
• PCR (Polymerase Chain Reaction): Used to detect viral RNA in the blood.
• ELISA (Enzyme-Linked Immunosorbent Assay): Helps identify antibodies produced in response to the dengue virus.

It is important to note that diagnostic tests may sometimes produce false-negative or false-positive results, particularly in areas where multiple types of mosquito-borne diseases are present, such as malaria or chikungunya.

Treatment for dengue

There is no specific antiviral treatment for dengue. Supportive care is the mainstay of treatment, focusing on managing symptoms and preventing complications.

Mild dengue

For mild cases, home care is often sufficient. Treatment includes:

• Hydration: Drinking plenty of fluids (oral rehydration solution, juices, water) to prevent dehydration is crucial, as fever and vomiting can lead to significant fluid loss.
• Pain Relief: Over-the-counter medications like paracetamol (acetaminophen) can be used to manage pain and reduce fever. It is important to avoid nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and aspirin, as these can increase the risk of bleeding.

Severe dengue

Severe cases require hospitalisation and close monitoring to prevent complications. Treatment for severe dengue includes:

• Intravenous Fluids (IV): Administered to maintain fluid balance and treat dehydration caused by plasma leakage.
• Blood Transfusion: In cases of severe bleeding, blood transfusions may be necessary to replace lost blood.
• Monitoring: Patients are continuously monitored for signs of organ dysfunction, shock, or other life-threatening complications.

Early detection and access to proper medical care lower the fatality rate of severe dengue to less than 1%.

Prevention of dengue

Given that there is no specific treatment for dengue and no widely available vaccine for all individuals, prevention is key to controlling the spread of the disease. Preventive measures focus on reducing mosquito populations and protecting individuals from mosquito bites.

Also read: World lung day: 7 effective ways to quit smoking

Mosquito control

Eliminating Breeding Sites: Removing stagnant water, where mosquitoes lay eggs, is critical in reducing mosquito populations. This includes:

• Covering water storage containers.
• Regularly cleaning and emptying water-filled pots, flower vases, and buckets.
• Proper waste disposal to prevent the accumulation of discarded items that can collect water.

Insecticides and Larvicides: Spraying insecticides in areas where mosquitoes breed can help control the mosquito population. Larvicides, which kill mosquito larvae, can be applied to water bodies that cannot be drained.

Biological Control: Introducing natural mosquito predators, such as fish (e.g., Gambusia) and bacteria (Wolbachia), that infect mosquitoes and reduce their ability to transmit the virus are other methods of mosquito control.

Personal Protection

• Use of Mosquito Nets: Sleeping under mosquito nets, especially during the day, is an effective way to avoid bites.
• Repellents: Applying insect repellent containing DEET, picaridin, or oil of lemon eucalyptus on exposed skin helps keep mosquitoes at bay.
• Protective Clothing: Wearing long sleeves, long trousers, and shoes can reduce the area of exposed skin, lowering the chances of being bitten.

Fogging is useless

Dr Saxena commented, “The fogging done by the civic authorities in order to kill the dengue mosquito is useless and can prove to be more harmful. To escape the fogging, the mosquitoes enter houses, resulting in more mosquito bites and spreading the disease.”

“On the other hand, the chemical used in fogging, which includes pyrethrum, malathion, and diesel, can make uncovered food poisonous. Instead of fogging, the agencies should adopt other measures to control mosquito breeding, such as Gambusia fish and pouring diesel on stagnant water to curb breeding,” Dr Saxena added.

Vaccination against dengue

A vaccine, Dengvaxia, is available in some countries and offers protection against all four serotypes of the dengue virus. However, it is recommended only for individuals who have had a previous dengue infection, as there is an increased risk of severe dengue for first-time infections after vaccination. Research is ongoing to develop a more universally effective dengue vaccine.

Notably, this vaccine is not available in India so far.

In conclusion, dengue is a serious mosquito-borne viral disease that poses a growing global threat, particularly in tropical and subtropical regions. Understanding the disease’s transmission, symptoms, and prevention measures is critical in reducing its spread. While there is no specific cure for dengue, early detection, proper medical care, and prevention strategies can save lives and mitigate the disease’s impact.