Every monsoon, the arrival of heavy rains brings not only a refreshing respite from the scorching heat but also a host of health challenges. Among these, the resurgence of dengue fever is a significant concern. Dengue, a mosquito-borne viral infection, sees a drastic increase in cases during the monsoon season due to the ideal breeding conditions for the Aedes aegypti mosquito, which transmits the virus.

SYMPTOMS

Most people with dengue experience mild or no symptoms and recover within 1–2 weeks, though in rare cases, dengue can become severe and even fatal. If symptoms do occur, they typically begin 4–10 days after infection and last for 2–7 days. These symptoms can include a high fever (40 degrees Celsius or 104 degrees Fahrenheit), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands, and a rash. Individuals infected for a second time are at a higher risk of developing severe dengue. Severe symptoms often emerge after the fever subsides and may include severe abdominal pain, persistent vomiting, rapid breathing, bleeding from the gums or nose, fatigue, restlessness, blood in vomit or stool, intense thirst, pale and cold skin, and a feeling of weakness. It is crucial for individuals displaying these severe symptoms to seek immediate medical care. Post-recovery, individuals who have had dengue may feel fatigued for several weeks.

CASES IN INDIA

The total number of positive dengue cases in Karnataka has surpassed the 10,000 mark on Tuesday, reaching 10,449 cases, with 358 active hospitalisations. The dengue death toll remains at eight. On Tuesday, at least 4,572 blood samples were tested for dengue across the state, yielding 487 new positive results and bringing the total number of samples tested to 78,489.

This year, Maharashtra reported 3,736 dengue cases compared to 3,164 cases and four deaths last year.

In the past two weeks in West Bengal, approximately 18 people in the West Burdwan district contracted dengue, with 12 cases in the Asansol Municipal Corporation area and three in the Durgapur Municipal Corporation area. Cases of dengue are on the rise in Kolkata too. About 3-5 cases per week were observed at the Charnock Hospital.

Kerala has seen a sharp increase in dengue cases, with 1,075 infections reported across the state in the last 10 days amidst heavy rainfall.

GLOBAL BURDEN

According to the World Health Organization (WHO), “the incidence of dengue has grown dramatically around the world in recent decades, with cases reported to WHO increasing from 505 430 cases in 2000 to 5.2 million in 2019. A vast majority of cases are asymptomatic or mild and self-managed, and hence the actual numbers of dengue cases are under-reported. Many cases are also misdiagnosed as other febrile illnesses. The highest number of dengue cases was recorded in 2023, affecting over 80 countries in all regions of WHO. Since the beginning of 2023 ongoing transmission, combined with an unexpected spike in dengue cases, resulted in a historic high of over 6.5 million cases and more than 7,300 dengue-related deaths reported.

Several factors are associated with the increasing risk of spread of the dengue epidemic: the changing distribution of the vectors (chiefly Aedes aegypti and Aedes albopictus mosquitoes), especially in previously dengue naïve countries; the consequences of El Niño phenomena in 2023 and climate change leading to increasing temperatures and high rainfall and humidity; fragile health systems in the midst of the Covid-19 pandemic; and political and financial instabilities in countries facing complex humanitarian crises and high population movements.”

TRANSMISSION

Transmission through mosquito bites:

The dengue virus is transmitted to humans through the bites of infected female mosquitoes, primarily the Aedes aegypti mosquito. While other species within the Aedes genus can also act as vectors, their contribution is generally secondary to Aedes aegypti. However, in 2023, there was a notable increase in local dengue transmission by Aedes albopictus (tiger mosquito) in Europe.

After a mosquito feeds on an infected person, the virus replicates in its midgut before spreading to secondary tissues, including the salivary glands. The period from virus ingestion to transmission to a new host is known as the extrinsic incubation period (EIP), which takes about 8–12 days when the ambient temperature is between 25–28 degrees Celsius. This period can vary based on factors such as daily temperature fluctuations, virus genotype and initial viral concentration. Once a mosquito becomes infectious, it can transmit the virus for the rest of its life.

Human-to-mosquito transmission:

Mosquitoes can become infected by biting people who are viremic with the dengue virus, including those with symptomatic infections, pre-symptomatic infections and asymptomatic carriers. Human-to-mosquito transmission can occur up to two days before the onset of symptoms and up to two days after the fever has resolved.

The risk of mosquito infection is higher in patients with high viremia and high fever, while high levels of DENV-specific antibodies are associated with a decreased risk of mosquito infection. Most people remain viremic for about 4–5 days, though viremia can last up to 12 days.

Maternal transmission:

Although the primary mode of dengue virus transmission involves mosquito vectors, there is evidence of possible maternal transmission (from a pregnant mother to her baby). Vertical transmission rates appear low, with the risk of transmission linked to the timing of the dengue infection during pregnancy. Pregnant women with dengue may face complications such as preterm birth, low birthweight and foetal distress.

Other transmission modes:

Rare cases of dengue transmission via blood products, organ donation, and transfusions have been recorded. Additionally, transovarial transmission of the virus within mosquitoes has also been documented.

DOCTORS’ ADVICE

Dr Debkishore Gupta, a specialist in infectious diseases, explained to The Statesman, “Last year, the DENV-3 serotype was behaving unusually, almost like a second-time dengue infection. Typically, if a person contracts dengue for a second time, the risk of complications is higher. However, individuals infected with DENV-3 for the first time were also experiencing severe complications, including a drop in platelets, which was atypical. Dengue can only infect a person four times, as there are four serotypes: DENV-1, DENV-2, DENV-3 and DENV-4. The second infection generally triggers an exaggerated immune response, leading to platelet loss, blood leakage and a drop in blood pressure, necessitating hospitalisation. Although it’s too early to determine the most prevalent serotype this year, early awareness is crucial. People with comorbidities and immunocompromised conditions are particularly vulnerable and can experience severe complications even with a first-time infection.”

When a person contracts both diseases simultaneously, significant risk factors are involved. Co-infection can result in severe symptoms, both additional and overlapping, and in many cases, it can exacerbate complications.

Dr Gupta further explained the risks of co-infection: “When a person contracts dengue along with another disease, such as malaria or a respiratory infection, the risk of severe symptoms increases significantly. Co-infection can exacerbate complications. We’ve observed that many dengue patients also contract other infectious diseases, sometimes even within hospital settings. It’s important to avoid antibiotics in dengue cases, as they can lead to further platelet loss. Antibiotics are effective against bacterial infections, while dengue is viral, making antibiotics ineffective for dengue treatment. Dengue patients typically show Immunoglobulin M (IgM) antibodies 3-4 days after the onset of fever, so testing within the first three days might yield a negative result. The NS-1 antigen test can also return negative after 5-6 days of fever. Proper timing of tests is essential for accurate diagnosis. If IgG antibodies are present, it indicates a secondary dengue infection, and the patient should be hospitalised immediately to prevent worsening conditions. A second dengue infection is more severe because the body’s antibodies from the first infection can complicate the immune response,” Dr Gupta commented.

“Since there has been a delayed start to the monsoons and scanty rainfall, only a few cases have been reported. The season of dengue and malaria starts from mid-July. In the last 4 days, 3 malaria cases have been confirmed and we have 1 dengue patient. Whereas in the outdoors, the footfall of the patients has increased to 20 per cent for screening and tests. But since the government is already undertaking sufficient preventive measures, the cases are in control,” said Dr MS Purkait, medical superintendent, Techno India DAMA Hospital.

Speaking to The Statesman, Dr Netai Pramanik, former professor at School of Tropical Medicine, Kolkata, said, “Dengue, also known as break-bone fever, can become more severe with a second infection. The antibodies from the first infection can react with the new antibodies from the second infection, potentially causing serious problems in the kidneys, lungs, intestines, or brain. This reaction can also damage capillaries, leading to the leakage of plasma, red blood cells, and platelets. One symptom of this is purpura, where blood vessels leak blood under the skin, appearing as reddish-purple spots on the feet and legs. While these spots may disappear on their own, it is important to consult a doctor, especially if bleeding starts from the nose or elsewhere in the body. Menstruating women are particularly vulnerable during dengue due to blood discharge and leakage. Platelet levels need to be monitored daily, and if there is no bleeding and the platelet count (usually 200,000 to 300,000) does not drop below 10,000, external platelet transfusions are not typically necessary.”

Talking about precautions and control of dengue, Dr Pramanik said, “Mosquitoes that spread dengue are active during the day. To lower the risk of getting dengue, protect yourself from mosquito bites by wearing clothes that cover as much of your body as possible, using mosquito nets if sleeping during the day, installing window screens, applying mosquito repellents and utilising coils and vaporisers. When an infected female Aedes mosquito lays eggs, the next progeny will also carry the dengue virus. This process is known as transovarial transmission. Prevent mosquito breeding by managing and modifying the environment to eliminate egg-laying habitats, disposing of solid waste properly, removing artificial containers that can hold water, and covering, emptying and cleaning domestic water storage containers weekly. Additionally, apply appropriate insecticides to outdoor water storage containers. If you contract dengue, it’s important to rest, drink plenty of liquids, use paracetamol for pain relief and watch for severe symptoms, contacting your doctor immediately if they occur.  It is a common belief that papaya leaves can increase platelet counts, but this has not been proven by allopathic research. However, consuming papaya leaves is generally considered beneficial unless the patient has allergies.”

Dr Pinaki Dey, consultant physician, ILS Hospitals, Dumdum, said, “It is commonly known that dengue patients need to consume plenty of fluids or liquid foods. However, excessive fluid intake can also be harmful, leading to fluid accumulation in the chest or abdomen. This is because, generally, between five to seven days after the onset of symptoms, fluid may leak from the blood vessels. If excessive fluid is consumed, it can lead to dangerous accumulation in the chest and abdomen.”