How dengue in India is linked to climate change

The lights above washing the hospital corridor with a dim glow, a frantic Jenpu Rongmei rushed to see his 12-year-old nephew Nina who had been admitted the night before with fever and body ache. He was too late.

The young boy had succumbed to dengue, a neglected tropical disease that was entirely alien to the people of Nagaland till very recently.

A month later, Jenpu remembers every detail of that evening -- the dull light in the hospital, the faces around, the intense grief and the sheer disbelief that Nina could have gone so soon and so suddenly.

"When I got the news that my nephew was admitted, I thought he would be fine. I didn't think dengue could be deadly," Jenpu, who runs the NGO CanYouth to help young people in their education, said.

As the mosquito-borne disease increases its spread, Nina's untimely death is the latest in the devastating crisis sweeping across the Northeast and other states in India.

The spread of the disease even in autumn has been attributed to a late withdrawal of the monsoon, a factor of climate change.

The transmission of dengue is closely associated with three key factors -- rainfall, humidity and temperature -- that dictate the geographies in which it spreads and the transmission rate of the viral infection caused by the dengue virus (DENV), and transmitted to humans through the bite of infected mosquitoes.

The Lancet noted in its global annual countdown on the health impacts of climate change that the number of months suitable for dengue transmission by Aedes aegypti mosquitoes has risen to 5.6 months each year in India. It accounts for a 1.69 per cent annual increase between 1951-1960 and 2012-2021.

According to Dr Niesakho Kire, state programme officer of the National Centre for Vector Borne Disease Control (NCVBDC), the first case of dengue in Nagaland was reported only eight years ago in June 2015. The numbers have been steadily rising since with the state reporting 2,900 confirmed infections this year, the highest so far.

With many cases going unreported due to lack of awareness, inadequate testing, and reliance on home remedies, the figures could be just the tip of the proverbial iceberg.

"Climatic change is undoubtedly a significant factor. Rising temperatures, erratic rainfall, and urbanisation provide a fertile ground for Aedes mosquitoes, carriers of the dengue virus, to breed. Dimapur, once a city with moderate temperatures, has now become one of the hotspots. Dengue has seeped into the hilly regions, affecting villages where healthcare facilities are limited,” Kire told PTI.

Unpredictable rains, coupled with rampant construction and inadequate drainage systems, create stagnant water pockets that are ideal breeding grounds for mosquitoes, Kire explained.

The impact of climate change on Nagaland's weather patterns is stark.

According to Jenpu, villagers, once accustomed to wearing jackets in October, now opt for shorts as temperatures and humidity have soared over the years with rainfall patterns becoming erratic.

The situation is similar in neighbouring Manipur where the incidence of dengue has increased manifold in the past few years. Dengue cases were first reported in the state in 2007 and the numbers have been rising since.

From January this year to October 13, Manipur recorded 1,338 dengue cases, 835 more than what was reported in 2022.

The dengue story finds echo in the hill state of Uttarakhand, some 2,500 km from Nagaland, where 28-year-old Arushi woke up one morning with a debilitating fever, body ache and red spots all over her body.

"I have battled colds and even faced COVID-19, but this experience was unlike anything I have encountered. As the days passed, my mother shared the alarming news that numerous people in our neighbourhood had fallen victim to the dengue virus," Arushi, who hadn't heard about the disease while growing up in Dehradun, told PTI.

The official number of dengue cases in Uttarakhand has surged past the 3,000 mark this year, with more than 1,000 cases reported in the capital Dehradun alone and an additional 736 in Pauri district.

Manira Dhasmana, associate consultant, of internal medicine, at Dehradun's Max Super Speciality Hospital, added that more cases lead to complications like dengue haemorrhagic fever and dengue shock syndrome. These are characterised by severe plasma leakage, bleeding, and organ involvement that can be fatal.

“The cases are more in areas prone to waterlogging during rains. Due to high loads of patients suffering from dengue fever, we set up special beds this year...,” Dhasmana told PTI.

Most people with dengue have mild or no symptoms and will get better in one or two weeks. Symptoms include high fever, severe headache, muscle and joint pains, swollen glands and rash.

However, severe dengue symptoms such as shooting abdominal pain, rapid breathing, bleeding gums or nose, and blood in vomit or stool, often come after the fever has gone away, and can be fatal.

According to public health expert Poornima Prabhakaran, changing climatic conditions become more favourable for the spread and disease transmission potential of viruses and their vectors.

“Steadily rising temperatures affect the pattern of transmission of disease agents like viruses as well their vectors through a number of pathways,” Prabhakaran, director, Centre for Health Analytics Research and Trends, Trivedi School of Biosciences, Ashoka University, told PTI.

India currently bears the majority of the global dengue burden, which can be attributed to various factors, including urbanisation, travel, trade, climate change, viral evolution, and the absence of effective vaccines and drug treatments.

According to the data shared by NCVBDC, India recorded nearly 95,000 cases and 91 deaths this year by September 17. The number was 2,33,251 (2.33 lakh) for last year, with 303 deaths. Experts say the actual numbers are very high and the majority of the cases don't even get reported.

“Climate change is influencing the incidence of Aedes aegypti and Aedes albopictus mosquito-borne dengue illnesses,” according to Nitish Mondal, from Sikkim University, Gangtok, who authored a paper published in The Lancet journal in March this year.

“By 2012–13, the face of dengue incidence in India radically transformed. Dengue has become an annual epidemic in many parts of Southeast Asia, and the disease is becoming more hazardous as the environment changes,” Mondal said.

Despite the escalating threat, vaccines and treatments for dengue remain elusive.

“One of the main challenges in developing a vaccine for dengue is that the virus has four different serotypes or variants, making it difficult to create a vaccine that can target all four equally,” explained dengue expert Neelika Malavige.

“With the virus evolving faster during intense transmission, new variants can emerge and lead to massive outbreaks, causing an increase in disease severity,” Malavige, head of the Dengue Global Program and Scientific Affairs (India) at international not-for-profit Drugs for Neglected Diseases initiative (DNDi), told PTI.

A recent study conducted by researchers at the Indian Institute of Science (IISc) in Bengaluru revealed that the dengue virus has undergone “dramatic” evolution over the last few decades in India. This underscores the urgent need to develop a vaccine that targets the strains found in the country.