New research at the Rajiv Gandhi Centre for Biotechnology and published in The Federation of American Societies of Experimental Biology has found out that dengue becomes more severe in animal models when its virus is exposed to higher temperature. It is because viruses can replicate faster when exposed to warmer temperatures and can be spread to humans more quickly. The researchers of the study also observed that global warming could be possibly changing the disease dynamics. While dengue symptoms continue to be mild in most people, in many others it can be fatal.

“With the onset of monsoon, viral infections are on a constant rise among different age groups. Among these, dengue is the most common viral infection that is caused due to mosquito bites. In recent times, there has been a growing concern over the severity of the dengue virus and its implications for public health. Therefore, it is important to understand the various factors for timely intervention,” says Dr. Vinay Bhat, Consultant – Internal Medicine, Manipal Hospital, Ghaziabad.

“The severity of dengue virus infections is influenced by multiple factors, with global warming playing a significant role in creating conducive conditions for mosquito breeding, viral replication, and altered transmission dynamics. Efforts to mitigate the impact of dengue and other vector-borne diseases should include addressing the climate change-related factors that contribute to their spread,” says Dr. Ather Pasha – Consultant, General Medicine, CARE Hospitals, Banjara Hills, Hyderabad.

There are several factors that contribute to the increasing severity of dengue, with global warming playing a significant role. Some of the major ones include:

Reasons why dengue severity is on rise

Viral strains

Different strains of the dengue virus exist, with some being more virulent than others. Co-circulation of multiple strains can lead to more severe cases due to the phenomenon known as antibody-dependent enhancement (ADE), where exposure to one strain increases the risk of severe disease upon subsequent infection with another strain.

Weak immune responses

In some cases, a history of dengue infection can weaken the immune system’s response, making individuals more susceptible to severe forms of the virus upon subsequent infections.

Delayed diagnosis and treatment

Late diagnosis and inadequate medical care can contribute to the progression of dengue to its severe forms, such as dengue haemorrhagic fever (DHF) or dengue shock syndrome (DSS).

Water stagnation

This is one of the major contributing factors of dengue. It provides a conducive environment for the breeding of the primary vector mosquitoes, Aedes aegypti and Aedes albopictus. These mosquitoes thrive in urban and semi-urban environments and are responsible for transmitting the dengue virus to humans.

“The severity of dengue virus infections can be influenced by a variety of factors, and global warming is indeed playing a role in exacerbating some of these factors,” says Dr Pasha.

Dr Pasha shares reasons why dengue virus is turning severe and how global warming is contributing:

Vector proliferation

Dengue is primarily transmitted by Aedes mosquitoes, especially Aedes aegypti. Warmer temperatures and increased humidity due to global warming create more favourable conditions for these mosquitoes to breed and thrive, leading to a higher population of vectors capable of spreading the virus.

Increased transmission window

Warmer climates extend the lifespan and activity period of mosquitoes, allowing them to transmit the virus for a longer duration throughout the year. This prolonged transmission window can result in a higher number of cases.

Altered mosquito behaviour

Global warming can affect the behaviour of Aedes mosquitoes, making them more aggressive in seeking blood meals, which can lead to an increase in human-mosquito contact and subsequent transmission of the virus.

Expanded geographic range

Warmer temperatures allow Aedes mosquitoes to thrive in areas that were previously too cold for them. This expansion of their range exposes new populations to the virus, potentially leading to more severe outbreaks.

Limited resources

Many regions facing dengue outbreaks are also vulnerable to the impacts of climate change. Limited resources to address both health infrastructure and climate-related challenges can exacerbate the severity of outbreaks.

Role of global warming

Global warming, driven by climate change, plays a pivotal role in exacerbating the severity of dengue fever.

Dr Bhat shares some of the reasons:

Extended mosquito breeding seasons: Warmer temperatures extend the breeding seasons of Aedes mosquitoes, increasing their population density and the rate of dengue virus transmission.

Faster virus replication: Elevated temperatures enhance the replication of the dengue virus within mosquitoes, leading to higher viral loads and a greater potential for transmission to humans.

Expanded geographical range: Rising temperatures allow Aedes mosquitoes to thrive in regions that were previously unsuitable for their survival, exposing new populations to dengue transmission.

Altered mosquito behaviour: Warmer temperatures can affect the behaviour of Aedes mosquitoes, making them more aggressive and likely to bite multiple times, increasing the risk of virus transmission.

Heavy rainfall: Climate change can lead to increased rainfall and more frequent extreme weather events, creating stagnant water bodies that serve as breeding sites for mosquitoes.

“The intertwining of these factors creates a complex scenario where the severity of the dengue virus is amplified. Addressing this challenge requires a multi-faceted approach that involves vector control, public health education, improved diagnosis and treatment, and addressing the broader issue of climate change. Additionally, it is also recommended to maintain proper hygiene especially during monsoon. One must avoid stagnation of water in the neighbourhood, use mosquito nets and repellents, wear protective clothing and install screens on doors and windows to keep mosquitoes out of living spaces. If a dengue vaccine is available, consider getting vaccinated to reduce the risk of infection. Lastly, one must seek medical attention in case of any symptoms like high fever, severe headache, joint pain, and rash,” says Dr Bhat.