Rising temperatures may be directly linked to the increased numbers of dengue fever outbreaks India is currently experiencing.
New evidence suggests that, as temperatures rise, the incubation time of the dengue virus within their mosquito hosts shortens. This leads to increased rates of transmission.
Previous studies have shown a gradual rise in temperature in India. Over the period of 1960 to 2009 average temperatures have risen by just over 0.5°C. This is accompanied by an increased prevalence of heatwaves. These factors combined have lead to a 146 percent increase in probability of heat related mortality.
These factors are leading to a higher prevalence of mosquito populations, as well as breeding populations arising in areas that they would not historically have occurred in.
Mosquito populations are a single factor among several that contribute to rates of dengue fever. There is a complex interaction between the host, vector and the virus, each of which is influenced by the climate.
Critical to the prevalence of the disease is the extrinsic incubation period (EIP). This is the period of time in which the virus is incubating within the mosquito vector before it is capable of being transferred to a new human host.
Studies are showing that hotter temperatures lead to a shorter EIP. A shorter EIP allows for mosquitoes to infect more people in a shorter amount of time, leading to far higher rates of transmission, and therefore outbreaks of the disease become far more common.
It has been shown that the EIP decreases as the temperature rises from 26°C to 30°C. This range of temperatures are common during the hot months and monsoon season within India. This time period presents ideal breeding conditions for the mosquitoes as well as the virus itself.
The research was performed by Srinivasa Rao Mutheneni, scientist at the Council of Scientific and Industrial Research (CSIR)-Indian Institute of Chemical Technology. Analysed within the study were five dengue-endemic states in Western India – Punjab, Haryana, Rajasthan, Gujarat, and Kerala.
The study by Mutheneni is not the only recent report to signal a link between dengue fever and climate change. A recent study in The Lancet claimed dengue fever to be the world’s most rapidly expanding infectious disease, causing between 50 to 100 million infections annually.
The rise in its prevalence is directly linked to climate change. As temperatures rise globally, more and more habitats become suitable for the mosquito vectors of dengue fever to breed. The breeding capacity of the dengue vector species Aedes aegypti has increased 3% since 1990. This rise has been even greater for Aedes albopictus, whose breeding capacity increased by 6% during the same period.
Not only do prevention methods need to be enforced more thoroughly to avoid increased numbers of outbreaks. Plans must be drawn up based on available data of breeding populations to allow for prevention methods to take place in areas which have not historically seen outbreaks occurring.