It’s one of the biggest topics in the news at the moment: climate change. The term, used to describe the changes in weather patterns that Earth has undergone over the course of history, is now part of our everyday lives as experts work to reduce the impact of global warming. Each of the last three decades have been successively warmer at the Earth’s surface than any decade since 1850, and there have also been changes in things such as rainfall and humidity - all of which can affect the life-cycle of mosquitoes and, as a result, mosquito-borne diseases.
Tropical mosquito species like those which transmit malaria, dengue and Zika mostly require high temperatures to complete their life cycles. This means that, as the world begins to increase in heat, the areas in which mosquitoes can thrive continue to increase - particularly for tropical mosquitoes, who can develop more rapidly in these conditions. However, on the other side of this, there is of course a temperature which is too high for mosquitoes to thrive in. The world is currently existing in a delicate balance, with populations of mosquitoes moving to new climates and thriving here - either invited to them or driven out of their current ones by heat changes.
Humidity and rainfall changes are also factors to consider. Both of these factors can have different effects dependent on the disease being transmitted. For example, peak malaria transmission is often directly connected to increased precipitation during the rainy season, as the rain forms surface pools of fresh water which the mosquitoes love to create habitats near. However, it has also been observed that sometimes rainfall can actually wash away larvae and eggs - which can be seen to temporarily lower the malaria rates in a given area.
A contrasting example to this is West Nile virus, which can have epidemics in drought. This is because mosquitoes and the birds they feed on are in close proximity at the more scarce water sources, meaning the virus can more easily be transmitted between species. The mosquitoes also face fewer predators as the predator populations are often reduced in times of drought..
These humidity and rainfall-based effects may result in a geographical shift in the affected area, which can be very dangerous as the human population in the newly affected area may not be naturally immune or possess the infrastructure to deal with any disease outbreaks. Overall, this means that a shift in the affected area can result in an increased morbidity and mortality.
Whilst the challenges of climate change are a global problem, it is those living in developing countries that will be disproportionately affected, and may have the least means to overcome them. In addition to the damage caused by severe weather and rising sea levels, the importance of changes in climate on mosquito-borne diseases should not be overlooked.
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