Welcome curious readers! Today I would like to talk about the relationship between climate change and vector-borne diseases. Yes! There is a positive correlation. Currently, Africa and Asia are known for facing some of the deadliest diseases on the planet, but they are spreading worldwide. Majority of these diseases are vector-borne.
The importance of addressing vector-borne diseases is because malaria and dengue are responsible for high rates of mortality especially in Africa and Asia. Vector-borne diseases have also had a strong influence on the survival rates of children and adults in the past and at present Around 12% of mortality in tropical regions can be directly attributed to vector-borne diseases. The mosquito species that are responsible for dengue and malaria are climate sensitive, which means they have a specific temperature window for optimum establishment (Githeko, et al., 2000). Future climate projections from the IPCC (Intergovernmental Panel on Climate Change) reports predicting a global increase of atmospheric temperature of 0.2°C within the next two decades (IPCC, 2007). The increase in temperature would also increase precipitation and extreme weather events; this will promote the prevalence of vector-borne diseases.
Change in the global climate has the potential to distribute the vectors to other regions of the world, where they have been previously eradicated from or places that have no previous record of the diseases (Patz, et al., 2005). In 2004, The World Health Organisation (WHO) reported that climate change was responsible for 3% of malaria deaths and 3.8% of dengue fever deaths worldwide (Gamage, et al., 2016). There are other factors apart from climate change that affect the distribution of these diseases and they include socio-economic situations and the spatial relationship with the vector breeding sites. Therefore it is important to understand and address the relationship between vector-borne diseases and the future scenarios of climate change.
The mosquito responsible for malaria is known as the Anopheles mosquito (Caminade, et al., 2016). There is a specific climate window for the successful survival of the mosquito; the temperature should be more than 18°C and less than 37°C, alternatively, there can be exceptions to this temperature window as sometimes the vectors develop resistance (Caminade, et al., 2016). In terms of favourable climate for the mosquito, high precipitation is a key condition as it provides breeding sites for the mosquito; while the temperature is responsible for the aggressiveness and mortality of the mosquito (Caminade, et al., 2016). Malaria was responsible for 438,000 deaths worldwide in 2015 according to the World Health Organisation (WHO, 2015).
Dengue fever is still a major vector-borne disease in Asia but is also a global issue as around 100 countries report the spread of the disease. According to a recent estimate, there are around 390 million records of dengue infections annually (Benelli, Mehlhorn, 2016). Moreover, the actual numbers of dengue infection cases have been underreported and misclassified according to the World Health Organisation. There are two types of dengue fever; one is the 'dengue-fever' which has characteristics such as the influenza disease and the other being the fatal version known as the 'dengue haemorrhage' (Guha-Sapir, Schimmer, 2005). The two mosquito species accountable for transmitting dengue infection are the Aedes aegypti and Aedes albopictus.
There is strong evidence that dengue infection is spreading across the Americas during the last decade, even though dengue is generally associated with tropical regions (Butterworth, et al., 2017). The estimated dengue transmission was highest during the summer months but certain places such as Texas showed transmission in the fall and spring seasons as well. It is endemic to the southeastern United States but climate change can potentially lead to an epidemic which would support the transmission of dengue to other states that do not currently support it.
In conclusion, Dengue and malaria are two of the most life-threatening vector-borne diseases in the world where 12% of mortality is associated with the tropics; if strategies aren't in place to control these diseases and eradicate them soon, the probability of these diseases to be a global health challenge is definitive. According to the life cycle of the vector, in this case, the mosquito; increase rainfall, temperature, relative humidity, and extreme weather events can increase the survival rate of the vector. Survival of the vector depends on the geographical locations as well. There are a variety of factors that should be considered when addressing vector-borne disease prevalence such as forest clearing for agricultural purposes; if dengue and malaria were to be controlled on a global scale to have minimum impact on human survival all the factors that contribute to the prevalence should be managed.
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