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Climate Change and Human Disease Vectors

Climate change has already led to the alteration in geographical distribution of various human disease vectors(2,3). Both migration to cooler climates and higher elevations has been observed(2). It has been suggested that these migration events could in some cases lead to greater disease transmission(1,2). However, extinction events may also be expected which could possibly decrease the number of vectors in a given area(2).

Changes in temperature, humidity, and precipitation, can change the host’s and pathogen’s developmental cycle, population densities, and transmission rates (5). Temperature alone can have an effect on vector biting rates, reproductive cycles, and survival rates (1). It has been suggested that an increase in global temperature may lessen the potential for seasonally lower temperatures which cyclically decrease vector populations(3). Humidity and rainfall also have an effect on vector population dynamics (1,3). Temperature is also known to affect the survival of the pathogens carried by vectors (1).

There is significant variability in how various vector borne diseases are impacted by climate change(1). Climate change has had a mixed effect on Malaria in Africa(1). Drought in some areas has led to decreased malaria transmission risk, whilst other areas have become more suitable to transmission through increased rainfall(1,2). Many confounding variables also make the association between climate change and malaria transmission in Africa difficult to assess(1). Improved infrastructure and socioeconomic factors, along with basic healthcare and preventive care, can decrease the risk of transmission and mortality(1,5). However, the lack of effective healthcare interventions and other protective factors make Dengue fever more prone to the effects of climate change than malaria (1). Similarly to malaria, an increase in precipitation and temperature has led to a higher population density of the mosquitos responsible for Dengue fever and an increase in transmission rates (5). But, in contrast with malaria, urbanization appears to be positively associated with transmission of the virus(1). It has therefore been suggested that efforts to control the spread of Dengue in the wake of climate change may be less effective than those directed towards malaria(1).

Changes in human and animal migration patterns due to climate change have caused an increased in prevalence of vector borne diseases(1,2). Drought and higher temperatures led to human migration to water sources, where fly vectors for Leishmaniasis preside(2). Thus, behavioral alterations due to climate change can cause an increase in prevalence of vector borne diseases. Climate change can also affect migration patterns of vectors, such as those that carry hemorrhagic fever viruses(2). The increase in temperatures at higher altitudes have allowed invasion of new species in the area, which can carry vector borne diseases(3). These species increase their population density at higher altitudes and decrease diversity in the area, causing a higher incidence of vector borne diseases in places not prone to these diseases (2).