More heat, more diseases – basic research

By Fabio Gomes

Global warming is redistributing mosquito-borne diseases

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The effects of global warming are already being felt: studies suggest that we have seen the global average temperature rise by one degree Celsius since the beginning of the industrial revolution. This increase, which is obviously small for the layman, is already reflected in an alarming frequency of extreme climatic events, such as prolonged periods of drought, which lead to considerable losses in agricultural production. If the current trend continues, we may have added up to four or five degrees Celsius to world temperature by the end of the century, with ramifications that could inspire a number of disaster films. It remains to be seen whether there will be spectators.

One of the little-discussed effects of global warming is the redistribution of diseases transmitted by mosquitoes, especially Anopheles, that cause malaria. and Aedes, more precisely Aedes aegypti and Aedes albopictus, which are responsible for the spread of viruses such as Dengue, Zika and Chikungunya.

You don’t have to be a map expert to see these insects focus on the hottest areas. In addition to historical and socio-economic factors, such densification also has a direct impact on the biology of these organisms: As with other invertebrates, their body temperature varies depending on the ambient temperature, which regulates their physiology and influences characteristics such as longevity. Fertility and immunity. In fact, in a 2019 study, a group of researchers concluded that differences between countries’ wealth (GDP) explain only 5% of the current distribution of dengue cases, while factors such as temperature and rainfall weighed much more heavily , 68% and 13% each.

The high adaptation of insects in these tropical areas has been critical to several human endeavors throughout history. If the low acclimatization of malaria transmitters in the southern United States and the European Mediterranean helped eradicate the disease in those regions, the difficulty in controlling the vector population and the number of cases of malaria and yellow fever were fundamental to the French gave up the construction of the Panama Canal and later transferred the rights to the Americans.

As the temperature rises, regions that are more temperate today will have features conducive to the spread of mosquitoes and will expand their area of ​​occupation. The extent of this spread will depend on factors such as the size of the deforestation areas and the increase in human occupation on the intensity of global warming and its impact on precipitation patterns. In any case, regions that are little affected by malaria or dengue fever today are more exposed to these diseases. Researchers in the United States have predicted that up to 1 billion people in Europe, Asia, and North America will experience Aedes-borne infections if global warming is not controlled.

A wide variety of areas are predicted in Brazil where mosquitoes can find favorable conditions for reproduction all year round, which would increase the number of disease cases and pressure on the health system. This includes studies that predicted the expansion of the distribution of vectors related to the transmission of malaria by Plasmodium falciparum, a parasite responsible for the deadliest form of the disease, in the Amazon. Several other studies focusing on Africa have shown similar results in expanding the population of these animals. However, in some regions of sub-Saharan Africa, temperatures can get so high that mosquitoes shorten their lifespan and do not have enough time to transmit disease. In this scenario, the malaria incidence could even be reduced in some regions.

Hence, there seems to be a consensus in the prognosis for the occurrence (or recurrence) of these diseases in places that are not currently affected and an increase in cases in regions that are now endemic. Collectively, all of the projections suggest that the consequences of the territorial expansion of vector mosquitoes can be very severe, as much of these regions are inhabited by a population with no immune defenses resulting from prior exposure to these evils and no trained health and health surveillance system to monitor, identify and treat these diseases.

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Fabio Gomes is a professor at the Carlos Chagas Filho Biophysics Institute of the UFRJ and a member of the Cellular Ultrastructure Laboratory Hertha Meyer.

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