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Mosquito Distribution and Not-So-Tropical Diseases

By Juliette Blais-Savoie


Tropical forests are well known to be hot spots for infectious diseases. This is due to the high prevalence of disease vectors, animals or insects that can transmit these diseases between humans, most notable of which are mosquitos. Tropical mosquitos are responsible for spreading a host of illnesses including malaria, arbovirus dengue, yellow fever, chikungunya, and zika (Kraemer et al 2019). When a mosquito feeds on a human infected with one of these diseases, the pathogen enters the mosquito and infects any subsequent humans the mosquito feeds on, spreading the disease (Meibalan and Marti 2017). Not all mosquitos are capable of contraction and spread of these pathogens, and mosquito species that are native to non-tropical regions are not compatible with tropical diseases, keeping their regions safe from harm. However, this may soon change due to climate change and human activities (Kraemer et al 2019).


Ae. aegypti from Africa and Ae. albopictu from Asia are two mosquito species that are known tropical disease vectors, and they’re steadily migrating north (Kraemer et al 2019). Climate change has caused global temperatures to rise which is providing suitable habitats for these species farther from the equator (Kraemer et al 2019). While these species don’t have the flight capabilities to spread on their own, our current human trade patterns are providing ample transportation for them to colonize in any habitable territory. Humans have already assisted both species in colonizing the neotropics. Mosquito larvae can hide in potted plants and other items that are shipped internationally. Further enabling their spread, these larvae have the ability to undergo dormancy if an environment is unsuitable (such as northern winters) and then hatch when temperatures rise to their preferred levels. Such traits have allowed Ae. aegypti and Ae. albopictu to spread into North America and Europe, where they can spread compatible diseases (Kraemer et al 2019).


Human urbanization may also be playing a role in mosquitos expanding their habitats. Certain Ae. aegypti subgroups have become highly associated with humans and evolved to reproduce in more urban environments rather than their native habitat of tropical rainforests (Powell and Tabachnick 2013). While there are no tropical rainforests in regions such as the United States and Italy, there is no shortage of urban cities, providing the perfect opportunity for Ae. aegypti infestation, which is estimated to put 49.13% of the global population at risk of contracting arbovirus by 2050 (Kraemer et al 2019). Ae. albopictu is already common in more northern territories and is expected to invade 20 new countries by 2050 (Kraemer et al 2019).


To prevent future disease outbreaks, researchers are working on modelling the spread of Ae. aegypti and Ae. albopictu to predict where they may spread, as well as controlling human-mitigated spread of mosquito larvae and reducing the impacts of climate change to avoid providing these species with even more suitable habitat to infiltrate (Kraemer et al 2019).



Figure 1 (Kraemer et al 2019): a) distribution of Ae. aegypti and Ae. albopictus. b) predicted distribution of Ae. aegypti in 2050. c) distribution of Ae. aegypti and Ae. albopictus. d) predicted habitat suitability of Ae. aegypti and Ae. albopictus. e) Global population expected to live within distribution of Ae. aegypti (RCP 4.5 = low climate change estimate, RCP 6.0 = medium climate change estimate, RCP 8.5 = severe climate change estimate). f) Global population expected to live within distribution of Ae. albopictus.


References


Kraemer, M.U.G., Reiner, R.C., Brady, O.J. et al. Past and future spread of the arbovirus vectors Aedes aegypti and Aedes albopictus. Nat Microbiol 4, 854–863 (2019).


Meibalan, E., & Marti, M. Biology of Malaria Transmission. Cold Spring Harbor perspectives in medicine 7(3), (2017).


Powell, J. R. & Tabachnick, W. J. History of domestication and spread of Aedes aegypti—a review. Mem. Inst. Oswaldo Cruz 108 (Suppl. 1), 11–17 (2013).

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