A Summertime Sting
A Summertime Sting
Joanna Cheng
Edited by Teknos Staff 2019-2020
It’s that time of year again. Summer brings feelings of freedom, buoyancy, warmth… and itchiness, all thanks to a tiny insect—the mosquito. Not only are these insects the source of endless scratching and fury, they also cause over 3,500,000 cases of disease and 500,000 deaths a year due to the diseases they transmit, such as zika, dengue fever, malaria, chikungunya, and yellow fever [2, 4]. Although the world would rejoice if mosquitoes were wiped off the face of the Earth, they do have some benefits, despite being one of the deadliest creatures in existence.
A mosquito’s method for seeking out its victim is highly sophisticated, involving three different cues: olfactory (the sense of smell), visual, and thermal. From 10-15 meters away, mosquitoes are able to smell and fly towards the plumes of carbon dioxide we exhale. This odorant activates the mosquito’s visual sense, and it begins to look for the human nearby. Once it approaches the human, the mosquito detects other skin odorants along with the thermal signature we give off, allowing it to find a suitable place to land, such as an arm or a leg [9].
After a successful landing, mosquitoes use their proboscis to probe for a blood vessel while depositing saliva into the host [7]. Their saliva contains a vast array of microbes and proteins that act as anticoagulants, preventing blood from clotting so that the mosquito can feed. However, most humans are allergic to some components of mosquito saliva, causing the telltale itchiness and the activation of the inflammatory response in the target [8]. This response begins with the arrival of mast cells, which release molecules called histamines. Histamines cause blood vessels near the area of the bite to dilate, allowing leukocytes and other immune system fighters to arrive at the site. The dilation of blood vessels is the reason that mosquito bites become red, swollen, and hot [7]. This well-coordinated attack of histamines and immune system cells would be useful… if mosquito saliva was dangerous. However, the symptoms of mosquito bites are simply the body’s overreaction to an outside invasion [8].
One common myth about mosquitoes is that all of them bite, while in reality, only female mosquitoes ready to lay eggs consume blood for its rich protein reserves. The proteins they consume allow females to mature the eggs and perform other functions needed to prepare for egg-laying. After a mosquito has ingested a full meal that nearly doubles its weight, it seeks a place to lay about 100-150 eggs. This cycle of blood-feeding and egg-laying is called the gonotrophic cycle, which occurs multiple times throughout the life of a female mosquito [2].
In areas where mosquitoes abound, one can expect an abundance of deadly diseases as well. When a mosquito bites a person, that person’s blood, as well as their pathogens, are ingested by the mosquito and then transmitted when the mosquito bites its next target [4]. To add to the danger, some species that can carry disease have a strong preference for human hosts. The recent trend of global warming has raised concerns over a potential increase in mosquito populations, as these insects thrive in warmer temperatures. Therefore, it is imperative that we find effective methods of controlling these pests [2].
There are several different types of repellents that protect against mosquitoes. Contact irritants make human skin an undesirable place for mosquitoes to land, deterrents suppress blood feeding, and odor maskers prevent mosquitoes from latching on to human odorant traces [6]. However, many populations of mosquitoes are slowly beginning to develop resistance to these repellents [2]. As a countermeasure, scientists have developed transmission-blocking vaccines (TBVs). The antibodies produced by this vaccine are ingested by the mosquitoes when they bite and prevent the development of the malaria parasite in the mosquito’s gut. Another unique method of mosquito control uses a type of bacteria called Wolbachia. Scientists discovered that when this bacteria was introduced to mosquitoes carrying viruses like dengue and zika, the bacteria outcompeted the viruses, reducing transmission rates [5].
An even more invasive method of controlling mosquitoes has brought up controversy among the scientist community. Research has found that using CRISPR-Cas9, a gene-editing technology, to tamper with the mosquito genome may prevent them from transmitting diseases. Very recently, the Environmental Protection Agency (EPA) approved a plan to release genetically modified mosquitoes in Florida and Texas. The genomes of these insects were changed to code for a protein that would lessen the survival of female offspring and pass down the same genetic modification to male offspring. The EPA claimed that there would be no harm to humans since only male mosquitoes were being released and tested. However, many were concerned by the hastiness in the approval of this plan [3]. Even though there may be no harm to humans, no one can tell what effect these genetically modified mosquitoes will have on the predators of these insects. In the meantime, scientists should focus on developing less invasive methods of mosquito control whose ethics many scientists agree with.
Although it may seem like mosquitoes do not benefit mankind in any way, there is still some good that comes out of having them on this Earth. First of all, they are essential to several ecosystems’ food webs by acting as food for fish, birds, and other predators. This is true for virtually all organisms, since ecosystems are so tightly connected that disrupting one small section will throw the entire system off balance. Furthermore, mosquitoes help by pollinating plants; since male mosquitoes don’t bite, they must obtain their nutrition from nectar. Finally, only about a hundred species of mosquitoes actually feed on humans, while the rest of the over 3,000 total species feed on other animals [1].
As the summer grows hotter, more and more mosquitoes are coming out of hiding, once again reminding us of the pain and the dangers associated with these tiny insects. These pests, in addition to the quarantine, give us two good reasons to stay inside, safe and sound. However, if you do decide to go outside and risk those nasty bites, make sure to cover up and stay safe. (Yes, this was written by a human that mosquitoes have found quite tasty this summer.)
References
[1] Besansky, N. (2016, February 19). Mosquitoes: What are they good for? (Interview by A. Shapiro) [Transcript]. NPR. Retrieved June 16, 2020, from https://www.npr.org/ 2016/02/19/467395225/mosquitoes-what-are-they-good-for
[2] Duvall, L. B. (2019). Mosquito host-seeking regulation: Targets for behavioral control. Trends in Parasitology, 35(9), 704-714. https://doi.org/10.1016/j.pt.2019.06.010
[3] Frazin, R. (2020, June 15). EPA faces suit over plan to release genetically engineered mosquitoes. The Hill. Retrieved June 16, 2020, from https://thehill.com/ policy/energy-environment/502827-epa-faces-suit-over-plan-for-releasing-genetically-engineered
[4] Gao, H., Cui, C., Wang, L., Jacobs-Lorena, M., & Wang, S. (2020). Mosquito microbiota and implications for disease control. Trends in Parasitology, 36(2), 98-111. https://doi.org/10.1016/j.pt.2019.12.001
[5] How it works. (n.d.). World Mosquito Program. Retrieved June 16, 2020, from https://www.worldmosquitoprogram.org/en/work/wolbachia-method/how-it-works
[6] Islam, J., Zaman, K., Duarah, S., Raju, P. S., & Chattopadhyay, P. (2017). Mosquito repellents: An insight into the chronological perspectives and novel discoveries. Acta Tropica, 167, 216-230. https://doi.org/10.1016/j.actatropica.2016.12.031
[7] Pingen, M., Schmid, M. A., Harris, E., & McKimmie, C. S. (2017). Mosquito biting modulates skin response to virus infection. Trends in Parasitology, 33(8), 645-657. https://doi.org/10.1016/j.pt.2017.04.003
[8] Stempien, A. (2015, August 19). Why do mosquito bites itch? The science of summer. Smithsonian. Retrieved June 16, 2020, from https://ssec.si.edu/stemvisions-blog/why-do- mosquito-bites-itch-science-summer
[9] van Breugel, F., Riffell, J., Fairhall, A., & Dickinson, M. H. (2015). Mosquitoes use vision to associate odor plumes with thermal targets. Current Biology, 25(16), 2123-2129. https://doi.org/10.1016/j.cub.2015.06.046
