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Mosquitoes: Why They Bite Us, and How to Escape From Them

WITH ALL THE JOYS OF SUMMER , he has an important drawback – mosquitoes. The only one is able to deprive you of sleep at midnight: in the dark it will squeak thinly (in fact, this sound is emitted by wings), when you turn on the light, hide, and then it still bites, and in the morning you wake up with an itchy blister on your skin. But besides these inconveniences, mosquitoes are really dangerous. According to 2017 data, these are the most dangerous animals in the world, more deadly than large predators or poisonous insects, spiders and snakes. We will tell you how mosquitoes choose victims, what infections they carry and what to do with them.                  

Why do they bite us

Blood-sucking mosquitoes are a family of dipterans with the Latin name Culicidae. The earliest mosquitoes are found in Cretaceous Burmese amber, however, they may have existed in the Jurassic period. Mosquitoes live on all continents except Antarctica, and in Russia there are one hundred species.          

Mosquitoes do not feed on blood – they (both males and females) eat nectar and plant juices. But blood is needed for laying eggs, their quantity and even the very possibility of their formation directly depends on its volume . Therefore, the oral apparatus of females is designed so that they can pierce the skin of animals and humans. One clutch contains from 30 to 150 eggs (rarely – up to 280), and the female can lay eggs up to 1 time in 2-3 days. Development from egg to adult mosquito takes in two weeks on average.                         

Most species of mosquitoes use the blood of mammals and birds for reproduction , some species are capable of biting reptiles, amphibians and even fish. And people became not only the main suppliers of blood for these insects, but also helped them spread throughout the planet: first in the bottoms of ships, filled with water, worn out tires or containers with cut flowers, now – in cars, trains and airplanes.              

How they choose a victim

Entomologists report that the chemical trail of carbon dioxide we breathe out helps mosquitoes find their target up to 50 meters away. It turns out that the more often you breathe, the higher the risk of being bitten – which is why mosquitoes often bite children, pregnant women, and people with a large body weight. During physical labor or sports, the respiration rate and the release of carbon dioxide also increase.           

Before a mosquito sees a victim, it detects chemical signals. It is believed that the sense of smell makes the greatest contribution to the search, but in general several sensory systems are used for it at once: smell, vision, perception of temperature and humidity, taste. There are 72 types of olfactory receptors on the antennae of a mosquito, and most of them are needed to find the source of blood. At least 27 types of these receptors are tuned to detect substances that animals and humans secrete with sweat.               

The mosquito determines not only the location of the victim, but also its physical and chemical characteristics. The complex receptor apparatus, reading the molecules spread by our bodies, forms the so-called odoral map in the mosquito’s brain – it contains the information the insect needs about us. The female mosquito “ remembers ” which card was most favorable for laying, and gives preference to a victim with similar characteristics. That is why mosquitoes bite someone more often, and someone less often or almost never.            

At a distance of about a meter from a potential victim, the mosquito begins to distinguish many parameters: skin temperature, metabolic characteristics and human microflora. There are data about that attract mosquitoes lactic acid (the level of which rises even after the physical load), ammonia, acetone. It looks like human blood alcohol is also attractive to insects.            

Microbes living on the skin produce a whole bunch of components – there are more than three hundred of them, and the composition depends on the environment and human genetic characteristics. The composition of the skin microbiota also influences the choice of the mosquito victim, and people with a more diverse composition of skin bacteria will bite less often than with more uniform ones. Hypotheses about the possible effect of blood type or blood sugar levels have not yet been confirmed.                 

Why bites itch and what to do  

Before the female mosquito starts drinking blood, she injects saliva into the skin, which contains pain relievers and anticoagulants that prevent blood from clotting. These foreign proteins cause itching, swelling and redness. A common reaction to a mosquito bite is an immediate blister and redness that peaks after twenty minutes. Then, in for a day and a half, there is a pruritic papule, and in seven to ten days it disappears. In most cases, mosquito bites are not dangerous, although they cause discomfort. But there are exceptions.                

An allergy to mosquito bites, or skeeter syndrome , can manifest itself as severe itching and pain at the site of the bite, a large blister that sometimes grows and turns into a spot. Reactions such as nausea and vomiting, up to fever, anaphylactic shock and loss of consciousness are also possible .          

One way to reduce itching is to warm up the bite site; there are even special gadgets for this. When warmed up, the foreign protein is destroyed faster, and the method can help, but in case of allergies, it is unsafe. If the edema grows, and the state of health worsens, you need to apply cold to the bite site. You can take an antihistamine, apply glucocorticosteroid ointment to the skin. If all these measures do not help or it gets worse, you need to see a doctor.                

How mosquitoes can infect

Mosquitoes, without getting sick themselves, carry bacteria, viruses and parasites from person to person. It is definitely impossible to get HIV through a mosquito bite , but they carry the causative agents of malaria, yellow fever, dengue fever, tularemia, lymphatic filariasis (“elephantiasis”) and encephalitis. More than seven hundred million people fall ill with these infections every year, and deaths are in the millions – malaria alone kills 435 thousand people every year. Mosquitoes spread dangerous infections in Africa, South and Central America, Asia – and in Russia too.                   

It is not surprising that the fight against these insects is becoming an important task for entire countries and regions. For the prevention of certain diseases, there are vaccines, but it is necessary to control and population of mosquitoes – it is important, for example, drain swamps, working with ponds, monitor the conditions in the basement rooms – there are not only live larvae, but and wintering adults. For the mass fight against mosquitoes, certain types of fish and dragonflies are bred . For example, the Sochi nursery ” mosquito fish ” distributes free mosquito fish to fish, which feed on mosquito larvae. Even in water, preparations based on the bacteria Bacillus thuringiensis are used – mosquito larvae eat up bacterial spores and die.                    

Now the “World Mosquito Program” is being implemented to combat viral infections. As part of the program, mosquitoes are infected with the bacteria Wolbachia, which suppresses the reproduction of viruses. The bacterium quickly spreads among mosquitoes, infects up to 90% of the population within 10–20 weeks and remains in it for at least five years. The method is already being used in Australia, Vietnam, Indonesia, Colombia, Brazil and China.                 

Another option is the genetic modification of mosquitoes, as a result of which they produce non-viable offspring. If a certain number of genetically modified males are released annually , the overall mosquito population will decline. The method has been tested on the Cayman Islands, the party modified male Aedes aegypti mosquitoes has reduced the number to 62%. Later, successful tests were carried out in Panama, Malaysia and Brazil , and work began in Africa. Other genetic modifications are under development: for example, preventing viruses in the mosquito’s body from multiplying or causing the death of insect cells when a virus enters.              

How to protect yourself

First, you can use means that physically restrict access to the body – these are mosquito nets, mosquito nets, bed curtains and thick clothing. Secondly, insecticides, that is, substances that destroy insects, and repellents that repel them , fight mosquitoes . Insecticides are toxic, and they are not applied to the skin , but they can be used to treat rooms. To distribute the substance over a large area, for example, in a room, fumigators are used – ignited spirals or electrical devices with replaceable cartridges. It is important that the windows are open in the room – then insecticides will not accumulate to quantities hazardous to humans.                  

Repellents can be applied to and applied near the skin . They act in different ways: for example, they bind to the olfactory receptors of the mosquito and block their work, or turn the smell of the victim attractive to the insect into repulsive. The most effective repellent according to research is the synthetic compound DEET (N, N-diethyl-3-methylbenzamide). It is safe when applied to the skin and lasts up to five hours; it is advisable to wash it off before going to bed, wash your hands after each use and avoid contact with mucous membranes. A good alternative is products with 2 % soybean oil, which are effective within 94 minutes on average .                         

What tools don’t work 

According to the advertisements, the best protection for children is wristbands impregnated with repellents. But in fact, they are useless and mosquitoes bite the skin just four centimeters from the bracelet. In natural repellents with citronella effect is very short (less than 20 minutes). Although candles with this substance have been used since 1882, in the study they were indistinguishable from placebo candles, which release heat, carbon dioxide and moisture, and distract mosquitoes slightly . Ultrasonic devices, supposedly repelling mosquitoes, have also been shown to be completely ineffective.                       

They try to use essential oils against mosquitoes – in aroma lamps or directly on the skin . You can find mentions that mosquitoes do not like camphor, geranium, eucalyptus, tea tree, citrus fruits, tomato tops, walnut leaves, basil, bird cherry, elderberry, wheatgrass, vanilla, anise, cloves, calendula, valerian, eucalyptus, lavender, thyme, geranium, mint, cedar nut oil, tar. But none of these components have been effective in human studies . Geranium essential oil had little activity , but the indicators are not even close to being comparable to DEET.

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