The Mosquito and Her Diseases
It has been one of the most universally recognizable and aggravating sounds on earth for 190 million years—the humming buzz of a mosquito. After a long day of hiking while camping with your family or friends, you quickly shower, settle into your lawn chair, crack an ice-cold beer, and exhale a deep, contented sigh. Before you can enjoy your first satisfying swig, however, you hear that all-too-familiar sound signaling the ambitious approach of your soon-to-be tormentors.
It is nearing dusk, her favorite time to feed. Although you heard her droning arrival, she gently lands on your ankle without detection, as she usually bites close to the ground. It’s always a female, by the way. She conducts a tender, probing, ten-second reconnaissance, looking for a prime blood vessel. With her backside in the air, she steadies her cross-hairs and zeros in with six sophisticated needles. She inserts two serrated mandible cutting blades (much like an electric carving knife with two blades shifting back and forth), and saws into your skin, while two other retractors open a passage for the proboscis, a hypodermic syringe that emerges from its protective sheath. With this straw she starts to suck 3–5 milligrams of your blood, immediately excreting its water, while condensing its 20% protein content. All the while, a sixth needle is pumping in saliva that contains an anticoagulant preventing your blood from clotting at the puncture site. This shortens her feeding time, lessening the likelihood that you feel her penetration and splat her across your ankle. The anticoagulant causes an allergic reaction, leaving an itchy bump as her parting gift. The mosquito bite is an intricate and innovative feeding ritual required for reproduction. She needs your blood to grow and mature her eggs.
Please don’t feel singled out, special, or view yourself as a chosen one. She bites everyone. This is just the inherent nature of the beast. There is absolutely no truth to the persistent myths that mosquitoes fancy females over males, that they prefer blondes and redheads over those with darker hair, or that the darker or more leathery your skin, the safer you are from her bite. It is true, however, that she does play favorites and feasts on some more than others.
Blood type O seems to be the vintage of choice over types A and B or their blend. People with blood type O get bitten twice as often as those with type A, with type B falling somewhere in between. Disney/ Pixar must have done their homework when portraying a tipsy mosquito ordering a “Bloody Mary, O-Positive” in the 1998 movie A Bug’s Life
. Those who have higher natural levels of certain chemicals in their skin, particularly lactic acid, also seem to be more attractive. From these elements she can analyze which blood type you are. These are the same chemicals that determine an individual’s level of skin bacteria and unique body odor. While you may offend others and perhaps yourself, in this case being pungently rancid is a good thing, for it increases bacterial levels on the skin, which makes you less alluring to mosquitoes. Cleanliness is not next to godliness, except for stinky feet, which emit a bacterium (the same one that ripens and rinds certain cheeses) that is a mosquito aphrodisiac. Mosquitoes are also enticed by deodorants, perfumes, soap, and other applied fragrances.
While this may seem unfair to many of you, and the reason remains a mystery, she also has an affinity for beer drinkers. Wearing bright colors is also not a wise choice, since she hunts by both sight and smell— the latter depending chiefly on the amount of carbon dioxide exhaled by the potential target. So all your thrashing and huffing and puffing only magnetizes mosquitoes and puts you at greater risk. She can smell carbon dioxide from over 200 feet away. When you exercise, for example, you emit more carbon dioxide through both frequency of breath and output. You also sweat, releasing those appetizing chemicals, primarily lactic acid, that invite the mosquito’s attention. Lastly, your body temperature rises, which is an easily identifiable heat signature for your soon-to-be tormentor. On average, pregnant women suffer twice as many bites, as they respire 20% more carbon dioxide, and have a marginally elevated body temperature. As we will see, this is bad news for the mother and the fetus when it comes to infection from Zika and malaria.
Please don’t go on a shower, deodorant, and exercise strike or shelve your beloved beer and bright T-shirts just yet. Unfortunately, 85% of what makes you attractive to mosquitoes is prewired in your genetic circuit board, whether that be blood type; natural chemical, bacteria, or CO2 levels; metabolism; or stink and stench. At the end of the day, she will find blood from any exposed target of opportunity.
Unlike their female counterparts, male mosquitoes do not bite. Their world revolves around two things: nectar and sex. Like other flying insects, when ready to mate, male mosquitoes assemble over a prominent feature, ranging from chimneys to antennas to trees to people. Many of us grumble and flail in frustration as that dogged cloud of bugs droning over our heads shadows us when we walk and refuses to disperse. You are not paranoid, nor are you imagining this phenomenon. Take it as a compliment. Male mosquitoes have graced you with the honor of being a “swarm marker.” Mosquito swarms have been photographed extending 1,000 feet into the air, resembling a tornado funnel cloud. With the cocksure males stubbornly assembled over your head, females will fly into their horde to find a suitable mate. While males will mate frequently in a lifetime, one dose of sperm is all the female needs to produce numerous batches of offspring. She stores the sperm and dispenses them piecemeal for each separate birthing of eggs. Her short moment of passion has provided one of the two necessary components for procreation. The only ingredient missing is your blood.
Returning to our camping scenario, you just finished your strenuous hike and proceed to the shower, where you richly lather up with soap and shampoo. After toweling off, you apply a healthy dose of body spray and deodorant before finally putting on your bright red-and-blue beachwear. It is nearing dusk, dinnertime for the Anopheles mosquito, and you sit down in your lawn chair to relax with that well-deserved cold beer. You have done everything in your power to lure a famished female Anopheles mosquito (and by the way, I just moved to the seat that is farthest from you). Having just mated in a swarming frenzy of eager male suitors, she willingly takes your bait and makes off with a few drops of your blood.
She has taken a blood meal three times her own body weight, so she quickly finds the nearest vertical surface and, with the aid of gravity, continues to evacuate the water from your blood. Using this concentrated blood, she will develop her eggs over the next few days. She then deposits roughly 200 floating eggs on the surface of a small pool of water that has collected on a crushed beer can that was overlooked during cleanup as you and your party headed home. She always lays her eggs in water, although she does not need much. From a pond or stream to a minuscule collection in the bottom of an old container, used tire, or backyard toy, any will suffice. Certain types of mosquitoes desire specific types of water—fresh, salt, or brackish (a mixture)—while for others, any water will do the trick.
Our mosquito will continue to bite and lay eggs during her short life span of an average one to three weeks to an infrequent maximum longevity of five months. While she can fly up to two miles, she, like most mosquitoes, rarely ranges farther than 400 meters from her birthplace. Although it takes a few days longer in cool weather, given the high temperatures, her eggs hatch into wiggling water-bound worms (children) within two to three days. Skimming the water for food, these quickly turn into upside-down, comma-shaped tumbling caterpillars (teenagers) who breathe through two “trumpets” protruding from their water-exposed buttocks. A few days later, a protective encasement splits and healthy adult mosquitoes take to flight, with a new generation of succubus females anxious to feed on you once more. This impressive maturation to adulthood takes roughly one week.
The repetition of this life cycle has been uninterrupted on planet Earth since the first appearance of modern mosquitoes. Research suggests that mosquitoes, identical in appearance to those of today, surfaced as early as 190 million years ago. Amber, which is essentially petrified tree sap or resin, represents the crown jewels of fossilized insects, for it captures minute details such as webs, eggs, and the complete intact innards of its entombed. The two oldest fossilized mosquitoes on record are those preserved in amber from Canada and Myanmar dating from 105 to 80 million years ago. While the global environments these original bloodsuckers patrolled would be unrecognizable to us today, the mosquito remains the same.
Our planet was vastly different from the one we currently inhabit, as were most of the animals that called it home. If we navigate the evolution of life on earth, the devious partnership between insects and disease becomes strikingly clear. Single-cell bacteria were the first life-form to appear not long after the creation of our planet roughly 4.5 billion years ago. Spawning from a cauldron of gases and primordial oceanic ooze, they quickly established themselves, forming a biomass twenty-five times larger than all other plants and animals combined, and the foundation of petroleum and other fossil fuels. In one day, a single bacterium can spawn a culture of over four sextillion (twenty-one zeros), more than all other life on the planet. They are the essential ingredient and building block for all other life on earth. As specification commenced, asexual, cell-dividing bacteria adapted and found safer and more favorable homes as permanent guests on or in other host creatures. The human body contains one hundred times as many bacterial cells as it does human cells. For the most part, these symbiotic relationships are generally beneficial to the host as well as to the bacterial boarders.
It is the handful of negative pairings that cause problems. Currently, over one million microbes have been identified, yet only 1,400 have the potential to cause harm to humans. Twelve ounces (a standard-size pop can) of the toxin produced by the bacterium that causes botulism food poisoning, for example, is enough to kill every human being on the planet. Viruses then arrived, quickly followed by parasites, both mirroring the housing arrangements of their bacterial parent, ushering in the potent combinations for disease and death. The sole parental responsibility of these microbes is to reproduce . . . and . . . to reproduce. Bacteria, viruses, and parasites, along with worms and fungi, have triggered untold misery and have commanded the course of human history. Why have these pathogens evolved to exterminate their hosts?
If we can set aside our bias for a moment, we can see that these microbes have journeyed through the natural selection voyage just as we have. This is why they still make us sick and are so difficult to eradicate. You may be puzzled: It seems self-defeating and detrimental to kill your host. The disease kills us, yes, but the symptoms of the disease are ways in which the microbe conscripts us to help it spread and reproduce. It is dazzlingly clever, when you stop to think about it. Generally, germs guarantee their contagion and replication prior
to killing their hosts.
Copyright © 2019 by Timothy C. Winegard. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.