The Mosquito Read online

  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.

  Some, like the salmonella “food poisoning” bacteria and various worms, wait to be ingested; that is one animal eating another animal. There is a wide range of water-borne/diarrhea transmitters, including giardia, cholera, typhoid, dysentery, and hepatitis. Others, including the common cold, the twenty-four-hour flu, and true influenza, are passed on through coughing and sneezing. Some, like smallpox, are transferred directly or indirectly by lesions, open sores, contaminated objects, or coughing. My personal favorites, strictly from an evolutionary standpoint of course, are those that covertly ensure their reproduction while we intimately ensure our own! These include the full gamut of microbes that trigger sexually transmitted diseases. Many sinister pathogens are passed from mother to fetus in utero.

  Others that germinate typhus, bubonic plague, Chagas, trypanosomiasis (African sleeping sickness), and the catalogue of diseases that are the concern of this book, catch a free ride provided by a vector (an organism that transmits disease) such as fleas, mites, flies, ticks, and our darling mosquito. To maximize their chances of survival, many germs use a combination of more than one method. The diverse collection of symptoms, or modes of transference, assembled by microorganisms is expert evolutionary selection to effectively procreate and ensure the existence of their species. These germs fight for their survival just as much as we do and stay an evolutionary step ahead of us as they continue to morph and shape-shift to circumvent our best means of extermination.

  Dinosaurs, whose long progeny lasted from 230 to 65 million years ago, ruled the earth for an astounding 165 million years. But they were not alone on the planet. Insects and their illnesses were present before, during, and after the reign of dinosaurs. First appearing some 350 million years ago, insects quickly attracted a toxic army of diseases, creating an unprecedented lethal alliance. Jurassic mosquitoes and sand flies were soon armed with these biological weapons of mass destruction. As bacteria, viruses, and parasites continued to insidiously and expertly evolve, they expanded their living space and real estate portfolio to include a zoological Noah’s Ark of animal safe houses. In classic Darwinian selection, more hosts increase the probability of survival and procreation.

  Undaunted by these behemoth dinosaurs, belligerent hordes of mosquitoes sought them out as prey. “These insect-borne infections together with already long-established parasites became more than the dinosaurs’ immune systems could handle,” theorize paleobiologists George and Roberta Poinar in their book What Bugged the Dinosaurs?. “With their deadly weapons, biting insects were the top predators in the food chain and could now shape the destiny of the dinosaurs just as they shape our world today.” Millions of years ago, also just like today, insatiable mosquitoes found a way to secure their blood snack—t
his buzz-and-bite happy meal remains unchanged.

  Thin-skinned dinosaurs, equivalent to modern-day chameleons and Gila monsters (both of which carry numerous mosquito-borne diseases), were ripe quarry for tiny, inconspicuous mosquitoes. Even the heavily armored beasts would have been vulnerable, since the skin flanked by the thick keratin (like our fingernails) scales of plated dinosaurs was an easy target, as was the skin of feathered, downy dinosaurs. In short, they were all fair game, just as birds, mammals, reptiles, and amphibians all are today.

  Think about our mosquito seasons, or your personal, often protracted, skirmishes with these tenacious enemies. We cover up our skin, we soak ourselves in repellent, we light citronella candles and burn coils, huddle around a fire, we swat and flail, and we fortify our positions with nets, screens, and tents. Yet, no matter how hard we try, the mosquito will always find the chink in our armor and nip our Achilles heel. She will not be denied her self-evident, unalienable right to procreate by way of our blood. She will target that one exposed area, pierce our clothing, and outmaneuver our best efforts to stymie her unrelenting assault and celebratory meal. It was no different for the dinosaurs, only they had no defensive measures.*

  Given the tropical, wet conditions, during the age of dinosaurs, mosquitoes would have bred and been active all year round, increasing their numbers and potency. Experts liken it to swarms of mosquitoes in the Canadian Arctic. “There aren’t a lot of animals for them to eat in the Arctic, so when they finally find one, they are ferocious,” says Dr. Lauren Culler, an entomologist at Dartmouth’s Institute of Arctic Studies. “They are relentless. They do not stop. You can be completely covered in a matter of seconds.” The more time reindeer and caribou spend fleeing the onslaught of mosquitoes, the less time they spend eating, migrating, or socializing, causing a severe decline in populations. Ravenous mosquito swarms literally bleed young caribou to death at a bite rate of 9,000 per minute, or by way of comparison, they can drain half the blood from an adult human in just two hours!

  Amber-encased mosquito specimens contain the blood of dinosaurs infected with various mosquito-borne diseases, including malaria, a forerunner to yellow fever, and worms similar to those that now cause heartworm in dogs and elephantiasis in humans. After all, in Michael Crichton’s novel Jurassic Park, dinosaur blood/DNA was extracted from the guts of amber-encased mosquitoes. CRISPR-like technology genetically engineered new living dinosaurs, creating a lucrative prehistoric theme park version of African Lion Safari. There is one small but important detail amiss with this script—the mosquito depicted in Steven Spielberg’s 1993 blockbuster movie adaptation is one of the few species that does not require blood to reproduce!

  Many of the mosquito-borne illnesses that afflict humans and animals today were present during the age of the dinosaurs and ravaged populations with deadly precision. A blood vessel from a T. rex revealed the unmistakable signs of both malaria and other parasitic worms, as does coprolite (petrified dinosaur dung) from numerous species. Mosquitoes currently transmit twenty-nine different forms of malaria to reptiles, although symptoms are absent or tolerable, as reptiles have built up an acquired immunity to this ancient disease. Dinosaurs, however, would have been void of such a shield, because at that time, malaria was a new recruit, joining the team of mosquito-borne diseases roughly 130 million years ago. “When arthropod-borne malaria was a relatively new disease,” hypothesize the Poinars, “the effects on dinosaurs could have been devastating until some degree of immunity was acquired . . . malarial organisms had already evolved their complicated life cycle.” Recently, when a handful of these diseases were injected into chameleons, the entire batch of test subjects died. While many of these diseases are not generally lethal, they would have been debilitating, like they are today. Dinosaurs would have been left incapacitated, sick, or lethargic, and vulnerable to attack or easy prey for carnivores.

  History does not warehouse well in neatly labeled boxes, for events do not exist in quarantined isolation. They exist on a broad spectrum, and all influence and shape each other. Historical episodes are rarely built on the ground of a single foundation. Most are the product of a tangled web of influences and cascading cause-and-effect relationships within a broader historical narrative. The mosquito and her diseases are no different.

  Take, for example, our dinosaur collapse model. While the dinosaur-disease extinction theory has gained traction and credibility over the last decade, it does not supplant or supersede the common and long-held earth-shattering-meteor collapse model. There is ample evidence and data from a breadth of scientific fields to indicate that a deep impact, leaving a crater the size of the state of Vermont, did occur 65.5 million years ago just west of Cancun in Mexico’s now touristy Yucatan Peninsula.

  Dinosaurs, however, were already in drastic decline. It is theorized that up to 70% of regional species were already extinct or endangered. The asteroid strike, with the subsequent nuclear winter and cataclysmic climate change, was the knockout punch, accelerating their inevitable disappearance. Sea levels and temperatures plunged and the earth’s ability to sustain life was harshly destabilized. “Whether a catastrophist or gradualist, you cannot discount the probability that diseases,” conclude the Poinars, “especially those vectored by miniscule [sic] insects, played an important role in exterminating the dinosaurs.” Long before the emergence of modern Homo sapiens, the mosquito was wreaking havoc and substantially altering the course of life on earth. Aided by her role in eliminating these top-tier dinosaur predators, mammals, including our direct prehominid ancestors, evolved and flourished.

  The relatively sudden disappearance of the dinosaurs allowed the few dazed but determined survivors to rise from the ashes to eke out an existence in a dark, unforgiving wasteland of wildfires, earthquakes, volcanoes, and acid rain. Patrolling this apocalyptic landscape were legions of heat-seeking mosquitoes. After the asteroid impact, smaller animals, many equipped with night vision, prospered. They required less food, were not finicky eaters, had more options for shelter from the raging inferno, and no longer had to fear for their safety. Two of the most adaptable groups to survive, thrive, and ultimately spawn a variety of new species were mammals and insects. Another was beaked birds, the only animal living today that is thought to be a direct descendant of dinosaurs. Given this unbroken family tree, birds harbored and disseminated numerous mosquito-borne diseases to a vast array of other animal species. Birds are still a primary reservoir for numerous mosquito-induced viruses, including West Nile and an assortment of encephalitides. Within this maelstrom of rebirth, regeneration, and evolutionary expansion, the ongoing war between man and mosquito was made.

  While dinosaurs perished, the bugs that aided in their demise endured to inject death and disease into humanity throughout our history. They are the ultimate survivors. Insects remain the most prolific and diverse catalogue of creatures on our planet, accounting for 57% of all living organisms, and an astounding 76% of all animal life. When compared to mammals, which comprise a paltry 0.35% of species, these numbers heighten the overall impact of insects. They quickly became asylums and the optimal hosts for various bacteria, viruses, and parasites. The sheer volume and variety of insects offered these microorganisms a greater chance for continued existence.

  The natural transmission of diseases from animals to humans is termed zoonosis (“animal sickness” in Greek) or more commonly referred to as “spillover.” Currently, zoonosis accounts for 75% of all human diseases, and is on the rise. The group that has seen the sharpest increase over the last fifty years is the arboviruses. These are viruses that are transmitted by arthropod vectors like ticks, gnats, and mosquitoes. In 1930, only six such viruses were known to cause disease in humans, with mosquito-borne yellow fever being by far the most deadly. The current total now stands at 505. Many older viruses have been formally identified, and new ones, including West Nile and Zika, made the swing from animal to human hosts through an insect vector, in this case the mosqui
to.

  Given our genetic similarities and common origin, 20% of our diseases are shared by, and transferred from, our ape cousins through various vectors, including mosquitoes. She and her diseases have stalked us through our evolutionary tree with dexterous Darwinian precision. Fossil evidence suggests that a form of the malaria parasite, which made its first appearance in birds 130 million years ago, plagued our primary human ancestors as early as 6 to 8 million years ago. It was precisely at this time that early hominids and chimpanzees, our closest relative with 96% identical DNA, shared a final common ancestor, and the humanoid line diverged from that of the great apes.*

  Our primordial malaria parasite companion shadowed both evolutionary lines and is currently shared by humans and all great apes. In fact, it is theorized that our hominid line gradually shed our thick fur to keep cool on the African savannah while making it easier to find and combat body parasites and biting insects. “Malaria, the oldest and cumulatively the deadliest of the human infectious diseases, seeped into our very earliest human history,” emphasizes historian James Webb in Humanity’s Burden, offering a sweeping account of the disease. “Malaria is thus an ancient and a modern scourge. For much of its career it left little trace. It sickened us in early epochs, long before we were able to record our experiences. Even in recent millennia, it has frequently lain silent in the diverse records of our pasts, too common a disease to claim much notice. At other times, epidemic malaria has careened violently across the landscapes of world history, leaving death and suffering in its wake.” Dr. W. D. Tigertt, an early malariologist at Walter Reed Army Medical Center, bemoaned, “Malaria, like the weather, appears to have always been with the human race, and as Mark Twain said about the weather, it seems that very little has been done about it.” Compared to mosquitoes and malaria, Homo sapiens is a new kid on the Darwinian block. It is generally accepted that we began our rapid ascent as modern Homo sapiens (“wise man”) only roughly 200,000 years ago.* At any rate, we are a relatively new species.