Jeff Goodell writes:

Jennifer Jones spent most of her summer at home, as so many of us did, trying to avoid the plague. Jones, 45, lives in Tavernier, a community in the Florida Keys just south of Key Largo, and passed a lot of time in her yard, puttering around with plants. At some point, a mosquito landed on her. That’s not unusual in Florida, and Jones doesn’t remember this mosquito bite in particular. But it was not a garden-variety backyard mosquito. It was Aedes aegypti, an exquisitely designed killing machine that is one of the most deadly animals in human history. By one count, half the people who have ever lived have been killed by mosquito-borne pathogens. Aedes aegypti, which first arrived in North America on slave ships in the 17th century, is capable of carrying a whole arsenal of dangerous diseases, from yellow fever to Zika.

The mosquito could sense the heat of Jones’ body and smell CO2 on her breath from more than 30 feet away. It landed on her exposed flesh, likely her arm or lower leg. The mosquito was a female — only females drink blood, which they need to produce their eggs. It worked quickly, knowing, in the genetic coding of its insect brain, that the longer it lingered the less likely it was to survive. First, it spit on Jones’ skin to numb it so she wouldn’t be alerted to the bite. Then it plunged its syringe-like proboscis, which is actually a sheath containing six needles, into Jones’ skin. It probed around until it found an ideal place to tap into a blood vessel. Then it inserted two needles, each one serrated like a carving knife, to saw a hole in Jones’ flesh. Two more needles pried the hole open, which allowed it to insert what looks like a tiny hypodermic syringe into Jones’ blood vessel. And here is the important part: As it sucked out the blood, the mosquito spit its own saliva into Jones’ veins, which contains an anticoagulant that prevents the blood from clotting at the puncture site. In this case, it also contained a virus that causes a tropical disease called dengue fever. When its appetite was sated and its belly full of blood, the mosquito flew off.

The word “dengue” most likely comes from the Swahili phrase “Ka-dinga pepo,” meaning “cramp-like seizure caused by an evil spirit.” Dengue is also known as “breakbone fever” because it feels like your bones are breaking when you have it. It has been around for centuries, and is most common in Asia and the Caribbean. According to the World Health Organization, before 1970, only nine countries had severe dengue epidemics. Since then, it has increased thirtyfold, making it endemic — that is, permanently embedded in the local mosquito population — in 128 countries. The WHO recorded 4.2 million cases of dengue in 2019. As the world warms, making more of the planet comfortable for heat-loving Aedes aegypti, the mosquito’s range will expand northward, and to higher altitudes. By 2080, one recent study estimated, more than 6 billion people, or 60 percent of the world’s population, will be at risk for dengue. “The fact is, climate change is going to sicken and kill a lot of people,” says Colin Carlson, a biologist at the Center for Global Health and Security at Georgetown University. “Mosquito-borne diseases are going to be a big way that happens.”

It took a week or so for the virus to do its work. Once in Jones’ bloodstream, it latched onto her white blood cells and began replicating. She was watering plants when she felt lightheaded, and then developed a fever. “I knew something weird was going on,” she tells me. Rashes. Pain behind her eyes. And bone-break ache in her joints. “I felt like I was a 99-year-old lady who had been hit by a truck,” she says. In rare cases, dengue can escalate to brain swelling and bleeding, which can be fatal (about 10,000 people a year die from dengue). But Jones was lucky. The pain and fever faded after four or five days, and she was almost recovered when her son called her to his room to point out the red splotches on his skin. As soon as she saw them, she knew: dengue.

As it turned out, the Florida Keys, already hit hard by the coronavirus, was in the middle of a dengue outbreak too.

Covid-19 likely emerged from the wilds near southern China, then found residence in horseshoe bats before making the jump to humans. The virus, as of this writing, has infected 63 million people and caused 1.5 million deaths around the world. The global economic impact of the pandemic was estimated at $8 trillion to $16 trillion in July 2020 — it may be $16 trillion in the U.S. alone by the fourth quarter of 2021 (assuming vaccines are effective at controlling it by then). The amount of human suffering this tiny microbe has caused is incalculable: lost loved ones, vanished jobs, broken families, and lingering sickness from a virus that will eventually retreat but will never disappear.

And yet we got lucky. “It could have been much worse,” says Scott Weaver, director of the Galveston National Laboratory in Texas, one of the top viral-research centers in the country. Compared with other pathogens out there, Covid-19 is relatively docile. It is an easily transmissible virus that is far more deadly than the flu, and has mysterious long-term effects. But it doesn’t kill three out of four people it infects, like the Nipah virus. It doesn’t cause people to bleed out of their eyes and rectums like Ebola. “Imagine a disease with 75 percent case fatality that is equally transmissible,” says Stephen Luby, an epidemiologist at Stanford University. “That would be an existential threat to human civilization.”

The Covid-19 pandemic is often compared to the 1918 influenza, which killed at least 50 million people globally. But it is perhaps more accurately seen as a preview of what’s to come. “We have entered a pandemic era,” wrote Dr. Anthony Fauci of the National Institute of Allergy and Infectious Diseases in a recent paper he co-authored with his NIAID colleague David Morens. The paper cites HIV/AIDS, which has so far killed at least 37 million, as well as “unprecedented pandemic explosions” of the past decade. It’s a deadly list, starting with the H1N1 “swine” influenza in 2009, chikungunya in 2014, and Zika in 2015. Ebola fever has burned in large parts of Africa for the past six years. In addition, there are seven different known coronaviruses that can infect humans. SARS-CoV spilled over from an animal host, likely a civet cat, in 2002–03, and caused a near-pandemic before disappearing. Middle East respiratory syndrome (MERS) coronavirus jumped from camels to people in 2012, but never found a way to spread efficiently among humans, and died out quickly. Now we have SARS-CoV-2, the virus that causes Covid-19. [Continue reading…]