DEADLY CLIMATE

long!”), and now he is sorting out what he’s got. Soon these mosquitoes will be ground up and run through a series of tests to determine what, if any, pathogens they contain. There are millions of mosquitoes in Harris County. Every week, a few thousand are ground up to see if anything scary pops out. It’s not exactly sophisticated screening, but it’s more than most cities do.

Most of the mosquitoes in Vigilant’s pile belong to the Culex genus, ordinary backyard mosquitoes that are pretty much everywhere in the South. But Vigilant is looking for something else. He pokes through the pile, then plucks one out. At first glance, it looks the same as the others. He points out the bushy eyebrows, which is one way you distinguish a male from a female (this is a female). “See the white stripes on her abdomen?” he says to me, holding it under a big magnifying glass mounted on the desk. “She looks like she is wearing a white tuxedo.”

He holds her up like a prize, twisting her around so I can see her from every angle. “That’s Aedes aegypti,” he says. “She’s kind of beautiful, isn’t she?”

There are roughly 3,000 species of mosquitoes in the world. Of those, only a small percentage are of concern from a public-health perspective: Culex pipiens, which carries West Nile virus, and Aedes albopictus, also known as the Asian Tiger mosquito, which has recently arrived in the U.S. from Asia and can carry dengue and Zika, but does not lust after human blood like Aedes aegypti.

Aedes aegypti is an extremely competent vector for dengue and Zika, as well as yellow fever and chikungunya, making it one of most dangerous animals on Earth. But it is also one of the most companionable (or, as Fauci puts it, Aedes aegypti is “uniquely anthropophilic”). It’s the Labrador retriever of mosquitoes, happiest when it is living in or near our homes, laying eggs in little puddles of clean, fresh water in a bottle cap or the rim of a planter. And because it thrives in higher temperatures than other mosquitoes, it is well-adapted to life on a warming planet.

The impact of climate change on mosquitoes is fairly easy to model, in part because mosquitoes are very sensitive to temperature changes and will basically move to stay in their happy zone. And that happy zone is expanding. Aedes aegypti- transmitted diseases already cause more than 50 million infections every year worldwide, including in the United States, and cases have increased by thirtyfold in the past 50 years because of changes in climate, land use, and population. Mexico City, for example, has always been a few degrees too cold for Aedes aegypti to get established. Because of that, the city has always been blissfully free of yellow fever, dengue, and Zika, which have haunted the lowlands of Mexico. But now, as temperatures rise, Aedes aegypti is moving in. For the 21 million people who live in the city, it’s an alarming development. Wherever Aedes aegypti turns up, dengue, Zika, and other diseases are sure to follow. You can already see this happening in places like Nepal, which, until recently, was nearly free of mosquito-borne diseases. In 2015, Nepal had 135 cases of dengue. In 2019, there were 14,662 cases. Last summer’s dengue outbreak in Florida was fairly small, only about 60 cases (there were no fatalities), but it is a sign that the disease is gaining a foothold in the U.S. and could spread northward.

In other places, the changes in mosquito-borne diseases will be more complex. Malaria kills more than 400,000 people a year, mostly children in sub-Saharan Africa. The most deadly form of the disease is caused by the parasite Plasmodium falciparum, which is carried by the Anopheles gambiae mosquito, a smaller, less elegant creature than Aedes aegypti, and more sensitive to high temperatures. As the planet warms, West Africa is likely to grow too hot for Anopheles gambiae, which will shift to cooler regions in Eastern and Southern Africa. A recent study by Sadie Ryan, a medical geographer at the University of Florida, found that, under a high carbon-emissions scenario (which would cause more severe global warming), an additional 76 million people could be at risk from exposure to malaria transmission in Eastern and Southern Africa by the year 2080. At the same time, heat-loving Aedes aegypti will move into West Africa, vacated by Anopheles gambiae, putting millions of Africans at risk for dengue, Zika, and other diseases.

In Houston, as in most of the South, Aedes aegypti is established but less common. The city had its first outbreak of dengue in 2003, and a flare-up of Zika in 2016. Vigilant and other members of Harris County Mosquito Control are constantly on the lookout for Aedes aegypti, knowing they are harbingers of doom. Their only real tool to fight them is to spray insecticides, which they do from the back of pickup trucks whenever there is evidence of a flare-up. But Aedes aegypti, as well as other mosquitoes, are developing immunity to many commercial insecticides. “We are losing the war,” says Galveston lab director Scott Weaver. Technological advances, such as genetically engineering mosquitoes to produce female offspring that are infertile, may hold some promise in the future, but right now Aedes aegypti reigns supreme as the most insidious and unstoppable vector of future diseases. As Anthony Fauci wrote, “Any virus that can efficiently infect Aedes aegypti also has potential access to billions of humans.”

The galveston national laboratory is a fortress of pathogens, although you would never know if from the outside. It sits on the campus of the University of Texas Medical Center like any other building. There are some concrete barriers on the outside, and a bunch of weird-looking exhaust systems on the roof, but otherwise, it could easily be the building where you took Chemistry 101 in college. Inside, in one of about a dozen Biosafety Level 4 labs in the United States, scientists work on some of the most lethal viruses in the world: Ebola, Nipah, Marburg, and others.

The BSL-4 lab is Dennis Bente’s workroom. A broad-shouldered guy with a full dark beard and a slight German accent, Bente grew up in a small town in northwest Germany and studied veterinary medicine in Hannover before developing an interest in vector-borne diseases. He worked with mosquitoes for a while, then decided ticks were more compelling.

The BSL-4 lab is basically a big concrete box within the larger lab. Entering it is like a journey into deep space. Bente first passes through a buffer corridor, where he grabs a clean pair of scrubs. Then he enters a changing room, where he strips off his street clothes and pulls on the scrubs. Next is the suit room, where he steps into what he calls his “space suit,” including built-in gloves and a clear plastic helmet. To pressurize the suit, and give himself air to breathe, Bente hooks up to an air hose and inflates like the Michelin Man. If all is well, he steps into the air lock, which is the most important barrier between the deadly pathogens and the outside world. He opens a heavy, airtight submarine door, closes it, walks a few feet, then opens another heavy, airtight submarine door. Finally, he steps into the hot zone.

Inside, he works with a group of ornate-looking ticks that are native to the Mediterranean basin, known as Hyalomma ticks. They are brown, with yellow stripes on their legs, which are much longer than the stubby legs on deer ticks you see in Upstate New York. They look almost spidery, which is not surprising — ticks are arachnids, not insects, in the same family as spiders and scorpions. With their long legs, Hyalomma ticks are the speed demons of the tick world. (On YouTube, you can find videos of Hyalommas running after people like tiny lions in pursuit of an antelope.) Unlike many other ticks, Hyalommas are predators. They are one of the few species of ticks that have eyes (the word “Hyalomma” is derived from the Greek words for “glass” and “eye”). Instead of using CO2 sensors like other ticks to locate a blood meal, Hyalommas sense vibrations in the ground, and watch for shadows, to chase down a nearby human (or livestock, one of their favorite foods).

But Bente is not studying Hyalomma ticks because of their athletic ability or visual acuity. He is studying them because they are the most competent carriers and transmitters of Crimean Congo Hemorrhagic Fever (CCHF) to humans. One way to think about CCHF is it’s basically a slightly less awful version of Ebola. CCHF often starts with high fever, joint pain, and vomiting. Red spots appear on your face and throat. Then by the fourth day, you get severe bruising and nosebleeds, and in many cases, uncontrolled bleeding from other orifices. It lasts for two weeks or so. There is no treatment, no vaccine, no cure. The fatality rate for people with CCHF ranges from about five percent to 30 percent.

Right now, as far as Bente knows, the only Hyalomma ticks in America are in the Galveston lab. In the wild, they are found in North Africa, Asia, and parts of Europe (in Turkey, there are about 700 CCHF cases a year). The ticks, which thrive in warm, dry climates, are expanding their range. In recent years, CCHF has killed people in Spain and northern India.

Bente keeps a colony of Hyalomma ticks in his lab and feeds them on mice and rabbits that he deliberately infects with the CCHF virus. (“The virus has no impact on these animals,” Bente points out. “It’s only dangerous to humans.”) He is studying fundamental questions about Hyalomma ticks and CCHF that should freak out anyone who’d like to walk through nature without worrying whether they’ll contract a virus that will make their eyeballs bleed: Can Hyalomma ticks be established in the U.S.? (It’s extremely unlikely.) Might other types of ticks be carrying

“I don’t like the narrative that says we are one tick bite away from catastrophe,” says a researcher. “At the same time, I can’t say it won’t happen.”

CCHF in Africa? (Yes, but so far, they are only “a sideshow,” Bente says). Is airborne transmission of CCHF possible? (“CCHF is a very old virus,” Bente says. “Why mutate now?”) But Bente still has concerns.

As disease vectors, ticks are very different from mosquitoes. They live up to two years instead of a few weeks. But like mosquitoes, they are sensitive to changes in temperature and can’t survive long in cold or dry climates. As the world warms, they are following the heat. Some tick species are moving as much as 30 miles north each year — an unseen parade of bloodsuckers conquering new terrain. They are difficult to target with insecticides, and have many remarkable survival tricks, such as the ability to go long periods without water by basically spitting into a pile of leaves and then drinking it later when they are thirsty. Heat is also changing ticks’ appetites. A recent study found that as temperatures rise, brown dog ticks that transmit Rocky Mountain Spotted Fever — a disease with a four percent fatality rate — are twice as likely to choose to bite people over dogs. In the U.S., ticks can carry more than 20 different pathogens — and more are being discovered all the time. “The more we look at ticks, the more viruses we continue to find,” says Bobbi Pritt, a microbiologist at the Mayo Clinic in Rochester, Minnesota.

Lyme disease is emblematic of the threat ticks pose in a warming world. It is caused by deer ticks carrying the bacteria Borrelia burgdorferi. Lyme was discovered in Connecticut in the mid-1970s. Today it is a major, and growing, health threat. According to the CDC, reported cases in the U.S. have tripled since the late Nineties. Lyme disease has become an almost “unparalleled threat to regular American life,” as Bennett Nemser, an epidemiologist who manages the Cohen Lyme and Tickborne Disease Initiative at the Steven & Alexandra Cohen Foundation, has said. “Really anyone — regardless of age, gender, political interest, affluence — can touch a piece of grass and get a tick on them.”

It’s not just the heat that has expanded the range of Lyme-carrying ticks. It’s also the increasingly fragmented landscapes in the Northeast. As forests are cut up into suburban developments, the populations of foxes and owls decline, which leads to an explosion in the population of white-footed mice, which are the main reservoir for Borrelia burgdorferi. Young larval ticks feed on the infected mice, and then pick up Lyme and later spread it to anyone passing by.

But in Bente’s view, the most worrisome development in TickWorld is the invasion of Asian longhorned ticks in the U.S., which he calls “a cautionary tale.” Nobody is quite sure how or when the first Asian longhorned tick (a.k.a. Haemaphysalis longicornis) arrived in the continental U.S. They are native to East Asia, including Australia and New Zealand. They were first reported in 2017, in New Jersey. Within a year, researchers had found the tick in eight other states, and its territory continues to expand. One key contributor to its rapid spread is the fact that females can reproduce through cloning themselves, without the need for mating, a process called parthenogenesis. This makes it extremely hard to control. “In practice, it’s impossible to eradicate this species,” says Illa Rochlin, an entomologist at Rutgers University.

Asian longhorned ticks are aggressive biters, and can gang up on prey to drink large quantities of blood. Their preferred meal is cattle. In parts of New Zealand and Australia, the ticks have reduced production in dairy cattle by 25 percent. So far, there is no evidence that Asian longhorns in North America have transmitted diseases to humans. But that could change. Pritt calls the longhorned invasion “extremely worrisome.” They can carry several deadly human pathogens, including potentially fatal severe fever with thrombocytopenia syndrome (SFTS) virus and Rickettsia japonica, which causes Japanese spotted fever. “While these pathogens have yet to be found in the United States, there is a risk of their future introduction,” Pritt told me.

A close cousin of SFTS, as it turns out, is CCHF. What worries Bente is the possibility of what scientists call “vector switching.” That is, that somehow the CCHF virus jumps from Hyalomma ticks, which are not yet in the U.S. outside of Bente’s lab, to Asian longhorned ticks, an aggressive biter that is becoming widespread.

Could CCHF make the leap to Asian longhorned ticks? “Nature is complex,” Bente tells me. “I don’t like the narrative that says we are one tick bite away from catastrophe. But at the same time, I can’t say it won’t happen.”

Iask max vigilant to show me the most mosquito-infested neighborhood in Houston, the place where, if dengue or Zika or some other virus were to emerge, people would be most at risk. We leave the mosquito control center and drive (in separate vehicles, due to Covid) 30 blocks or so into a mostly black and Hispanic neighborhood with flatroofed homes. At the time, Covid was raging, the streets were empty, hospitals were at max capacity, and the fourth-largest city in America felt like a ghost-town. We park at a nondescript intersection and get out and stand across from a lot with abandoned cars and a motorcycle propped up on a milk crate, missing its front wheel. There is a lot of green — long-limbed oaks, shaggy palms, uncut grass. My first thought is, if I were a microbe, this would be a good place to hide. My second thought is, poverty. I notice a ripped window screen on a house nearby. And despite the heat, I hear no hum of air conditioning.

“This is mosquito heaven,” Vigilant says. He points to a drainage ditch near the side of the road where mosquitoes could spawn, to all the greenery, where they could rest in the shade during the day, and the easy access to human blood, through the ripped screens and open windows. “It reminds me of my home in Dominica.”

Among public-health officials, scientists, and philanthropists concerned about the new pandemic era, there is much talk about the need for preparedness. “We need a global disease-surveillance system,” says Mark Smolinski, the president of Ending Pandemics, a nonprofit that is engaged in eight countries to deploy cellphone and other simple technology to allow people to notify public-health officials of suspicious outbreaks. In the U.S., there have been ambitious federal programs, including PREDICT, which was designed to detect and help prepare for new outbreaks. It started in 2009 as part of the Obama administration’s Emerging Pandemic Threats program, inspired by the 2005 H5N1 bird-flu scare. PREDICT spent more than $200 million to train about 5,000 scientists in 30 African and Asian countries, and to build or strengthen 60 laboratories to help detect animal viruses that could endanger humans. Scientists working for PREDICT collected more than 160,000 biological samples and found nearly 1,000 new viruses, including a new strain of Ebola. But the Trump administration wasn’t interested in continuing any program that contributed to the greater global good, especially if it had been set up under Obama. Funding ran out in October 2019, just a few months before the Covid-19 pandemic hit. Last April, the Trump administration granted the program an emergency extension, but by then it was too late. President-elect Biden has promised to relaunch PREDICT, as well as restore the White House National Security Council Directorate for Global Health Security and Biodefense, which the Trump administration had folded into another organization in 2018. Biden’s new chief of staff, Ron Klain, is widely respected for his role as Obama’s “Ebola czar” during the outbreak of the virus in Africa in 2015, and will surely put the White House on a wartime footing against Covid.

But standing on that forlorn street in the fossilfuel capital of the world made it clear to me that a lack of disease surveillance is not the main problem. The main problem is how we live. We mow down forests to build suburbs and raise cattle in meat factories and power our homes and cars with fossil fuels that are heating the planet and upending the natural world. As Dr. Aaron Bernstein, the interim director of the Center for Climate, Health, and the Global Environment at Harvard’s T.H. Chan School of Public Health, put it: “If you wanted to do something to prevent disease emergence, first of all we need to seriously reconsider how we do business with the biosphere. We can’t simply pretend that we can extract things and put species in assortments that they’ve never been in before, and hope that somehow doesn’t lead to disease emergence.”

And it’s not just new diseases. Climate change will also increase our vulnerability to old ones. Food production in some of the most desperate regions of the world will decline due to increased heat and drought. “The biggest impact climate change has on human health is likely to be the rise in common diseases like tuberculosis and measles in malnourished people in places like Ethiopia and Mali,” says Stanford’s Stephen Luby. “When people are starving, they are more vulnerable to bacteria and viruses.”

In Texas, the first state to hit 1 million cases of Covid-19, better disease surveillance would not have changed anything. People were practically dropping dead in the street from the virus, and still you could wander through a medium-size town in the state and not see a single person wearing a mask. Texas Gov. Greg Abbott, a staunch Republican, clashed with mayors and county judges over their authority to shut down businesses and enforce face-mask orders. The people who suffered most, as always, were poor people, people of color, people without health insurance, people on the margins of our high-tech fossil-fuel-powered society. In the end, pandemics are a political problem, not a scientific one.

But the fight continues. After we talk for a few minutes, Vigilant grabs a pickax out of the back of his truck. He walks over to a manhole cover in the middle of the street, sticks the pick into a hole, and muscles it open. Dangling from the underside of the cover is a mosquito trap. A canister of dry ice and a light dangles from a chain, with a mesh container at the bottom. The light and the CO2 from the dry ice attract the mosquitoes, and the mesh traps them inside. If there is a new microbe in town, there’s a decent chance it will show up here.

Vigilant unhooks the trap and holds it up so I can see the mosquitoes. There are hundreds of them, buzzing around, each one its own package of pathogens, each one potentially carrying a virus or parasite that humans have never encountered before. Maybe the new pathogen doesn’t survive the leap to humans. Or maybe it takes hold, replicates a few billion times, and changes the course of civilization.