The thing Que Lan remembers best about the summer of 1973 is the uncontrollable shaking. A stifling blanket of humid air had settled on top of Wuhan, the capital of Hubei province in central China, and it sat on the near 100-degree days like a deflated cloud. It was the time of year when a city collectively dreams of a sudden rain shower or a cool breeze—and yet 13-year-old Lan lay shivering underneath three blankets as her disease dragged her from profuse sweating into debilitating chills.
The diagnosis had surprised Lan. Malaria seemed like a far-off threat, the scourge of rural areas dotted with rice paddies and infested with mosquitoes. But even in the metropolitan climes of central China’s biggest city, where government trucks rolled down the avenues dousing neighborhoods with DDT, the threat of the disease was never too distant. As everywhere in the tropical and subtropical regions of Earth—where nearly 50 percent of the world’s population now lives—malaria lurks just one fateful bite away.
Lan’s illness was one of roughly one-half billion cases of malaria around the world in 1973. Because her family had easy access to medications, she avoided a far more somber statistic: More than a million people die from malaria every year, most of them children. Instead, Lan endured two weeks of shivering, fevers and aches and then recovered, well enough to return to school. Malaria was finished with her.
But Que Lan was not finished with malaria.
Now, nearly four decades after the bell first rung in her bout with the disease, Lan is halfway across the world, preparing to land her first solid blow. Malaria has not gone away and is as menacing as ever. While the disease has been pushed out of more temperate (and more prosperous) areas like Europe and the United States, malaria is still present in 108 of the world’s 195 countries. In most years, more than 250 million people will get sick with malaria and one million—most of them children—will die. Those statistics have led groups such as the Bill and Melinda Gates Foundation to declare all-out war on malaria, making eradication of the disease its number one medical goal. The World Health Organization and National Institutes of Health are equally engaged in the fight. But while these scientists and public-health officials struggle to control the disease and its devastating effects, Lan, a CALS associate professor of entomology, is attacking the source—the six-legged pest that malaria uses to get around.
Entomology has come a long way from the days of peering through magnifying glasses at anthills. Today, entomologists like Lan peer at bugs from the inside out, scouring their genes for the drivers of their behavior. In her office on the eighth floor of Russell Labs, Lan hunches over her office computer and motions for a colleague to take a look at the bright bands of color on the screen. The bands are genetic code and, from that code, Lan has teased out a single gene essential to mosquito survival. A weakness. A genetic chink in the armor. In a multi-year study funded partly by the U.S. Department of Defense—which hopes to find better mosquito-control methods to protect troops in tropical regions—she’s also found a way to prevent that gene from doing its job. This is the target her lab is aiming for, a promising new approach in the fight against malaria. She’s out to debug the bug.
Humans have been swatting at mosquitoes for millennia. And mosquitoes have returned the favor, injecting us with all sorts of diseases, from dengue fever to lymphatic filariasis to West Nile virus. But malaria is king of them all, a harbinger of death and disease throughout the ages. Descriptions of malaria symptoms can be found in ancient Chinese medical writings dating back to 2700 B.C. and are scattered throughout Greek and Roman texts. The disease has claimed millions upon millions of lives, including those of several popes, the Italian poet, Dante, and, some scholars believe, Alexander the Great. Outbreaks of malaria have sent famous explorers far off course and swung the outcomes of wars by incapacitating entire armies.
As is to be expected with such a devastating disease, we’ve spent centuries battling back. In ancient China, a remedy for malaria’s intense fevers was made from dried wormwood leaves. In the 17th century, it was bark from the Cinchona calisaya tree that grew high in the Peruvian Andes. The active ingredients from both remedies are still used today in some malaria drugs. Other anti-malarial drugs were developed during both World War II and the Vietnam War as prosperous nations searched for ways to minimize the effects of malaria on their forces. Today, travelers to malaria-afflicted regions can take any of a half-dozen drugs to prevent infection and treat symptoms. But the development of new drugs has slowed dramatically, and the old ones are growing less effective as the disease gains resistance to them.
When a mosquito infects a person with malaria, they are actually injecting the plasmodium parasite into the bloodstream. Plasmodium heads for the liver where it begins to reproduce. It eventually builds an army of parasites that swarm into the bloodstream where they kill red blood cells and, sometimes, their host. During this stage of the disease, a single person can have millions upon millions of plasmodium parasites reproducing in their body. Multiply that single infection with hundreds of millions of people also carrying hundreds of millions of plasmodium parasites, and resistance to commonly used drugs is an inescapable result. To stay ahead of malaria means keeping it on its toes. Researchers know that the war will not be won with World War II-era weapons. It will take a modern, multifaceted arsenal to keep pace.
This is a lesson that the World Health Organization learned the hard way. In 1955, the WHO announced its Global Malaria Eradication Programme, aiming to rid the world of the disease with the help of newly developed weapons—including anti-malarial drugs developed during World War II and the insecticide DDT—and some it hoped were on the way. Medical science believed a vaccine to ward off malarial infection was close at hand, and buoyed by that optimism, the WHO boldly predicted the tropics could be soon free from the grip of the disease. But while the campaign did push malaria out of temperate regions of the United States and Europe, the disease proved intractable in other areas. A vaccine did not emerge, and the parasite quickly evolved resistance to many of the new drugs. But the WHO’s biggest shortcoming was underestimating the complexity of eradicating such a disease. That kind of bold aim necessitates more than good medicine.
“With malaria, we have pretty good drugs,” says Bruce Christensen, a parasitologist in the UW School of Veterinary Medicine.. “The problem is you don’t have very good infrastructure for health facilities (in developing nations). So it’s really hard for people to even get medical care. So even if you have good drugs, you probably don’t have them in the areas where you need them.”
At every turn, the WHO’s efforts were thwarted by the realities of human nature. People didn’t use the bed nets that were handed out in villages to prevent mosquito bites because the nets were stifling to sleep under and were handy as fishing nets. A campaign to spray the walls of houses with DDT met with a similarly unexpected failure. “One of the big problems they had with their workers was they would leave one wall unsprayed,” says Christensen. “And the reason they did that is because if they sprayed all the walls and killed all the mosquitoes, then they were out of a job and this was the best job they’d ever had.”
DDT presented other problems, as well. The insecticide had been the go-to weapon for mosquito control since 1948, when Paul Mueller won a Nobel Prize for demonstrating its lethal power over insects. By the 1960s, however, the pesticide once hailed as a miracle was looking more like an environmental monster, laying waste to birds, frogs and other animals. Facing mounting criticism from conservationists, the U.S. Environmental Protection Agency banned its use in 1972. With no U.S. market to serve, many companies stopped manufacturing DDT, making it scarcer and more expensive for widespread applications in the tropics. Plus, after three decades of near-exclusive use, it, too, was losing its potency.
In 1973—the same year that Que Lan was shivering under her blankets and unknowingly preparing for a career doing battle with malaria—the WHO threw in the towel. Malaria, the organization admitted, was hopelessly entrenched in certain parts of the globe.
The failure of eradication triggered a shift in thinking about malaria control. Many scientists and public-health officials realized that malaria and mosquitoes went hand in hand. You could never kill the disease, without also going after its carrier. In his 2010 letter to Gates Foundation supporters, Bill Gates even acknowledges that modern medicine isn’t ready to eliminate malaria. A vaccine, he says, is at least ten years away. We have to get better at killing mosquitoes.
The approach, called vector control, sounds hopeless at first. Places where malaria is endemic are home to multiple millions of mosquitoes that thrive year-round.No method of insect control could possibly eliminate that kind of population.Papua New Guinea is a perfect example, says Bruce Christensen. Mosquitoes there often lay their eggs in puddles of rainwater that collect in cattle hoof prints. Multiply a hundred eggs by a million hoofprints and the numbers quickly become incomprehensible. “What do you do?” Christensen asks. “Do you try to put [pesticide] everywhere? Because there are breeding sites everywhere.” The best that can be hoped for is to knock mosquito populations back, especially around areas more densely populated with people.
The authors of a new report on malaria control say such modest efforts may actually produce major results. . Published in the August issue of PLoS Medicine, the article points out that in parts of sub-Saharan Africa, a person can receive up to one thousand infectious bites from a malaria-carrying mosquito each year. Those mosquitoes aren’t just injecting that person with the disease, they are often also picking up a new batch of the parasite to carry to someone else. That means that, even if a massive campaign of drug delivery pushed the malaria to the brink of regional extinction, a single infected person moving in to the area could give rise to thousands of new infections and quickly re-establish the disease.
Controlling mosquitoes, on the other hand, makes it more difficult for the disease to rebound from successful anti-malaria campaigns. Reduce the number of mosquitoes in a malaria-infected environment by just half, and the instances of multiple infections and transmissions can drop by entire orders of magnitude. You simply can’t overestimate the role mosquitoes play the authors conclude. And that means that, to wage a truly effective campaign against malaria you need more than a doctor. You need an exterminator.
After her bout with malaria, Que Lan went on to study the sciences. She studied microbiology at Wuhan University in China and earning a master’s degree at Brock College in St. Catharine’s, Ontario. But it took one intriguing offer—an invitation to complete her doctoral work at the University of Minnesota in noted entomologist Ann Fallon’s mosquito lab – for Lan to realize that the mosquito that bit her in 1973 was still buzzing around in the back of her head. It seemed like a crazy idea, the bravado of young ambition, but Que Lan wanted to bite back “I thought maybe someday I can do something about this,” says Lan, laughing at the audacity of her younger self. “It was just this kind of remote idea (that) maybe someday I can do something (to help).”
Under Fallon’s tutelage, Lan learned molecular biology, which she says “was really nothing to do with killing mosquitoes,” Her research had more to do with what makes them thrive. But after joining the UW-Madison faculty in 2000, she set out to turn that knowledge into better weapons for mosquito control.
“The key,” she says, “is to really understand the biology of your target insect and develop specific components that just target that.”
Lan knew from her Ph.D. work that mosquitoes, like all arthropods, don’t make their own steroids or cholesterols. Both substances are essential for survival, and insects must get them from their food sources. So when Lan discovered that a gene called sterol carrier protein-2 was activated in proteins in the gut during feeding, she knew she had found an essential link in a mosquito’s ability to live. “That’s the Achilles’ heel,” she says. “(I thought) if I can destroy this pathway, they may not survive.”
Her lab turned their focus exclusively on the gene. They mapped its proteins to decipher the chemical transactions that took place around the gene and studied when and where it was switched on. They studied the function of the gene during the mosquito’s various development stages, which led to a critical discovery: If the gene was not allowed to activate inside a mosquito egg, the developing larva would not get the cholesterol it needed and the egg would not hatch. In other words, silence the gene and you silence the bug.
The finding was a career-defining achievement in itself. Researchers often only get this far—learning something new that hasn’t been known before. But Lan wanted more. She knew the finding represented an exploitable weakness, one that could be developed into a method of control. Imagine, for example, dropping a pellet into a pool of standing water, where mosquitoes lay their eggs, that would deliver a knock-out blow to the eggs’ cholesterol-uptake capacity. Although her focus had been on mosquitoes of the species aedes egypti, which carry yellow fever, Lan was confident it would work for malaria- and West Nile-transmitting mosquitoes, as well. The idea of those little pellets preventing a disease-carrying swarm from hatching, Lan says, “is really satisfying.”
But what would flip the switch? Lan needed a chemical that could knock the gene out of order. And that chemical needed to pose as little threat to humans, animals or the environment as possible. The last thing she wanted was to create another DDT. To avoid this, she took a trip to see a few robots on the west side of campus.
Housed in the Paul P. Carbone Comprehensive Cancer Center at the UW-Madison School of Medicine and Public Health, the Small-Molecule Screening Facility allows researchers to conduct thousands of experiments simultaneously. The facility boasts three robots that store tens of thousands of chemicals. Introduce those robots to a cell line or protein, and they’ll introduce it to a few molecules of every chemical at their disposal. Advanced and sensitive instruments monitor each experiment and alert researchers when there’s a “hit,” or, rather, when one chemical has achieved its desired results. And that’s what happened when Lan’s lab took sterol carrier protein-2 for run through the robot gauntlet: Out of tens of thousands of chemicals, they found a dozen that worked. And they all worked in much the same way. Like a game of molecular musical chairs, these synthetic chemicals competed with cholesterol for a seat on sterol carrier protein-2. For every molecule of the chemical that bound to the protein, a cholesterol molecule was out of luck. Lan left the facility with a plan—introduce enough molecules of the chemical to the game, and developing mosquitoes don’t get enough cholesterol to ever hatch from their eggs.
The trouble with synthetic chemicals, though, is that they hang around in the ecosystem long after they’ve been applied. If Lan’s chemical tool were going to see wide use, a better alternative would be to employ a natural chemical to muck with the bug’s genes. So Lan again turned to the library to find a natural chemical that mimicked the activity of the synthetics.
The source was unexpected—an Asian fruit called mangosteen, which contains a chemical that turns out to be a dead ringer for the best-performing of the synthetic chemicals Lan tested. Touted for the rejuvenating power of its juice, mangosteen is called “queen of the fruit” in parts of Southeast Asia. The fact that a malaria-infested country could harbor a promising new natural agent against the disease is a delicious irony, Lan finds.
“We’re pretty sure this quality is one of (mangosteen’s) main evolutionary traits. It’s a naturally occurring defense compound,” she says. “We would never have imagined to use (mangosteen extract) on insects. Not in a million years if we didn’t get it from our library screening.”
Susan Paskewitz, a CALS entomology professor who also works on mosquito-borne disease, thinks there’s great promise in this new way of methodically developing insecticides. “In the old days we might have started with something that from lab experiments was known to kill agricultural pests and then tested it on mosquitoes,” she says. The power of genetics is to look at species-specific approaches, which could mean fewer unintended consequences.
And that seems true for Lan’s genetic attack strategy. Since the chemical approach employs a different mode of action than traditional pesticides, it promises to be effective against species that have grown resistant to those applications. There’s also little danger of the chemical affecting humans or other animals since chemicals bind differently in our DNA. And even if some of the chemicals bound and prevented uptake of cholesterol, it wouldn’t matter much since vertebrates make their own cholesterol.
Lan has taken this particular avenue of research as far as she can as a researcher. Her naturally derived cholesterol inhibitor has been submitted for a patent, and she’s now waiting to hear if industry will license the technology and develop a commercial product from it. She knows her find is not the “answer” to the malaria question. But she is convinced it will be a welcome addition to the fight.
“The toolbox is almost empty,” she says. “We’re just putting more tools into the toolbox.”
Of course, Lan knows her new tool won’t last forever. Someday the compound will grow obsolete as mosquitoes slowly evolve resistance. But she is confident science will uncover new weaknesses in mosquitoes’ makeup and reveal new routes of attack.
“You’re never going to win,” she says. “(Mosquitoes) have been around for millions of years, and they’re going to be around for another million years. We just try to avoid their contact (with humans) in high-density populations. That’s all we can do.” But, mosquitoes, beware. Just because she knows she can’t win, doesn’t mean Lan isn’t going to fight. As long as little girls shiver under heavy blankets in the sweltering heat, she won’t give up. What that mosquito started back in 1973, Lan will never finish.This article was posted in Biotechnology, Environment, Fall 2010, Features, Health, Medicine and tagged Entomology, Global health, Insects, mosquito.