Building a Better Mosquito
Every day, Nijole Jasinskiene walked down a basement hallway and pulled open a tightly sealed door to the laboratory equivalent of a New Orleans summer. Warm, moist air blew past her as she stepped inside and yanked the door shut.
She made her way over to hundreds of white cups holding mosquitoes that had given birth to larvae, which wriggled in trays nearby. For two weeks, Jasinskiene peered into the trays. The larvae were growing. Soon they, too, would be adults. Then she could examine them to see if, finally, after nearly a decade of trying, they looked back at her with red eyes.
The previous “red eye” experiment at UC Irvine’s microbiology center had been a disaster. Lab assistants working under high-power microscopes had taken 1,000 mosquito eggs the size of poppy seeds and pierced them with custom-made, ultra-fine glass needles, then injected them with genes in hopes of producing red-eyed mutant adults. Only a frustratingly small number made it to adulthood, and there was nary a red eye among them.
But experimental science is almost all failure, until the moment of breakthrough. So the team of researchers, led by UC Irvine geneticist Anthony James, mounted another try. Though their efforts to color the eyes red would have no great purpose in itself, it would serve the highly significant step of indicating that scientists had found a way to break into the genetic code of mosquitoes.
James and his assistants knew they were close. They went back to their microscopes and eggs, working more slowly, trying to reduce even more the damage they did to the eggs. Perhaps their delicate touch made the difference. Perhaps it was plain luck. Regardless, as the creatures emerged, several of them turned beady little red eyes to the world.
So far, so good. But the real trick was to make the change a lasting one. For that, the team needed to see if the altered mosquitoes could make red-eyed babies. So it was back to the insectary, the windowless insect-breeding room equipped with heaters and humidifiers turned up so high that water condenses on the ceiling and falls in a steady drip.
Male and female mosquitoes were placed in the covered paper cups. After copulation, the females required blood to nourish their eggs, so mice were anesthetized and laid on the mesh covers of the cups. The mosquitoes gorged themselves, their translucent bellies turning red and swelling so large that they struggled to flit away. Their eggs were later transferred to plastic trays of warm water.
Finally, after a tense two weeks in 1997, they began emerging from their pupae as Jasinskiene watched. Within minutes, she was knocking excitedly on James’ office door. The mosquitoes, she reported, had red eyes. After 10 years, James had made a giant leap toward creating the world’s first “good” mosquito--one that could be altered in the interest of mankind.
For nearly a generation, the genetic engineering at James’ lab and a few others around the world has been perhaps the best new hope for eradicating mosquito-borne diseases. When research to create a vaccine for malaria failed in the 1980s, it became the last in a long line of disappointments. Geneticists picked up the baton and, finally, they are drawing close.
Over the next few years, descendants of James’ mosquitoes almost certainly will be engineered to be utterly incapable of transmitting malaria, West Nile fever, dengue and other mosquito-borne diseases. Those mosquitoes might then be employed to genetically alter their evil cousins in the wild through interbreeding. If that happens, mankind may finally defeat an insect that has killed countless millions of people throughout history, thwarted scientists for more than a century and recently begun threatening Americans with new scourges.
Yet as scientists draw tantalizingly close, their obstacles have also taken sharper focus. The mosquito and the diseases it bears have a remarkable ability to develop resistance to human intervention. What’s more, in the years since geneticists embarked on this endeavor, many people have developed a profound reluctance to release genetically altered life forms into the environment. In a paradox only a mad scientist could appreciate, at the very moment that genetic research is poised for a breakthrough, doubts about the wisdom of their methods are growing. And it’s now possible that a miracle mosquito will be created but never released to work its magic.
To fathom the stakes in the race to make a savior mosquito, it helps to understand both the creature itself and the breadth of the world’s trouble with it. The female mosquito--only females drink blood--is a perfect agent for spreading infection in humans. Consider the last mosquito that dined on you. Equipped to sense the heat of your body and the carbon dioxide emitted every time you exhale, she was drawn directly to that patch of your skin not covered by clothing. She settled on your arm, or leg, or neck, and folded her glassy wings against her soft brown body. She walked so lightly on her six spindly legs that if you were absorbed in anything--a soccer game, picnic conversation--you didn’t sense her. She used the razor-sharp tip of her proboscis like an electric carving knife to slice you open. Twin tubes slithered toward a vein. While one tube tapped your blood, the other pumped in saliva, a slippery juice that encouraged the blood flow and may have also been loaded with a virus or parasite. You notice the attack only when your immune system produces a welt. By this time, this littlest of vampires is long gone.
In all of history, no walking or flying creature has delivered more death to more human beings that the lowly mosquito. Diseases carried by mosquitoes felled armies that attacked ancient Rome, made the interior of Africa inaccessible to European armies and periodically turned cities in 19th century America into ghost towns. During World War II, Gen. Douglas MacArthur estimated that, at one point, two-thirds of his troops in the Pacific had malaria symptoms.
Mosquito-borne diseases were driven out of the developed world by window screens, air conditioning, pesticides and huge drainage projects that eliminated breeding areas. Those techniques are still used to control the pests. “It’s usually a matter of nuisance control,” James says. “When you go to Disneyland, you won’t want to be the attraction for some mosquito that wants to bite you.”
For most of the 20th century, Americans enjoyed life without much fear of mosquito-borne diseases. But the recent arrival in the United States of the West Nile virus, which causes symptoms ranging from flu-like to paralysis or death and could spread throughout much of North America, has reminded us of the mosquito’s potential. However, West Nile, with its low fatality rate, is a tiny problem compared with the big three mosquito-borne illnesses: malaria, dengue and yellow fever. Worldwide, these diseases strike roughly half a billion people annually, killing an estimated 1 million. What’s more, the economic impact of mosquito-borne disease may be greater than HIV/AIDS. Business and industries won’t invest in regions where these pathogens thrive, nor will tourists visit. Thousands of communities in Africa and Asia have been isolated by disease for generations.
As long as the mosquito problem was confined to the Southern Hemisphere, it was easy for people in the industrial north to ignore. But since the fall of Communism and the opening of borders, malaria has made a comeback in Central and Eastern Europe, where 62,000 cases were reported in 1998, the last year for which figures are available. Western Europe saw more than 12,000 cases in 1997, four times the number in 1981.
Closer to home, mosquito-borne dengue, also known as breakbone fever, has roared back to life in Central America after almost disappearing from the Western Hemisphere. Outbreaks killed more than 100 people last year, and the virus has been found in mosquitoes on the U.S. side of the border with Mexico. Although dengue is the most immediate mosquito-borne threat, international flights and ships laden with imports can deliver new mosquitoes and diseases along with their freight and passengers.
These problems have led governments and private agencies to fund a revival of the mosquito science field. A year ago the London School of Hygiene and Tropical Medicine received a $40-million mosquito-research grant from the foundation created by software magnate Bill Gates. (This is part of a $125-million commitment the Gates foundation has made to fighting mosquitoes and their diseases.) In recent months, President Bush included mosquito research in a new $200-million federal fund for global health research, and an anonymous donor gave $100 million for malaria and mosquito science to be conducted at Johns Hopkins University. The $800,000 annual budget at James’ lab is small, but the research being done there is big. The creation of a savior mosquito is the most novel strategy being pursued, and James’ team is leading a race that involves about half a dozen groups worldwide. Several other labs are investigating so-called “smart pesticides” that could target only mosquito larvae while leaving the rest of nature untouched. Vaccines are being developed against West Nile, and, after a long hiatus, work is resuming on vaccines for malaria.
Ironically, the spectacular failure of a previous malaria vaccine programNconducted in the 1970s and 1980sNwas partly responsible for the slow progress in the field. For years, the main figures in the vaccine project reported that success was just around the corner. But after more than a decade, and many millions of dollars, they could not produce a safe, effective serum against a parasite that goes through multiple developmental stages in the human body.
This failure was the last in a series of disturbing surprises in the long-running battle between man and mosquito, which began in the late 19th century, when a British scientist named Ronald Ross discovered that the insects carried malaria. (Until then, the widely held explanation for malaria was, as the word suggests, “mal,” or “bad” air.) Once the mosquito connection was confirmed, sanitation and science produced great advances. The Panama Canal was made possible by the crews that eliminated breeding grounds for mosquitoes that bore yellow fever. Anti-malaria drugs and insecticides saved tens of millions of lives.
But it turns out that mosquitoes can adapt against even the most effective pesticides, and malaria parasites will develop resistance to our best drugs. An American-financed campaign to wipe out malaria in the 1960s ultimately collapsed because mosquitos developed resistance to DDT, the pesticide that was used. DDT would later be banned for environmental hazards associated with its widespread use. And drugs lost their effectiveness among troops in the Vietnam War.
It was against this background that the idea of fighting mosquitoes with mosquitoes was advanced as the first new concept in years. Andrea Crisanti of Imperial College of Science, Technology and Medicine in London called the pursuit of a transgenic mosquito “our Holy Grail.” A new generation of mosquito scientists began discussing the possibility of altering an insect so that even if it acquired viruses or parasites, it would not pass them on. At the time, labs were routinely changing the genes of fruit flies, mice and other animals. How difficult could it be to make good mosquitoes?
“We had been locked into using the same tools for years and they weren’t working,” recalls Frank Collins of the University of Notre Dame, an early backer of mosquito genomics. “Then a younger group came along that had the interest and energy to try this technique.” Funding flowed from the National Institutes of Health, the Wellcome Trust of Great Britain and World Health Organization. And then, for a long time, nothing happened.
Tall, lean and loose-limbed, 49-year-old anthony James walks down the hallway toward his lab. He pulls at the sealed door and steps into the tropics. “I would say we tried 80, maybe 90, experiments, each involving thousands of eggs. A lot of our grad students came and went without seeing anything happen. No success. It got so our weekly meetings were about nothing but failure. It was horrible.”
The main trouble was in the bit of DNA scientists used to break into the mosquito genome and deposit the new eye color gene. They chose an element called P, used routinely to alter fruit flies. But try as they did, they couldn’t make P work. Finally, in the mid-1990s, new transposable elements, named Hermes, mariner, Minos and piggyBac, were developed at labs around the world. James used Hermes, named for the Greek messenger god, to make his red-eyes.
Once James proved that mosquitoes could be altered, he and scientists in other labs began looking for genes that would stop the transmission of viruses and parasites a mosquito might ingest from an infected person. In the case of malaria, the parasite has evolved through the millenniums to use the mosquito’s body as a kind of safe harbor, where it transforms itself, and multiplies. Eventually it migrates to the insect’s salivary glands and waits to be delivered the next time the mosquito feeds.
Since mosquitoes will always be with us, and always biting, it seemed logical to try to disrupt the relationship between the insect and the pathogens that use it for transportation. James took a big step in this direction last year, engineering a gene that can produce an antibody in the mosquito that attacks malaria parasites. He then inserted it in adult mosquitoes using a virus. This method didn’t change the genes of the insect, but it did allow James to test the malaria-killing antibodies. The test was successful. It reduced the number of parasites in the insect’s salivary glands by 99.9%.
During the past year, genetic material that would fight the dengue virus was identified and installed in mosquitoes through the same virus method. (James teamed with a lab at Colorado State University.) These also worked. Other genes are being identified by researchers around the world. One prominent project at Michigan State University uses new genetic material to coax mosquitoes to produce their own antimicrobial compound--a naturally occurring substance called defensin--to kill pathogens when they are acquired.
James is certain he and his competitors “have all the pieces now.” He says this as he returns to his small office. “Sitting here, it may seem esoteric to talk about creating these mosquitoes and dealing with diseases like malaria and dengue. But if this works, and we get the mosquito we want, we could solve a problem that has plagued people forever, and still does today.”
Provided mankind wants to take that step.
If geneticists succeed in the lab, their work will enter an arena vastly unlike the controlled environment of the insectary. They will press for release of their custom-built critters, and at that moment will encounter a challenge of a different order. Remember the uproar that greeted genetically altered vegetables in Europe--the British tabloids called them “Frankenfood”? You can imagine what might happen if some government decides to loose millions of man-made insects.
Mosquito makers and their supporters will face daunting and alarming questions: Could the man-made mosquitoes mutate in some unexpected way? Might their matings with wild insects produce even more dangerous disease carriers? Is it possible that the genetic engineers would produce, in the end, not a savior but a super-pest?
“What about the people--most likely villagers in Africa or Asia--who live where these mosquitoes would be released?” asks Dr. Andrew Spielman of the Harvard School of Public Health. “Would they be asked for their informed consent? How could we be sure they really understand the risk? What about those who don’t want to participate? Would they be allowed to use insecticides or bed nets to protect themselves from biting? And what’s to prevent the mosquitoes you release from flying off?”
Spielman, 71, has a half-century of experience fighting blood-sucking arthropods everywhere, from Cuba to Sri Lanka. “It’s impossible to nurture a pest,” he says. “People won’t stand for it.” By way of example, he recalls the commotion in the 1970s over a plan to release sterile male mosquitoes in rural India, in hopes that the local mosquito population would be reduced. Trucks loaded with thousands of mosquitoes arrived in the countryside. But the project could not go forward because a few local politicians spread rumors that it was a sinister American experiment to study the use of mosquitoes and yellow fever virus for biological warfare against India.
Beyond that, Spielman and others quarrel over the amount being spent to engineer mosquitoes. The money could be better used to build economies in poor communities so that breeding areas are eliminated and houses are fitted with window screens. In a recent issue of the journal Science, medical entomologist Chris Curtis of the London School of Hygiene and Tropical Medicine, one of the oldest mosquito labs in the world, pleaded with donors to “keep in mind that every million dollars given to a few molecular biologists” trying to engineer mosquitoes could pay instead for lifesaving drugs and insecticides.
Spielman, in whose Harvard department James once worked, also sees three barriers between success in altering mosquitoes and actually beating back disease. First there’s the problem of fitness. Genetic engineering may produce a mosquito weaker than its wild counterparts and unable to survive in nature. Second is the issue of genetic consistency. Over time, man-made animals can lose the traits installed in the lab. Third is the complexity of the mosquito population. In certain places, malaria is transmitted by as many as seven different populations that rarely interbreed. How could one good mosquito convert all of those?
When it comes to funding medicine and science, a natural tension exists between the needs of today and tomorrow. It would cost billions of dollars per year to give the appropriate treatment to every human being who contracts a mosquito-borne disease. Even then, the pathogens have an uncanny ability to develop resistance and overcome our best medicines.
On the other hand, research into better mosquito-fighting technologies has not produced anything approaching a panacea. Then the genetic engineers came forward. Their ideas seemed fantastic at first, but they came when the rest of the field had exhausted its options. Although he respects the contributions they made, Collins wonders if the resistance voiced by old-timers is due to a lack of imagination.
He suggests that some veterans of the mosquito war witnessed the failures of DDT and malaria vaccines and became discouraged. Younger scientists, who didn’t endure those failures, are better-equipped to imagine the possibilities of genetic research. “When you are trying to make a substantial change in the way a problem is addressed, you have to be able to say, ‘Yeah, that could work,’ ” Collins says. “Some people can’t say that.”
However, significant progress has been made toward mapping the genomes of both mosquitoes and malaria. These projects could be completed this year. At the same time, the development of new transposable elements continues.
All this science promises many new tools for bioengineers. In a few short years they may be able to manipulate mosquitoes in the same, easy way that fruit flies are altered every day in hundreds of labs. Some geneticists have suggested that mosquitoes could be altered to feed on animals and reject human blood. It may also be possible to kill off huge populations of mosquitoes with a gene that makes males sterile. This strategy has already been used to halt both Mediterranean fruit flies and the screw-worm fly, which attacked cattle in the southern United States.
Once the mosquito gene-splicing becomes reliable, the options are mind-boggling. If a region has seven species that carry malaria, it may be rather simple to make seven new but friendly versions that will replace the bad ones. If experimenters want to confine mosquitoes to a small area, they can use genes from those species known to stick close to home. Monitors can watch for the kind of deterioration of valuable genetic traits that Spielman predicts, and order up reinforcements if necessary.
The astounding variety of mosquito species--there are more than 2,500--presents technologists with a smorgasbord of traits that could be used to advantage. One, nicknamed the satyr effect, would be especially useful. In mosquito species with this trait, males aggressively mate with every female they encounter. A new species could quickly invade an area and wipe out rivals.
When all of the genetic options are taken into account, you can imagine a day when anti-malaria, anti-dengue, or anti-West Nile mosquitoes could be custom-made for any environment. Indeed, the biggest single obstacle may not be scientific but, as Spielman indicates, social. It is possible that people just won’t accept the introduction of a pest, even one that is good for them.
Although opponents could claim to be on nature’s side, an argument can be made that science, including genetic engineering, is part of the human animal’s own adaptation to its environment. “When you think about what viruses and bacteria and parasites do to us, you see that we are in constant conflict with our environment,” says Alexander Reikhel, a competitor of James whose Michigan State University group is engineering mosquitoes. “Scientific research is our defense mechanism. Our enemies adapt. So must we.”
James is thrilled by the science he is doing, and driven by the competition to make the first, and then the best, new mosquito. “Hey, I’m never going to pitch for the Dodgers,” he says. “But we’re seeing things here in this lab that no one on earth has ever seen before. That’s pretty great.”
Like Spielman, James has visited villages where a quarter of the children born each year are killed by malaria, and everyone else is weakened by the parasites teeming in their blood. But his experience has led him to a different conclusion. “I think Andy might be wrong. The people in those places have seen enough sickness and death that if you told them releasing a new mosquito might help, they might try anything, if you ask.”
James could get his answer in a relatively short time. His work on the hardy A’des aegypti that resists the dengue virus should be finished in about a year. Since this is the species responsible for spreading dengue viruses in Latin America, a field test would be proposed immediately to determine whether the new mosquito could thrive in the wild. To improve its chances of gaining public acceptance, James says, the U.S. agency overseeing the mosquito-makers would suggest confining the experiment to an island. Perhaps an uninhabited one would be best.
