Malaria vs. Mankind: Chemicals, Conservation And An Ancient Arms Race
Part of a series investigating the complex linkages between human, animal and environmental health: The Infection Loop.
One steamy evening in July 1976, George Poinar Jr. climbed into a hammock strung up between two trees in West Africa's Ivory Coast. He swiftly zipped himself inside the tent of canvas and mosquito netting to ensure that the buzzing swarms didn't follow. Nevertheless, he awoke the next morning to find his right arm covered in bites; a wrong turn in his sleep had left the arm pressed up against the netting.
"I must have fed 25 mosquitoes that night," says Poinar, now a paleo-entomologist at Oregon State University.
A week or so later, Poinar experienced a severe bout of fever and chills. He struggled to hold a cup of tea steady. "I really thought I would die and never make it home to the States to see my family again," he told The Huffington Post.
At least one of his blood-sucking visitors apparently carried malaria. With a double dose of the antimalarial drug he'd already been taking to prevent infection, Poinar recovered enough that summer to continue his infectious disease research with the World Health Organization.
He was one of the lucky ones. More than 2 percent of all worldwide deaths, around 800,000 per year, are attributable to the disease.
Humanity has long battled the malaria-transmitting Anopheles mosquito. In fact, as Poinar explains in a recent paper published in American Entomologist, mosquitoes trapped and preserved in amber suggest that malaria parasites were already hijacking the insect's insides to reproduce some 100 million years ago.
"My goodness, these are old," Poinar recalls thinking when he first made the discovery inside the rare Burmese fossils. "They give us insight into how co-evolution has led malaria to be very well adapted."
The malaria parasite, Plasmodium, has evolved over the last couple of decades to withstand not only the preventative chloroquine Poinar took in 1976 -- at which time Plasmodium had already built up enough resistance that he needed a double dose to fight off the infection -- but also newer drugs, as evidenced by the recent emergence of artemisinin resistance in western Cambodia. And the malaria-carrying mosquitoes, too, are increasingly unyielding to the insecticides used in sprays and bed nets.
"That's what makes it so hard to control," says Poinar.
Malaria's long list of victims includes popes and poets, emperors and explorers, infants and infantry. Recent studies even suggest the disease may have contributed to the death of King Tut and to the fall of the Roman Empire. Still today, malaria is a constant threat for more than three billion people and takes the lives of thousands of children every day, mostly in sub-Saharan Africa.
But public health officials are now declaring that humanity's parasitic nemesis may have finally met its match. "In this day and age, no one should be dying from a disease that is entirely preventable and treatable," Margaret Chan, Director-General of the World Health Organization, told attendees at the 2011 Malaria Forum, hosted by the Bill & Melinda Gates Foundation in Seattle this October. "This time we are staying one step ahead of malaria."
This echoes the overly optimistic pronouncement of the U.S. Surgeon General in 1969: "The war against diseases has been won." More than four decades later, infectious disease remains the number one killer of children worldwide.
Our disease-fighting weaponry has certainly improved in recent years, from the widespread distribution of insecticide-treated bed nets to hopeful progress towards a malaria vaccine. But Poinar and other experts suggest that getting ahead of the disease, let alone maintaining a lead, is far easier said than done. It doesn't help that the parasite leads such a complicated life both inside the mosquito and the human host. As Nathan Myhrvold, founder and CEO of Intellectual Ventures, explained at the forum, Plasmodium is unlike most other infectious organisms: "The damn thing has sex, so it evolves much faster."
When a female Anopheles mosquito draws blood from a person (or, in some cases, an animal) infected with malaria, male and female sex cells of the parasite head to the insect's gut where they fuse, sparking a complex reproduction process. Depending on the strain of the parasite, new generations can develop in about a month; the ability to exchange genetic material sexually maximizes the adaptive changes each time around.
James McCann, director ad interim of the Pardee Center for the Study of the Longer-Range Future at Boston University, warns that drugs and vaccines alone are not likely to win the arms race against such a fast and resilient foe. "We need to look at malaria as an ecology disease, as distinct from a disease of biomedicine," he tells HuffPost. "And we need to be clever and multidisciplinary in how we address it."
That might mean the help of economists, ecologists, social scientists and engineers. It might also mean thinking about malaria from the perspective of the parasite or mosquito. Like humans, Plasmodium and its winged carrier have basic needs, including food, water, sun and sex. How humans alter its access to these requirements -- by manipulating a landscape or the flow of a river, for example -- may help or hinder the spread of disease. And all of this may be influenced by the context of the place, including its social, political and economic conditions.
"New medical interventions, bed net programs, trials of a malaria vaccine -- these are all wonderful developments," Jonathan Patz, director of global environmental health at the University of Wisconsin, Madison, tells HuffPost. "But too often we ignore the root causal factors for why we even have malaria in a location."
Those underlying factors are still not completely clear. When Patz recently visited the Dalai Lama at his home in India, Patz described (among other ecological challenges) the difficulty in understanding why and how mosquitoes pick and choose different spaces. The Dalai Lama's response: "You should have just asked the mosquito."
Patz's current theories center around the problem of deforestation. Two to three percent of the world's forests are lost each year as trees make way for more people. Fewer trees, of course, means more open, sun-drenched land -- a welcome change for certain malaria mosquitoes. Several Anopheles species, including the most prevalent and deadly in Africa, seem to prefer to lay their eggs where the sun shines.
After accounting for the size of local human populations and other possible variables that influence mosquito abundance, Patz found a nearly 200-fold increase in malaria risk when he compared the most and least degraded rainforest sites in the Peruvian Amazon.
"Preserved forests provide many different benefits, from serving as a carbon dioxide sink for the problem of greenhouse gases to protecting biodiversity," he says. "Now, as our work is showing, it also has fairly direct benefits to public health."
The indirect benefits themselves may not be insignificant. Slight changes in temperature or precipitation patterns can alter the ability of both the cold-blooded mosquito and the parasite to survive and reproduce. At 64 degrees Fahrenheit, for example, malaria parasites reproduce too slowly to mature during the lifetime of a mosquito; but at 68 degrees, they can reproduce in plenty of time to get passed along by the flying syringe.
Destroying forests also puts at risk potential future medicines, including those that might someday help prevent or treat malaria (many antimalarials, past and present, derive from botanical sources).
One of the major efforts underway to save rainforests is the United Nation's Reducing Emissions from Deforestation and Forest Degradation (REDD) program, which offers financial incentives for developing countries to keep their trees standing. However, as Patz notes, only carbon dioxide emissions are currently considered when putting a value on an intact forest. If REDD could incorporate a broader range of benefits, the program might go even further to benefit both the environment and public health.
People inadvertently provide mosquitoes with moist breeding grounds through other means as well: by building new roads that change the flow of water run-off or by creating fish ponds to serve as a source of protein. "Unfortunately, the fish are probably not eating the larvae," says Patz, adding that particular mosquito-eating fish could be enlisted.
"Using environmental approaches where appropriate makes a lot of sense," says Dyann Wirth, chair of immunology and infectious diseases at the Harvard School of Public Health. "The challenge in Africa is that Anopheles mosquitoes can adapt quite readily. So changes you make may have unanticipated effects."
One telling example dates back to the 1950s: The WHO sprayed large amounts of DDT to counter a malaria outbreak in Borneo, successfully killing off malaria mosquitoes, as well as some pesky cockroaches. "Everything was wonderful," says Patz. But then thatched roofs began falling on peoples' heads. The pesticide, it turned out, had also killed off wasps that ate thatch-eating caterpillars. What's more, the pesticide moved up the food chain, poisoning lizards, which were then eaten by cats. And as cats died, rats flourished, spreading new diseases, including typhus. WHO responded by parachuting in more cats.
"We can't solve one problem in isolation without considering the interconnections," says Patz. "Otherwise, you may cause more harm than good."
SICKNESS vs. HUNGER
There are often trade-offs, too. Strategies to combat infectious diseases and address food insecurity, for instance, aren't always compatible.
When Boston University's McCann arrived in Burie, Ethiopia, in 2005, it was very different from what he remembered from his two-year stay in the 1970s. Back then, the area was malaria-free. "There were no mosquitoes," McCann recalls. "There was no reason to be awake at night from buggers buzzing around."
But sometime in the subsequent decades, mosquitoes moved in and brought malaria with them. McCann's former landlord and other townspeople shared horror stories of entire schools abandoned and of houses simply locked up because no one inside had survived.
McCann, an agricultural expert, noticed something else that had changed: widespread planting of a new variety of corn.
Lacking food security, Africans have embraced just about any opportunity to squeeze more sustenance from the earth. The new maize, which grows faster and more abundantly than traditional varieties, had "spread like wildfire," McCann says.
The locals call it "Silsa Sidist," or 66, short for BH660. While the varietal is a powerful example of agricultural technology's potential, McCann feared that the product may have a serious drawback: The plant sheds pollen at the same time that mosquitoes lay their eggs. And this particular pollen is perfect food for the larvae. As McCann puts it, the right temperature and right humidity come together to create the "perfect storm."
Curious to see if this explained the local surge in malaria, McCann worked with an Ethiopian malaria expert to study where farmers were growing the super corn and where people were getting malaria. They found 10 times the rate of malaria associated with the new corn as compared to other crops.
McCann shared their results with a local agriculture manager. "I just got this look of, 'Yes, you've convinced me,'" recalls McCann.
"And then he said, 'Don't tell anyone.'" Farmers weren't about to give up their prize crop.
Agriculture represents the largest driver of landscape change around the world, accounting for at least 40 percent of the global land surface. With strategic management of this land, McCann suggests that there need not be a choice between keeping communities fed and disease-free: Farmers could plant other lucrative crops, such as red peppers, in the most malaria-prone areas, while researchers could pursue a high-yield variety of maize that sheds its pollen earlier in the season.
Mark Wilson, a malaria expert at the University of Michigan, notes that since water is also a necessary component for breeding mosquitoes, farmers could plant the corn on a slight slope or cultivate it in a way that doesn't leave furrows for rain to fill.