The Mundane Space Revolution and Disease Prevention From Orbit
By Richard A. Lovett
In classic science fiction, space probes are used to detect life signs, spot indicators of alien civilizations, or monitor other large-scale parameters of value to intrepid explorers of the future.
But in today’s real world, satellites are both more ubiquitous and more mundane. According to the Union of Concerned Scientists, there were 1,419 operational satellites orbiting the Earth in 2016, of which 40% were American, 10% Russian, and 13% Chinese. Some were military, but most perform duties ranging from communications and weather monitoring to making land-use observations so precise they can tell farmers which parts of their fields need irrigation or pesticides—allowing huge savings both in money and environmental side effects. Space-based sensing has become so ubiquitous that we take for granted Google Maps images so detailed we can even spot our own cars if they happened to be at home when the satellite passed overhead. I’m sixty-four. If someone had told me in college that all of this would happen in my lifetime, I wouldn’t have believed it. Now, as a running coach, I routinely use satellite images to measure racecourses and training routes to precisions better than a few tenths of a percent.
In science fiction, it’s easy to imagine how such remote-sensing abilities could produce dystopian consequences. If today’s commercial satellites can spot individual cars, will tomorrow’s be able to follow pedestrians? Will they let the “fashion police” comment on my apparel choices every time I venture outside? Forget what the military or the police might be able to do; are we headed for a world in which spy eyes from space can show everyone every detail of our lives?
But that’s not the focus of this article. Yes there are dystopian concerns, but there are also incredible benefits, many of which can only be described as jaw-droppingly . . . mundane. Jaw-dropping in how valuable they might be. Mundane, because their values will come in parts of our lives so ordinary we may be slow to realize the extent of the revolution.
Some of these mundanely revolutionary changes are ones we are already tapping into every time we use our smart phones to get an hour-by-hour weather forecast or pull up maps that show not just the addresses of our destinations, but images of all the nearby buildings. About the time I started working on this article, I went to a friend’s birthday party on a snowy day. She lived on a hill I feared would be too icy to drive, so I used my smartphone’s map application to search for potential places to park near the base. A few years ago, that would have been incomprehensible. Now, I simply did it as a matter of course.
And that’s merely a convenience. The remote-sensing revolution also has the potential to be life-saving, albeit in ways we will barely notice, even if our own lives are among those that are saved.
Let’s zoom in on one aspect of this: the use of satellite data to provide advance notice of disease outbreaks—including important diseases such as malaria, West Nile virus, and Zika virus.
Not that I picked these diseases at random. All are vector-borne illnesses, meaning they are transmitted by animals: mosquitos in the case of these three, although there are plenty of diseases with other animal vectors.
Predicting outbreaks of such diseases from space is possible because mosquitoes, ticks, etcetera, have breeding zones that can be determined very precisely by combining satellite-derived weather information with space-based images of vegetation, stream drainages, wetlands, and other factors known to be ideal for an explosion of disease-carrying pests. These breeding zones can then be compared to maps of where people live to determine where conditions are ripe for a disease outbreak.
Historically, maps of where people live have been compiled from census data. More recently, for regions where census data are limited, they can also be derived from space-based measures of “night lights” brightness: the amount of illumination produced by electric lights. But both of these are coarse measures. Today, the same satellite images that power my cell phone’s map application can do the same thing, far more precisely. “I can tell where every one of you live,” said Uriel Kitron, chair of the Department of Environmental Studies at Emory University, Atlanta, at the 2015 meeting of the American Association for the Advancement of Science, in San Jose, California. “I can map all of your houses. I can find where the mosquitoes that might bite you are breeding. I can find the birds [that might carry West Nile virus to infect the local mosquito population].”
In one pilot study, Kitron’s team looked at Chicago rainfall and temperature patterns and determined how they affected the spread of West Nile virus, a disease that generally causes mild flu-like symptoms, but in some people can cause life-threatening complications such as encephalitis or meningitis. What they found was that the disease risk varied widely, even in areas got the same basic weather conditions.
“We found a high heterogeneity even within a small neighborhood,” Kitron said. “You practically have to go to the block level. We mapped the types of trees, the houses, the temperature data [and] the rainfall data to identify the locations where people are at highest risk of contact with mosquitos that transmit the disease.” In other words, one street might be at risk of West Nile outbreaks, while a nearby one might be less so. If you’re a public-health department wanting to know where to spray for mosquitoes to get the biggest benefits with the lowest costs and lowest environmental side-effects, that’s exactly the type of data you want.
Kitron’s team was able to convert this into a computer model that could predict where West Nile disease was likely to strike about two weeks in advance (roughly the breeding and development cycle for many mosquitos). Ideally, he would like to be able to predict mosquito-hatching conditions even further in advance. “But two weeks’ warning is not bad,” he said.
In another study, his team examined schistosomiasis, a disease transmitted via freshwater snails carrying a parasitic worm that goes from the snails into the water and then becomes a blood fluke in humans who come into contact with contaminated water. “It’s a big problem in the tropics,” he said, noting that it’s especially prevalent among children. (The World Health Organization estimated in January 2017 that two hundred thousand people die of it each year, with two hundred million requiring treatment.)
Working in Kenya, his team mapped locations where disease-carrying snails were likely to be found, comparing them to remote-sensing data showing the locations of up to 90% of human homes. They also used satellite images to examine the terrain and determine the overall water-flow system, “which is essential to understanding how snails move from one place to another,” he said. “We created a risk map for the movement of snails,” he added, noting that part of the process involves using satellite data to track changes that might cause snails to migrate closer to human population centers when drought conditions cause more-remote habitats to dry up.
Putting it all together, he said, “We tried to relate where you lived, and where you might go swimming or do laundry, to the chance you may become infected.”
In theory, it might be possible to do all of that with ground-based instruments, but satellites have many advantages. To begin with, they can look at even the most remote locations, where on-the-ground monitoring reports might be slow to nonexistent. NASA’s Soil Moisture Active Passive (SMAP) observatory, for example (launched in January 2015), can measure the moisture in the top two inches of soil around the world every two to three days. Other satellites can map sea-surface temperatures, air temperatures, rainfall, vegetation changes, and flooding far more comprehensively and quickly than all but the best land-based monitoring systems. The same method, he adds, can be applied to tick-borne illnesses such as Lyme disease, which infects somewhere between thirty thousand and three hundred thousand people a year in the U.S. alone, according to U.S. Centers for Disease Control and Prevention estimates. “Soil moisture is good for ticks,” Kitron says.
Yet another example comes from Kenneth Linthicum, director of the U.S. Department of Agriculture’s Center for Medical, Agricultural and Veterinary Entomology, in Gainesville, Florida, who has applied similar techniques to Rift Valley fever.
Rift Valley fever is a mosquito-borne plague affecting livestock and humans in parts of East Africa (although it has also appeared in Saudi Arabia, Yemen, Egypt, and South Africa). Primarily a livestock disease, it can cost affected countries hundreds of millions of dollars in losses due to trade bans. But it can also spread to humans through contact with infected animal blood or other tissues, producing thousands of debilitating illnesses and, in severe cases, death. The disease tends to crop up in the aftermath of heavy rainfall and floods, which expand the habitat—and breeding opportunities—for disease-carrying mosquitoes.
Linthicum’s team has been able to predict Rift Valley fever outbreaks as much as several months in advance—far enough out, he says, that it’s possible to use vaccines to protect livestock (and their human handlers) from infection. Even if an outbreak is in a remote region where vaccines aren’t available, he says, it’s still possible to reduce the impact simply by warning people that the outbreak is coming, and telling them to quarantine sick animals and avoid contact with them.
Archie Clements of Australian National University in Canberra has been applying the same techniques to malaria outbreaks in Melanesia. “Once you identify a hotspot, you can provide information for a spray team to mobilize,” he says.
Not that all diseases are as easily addressed. A nasty mosquito-borne viral disease called chikungunya, for example (which causes fever, intense joint pain akin to dengue fever, and occasionally death), is a case in point. In the Horn of Africa it appears to be enhanced by drought conditions and high temperatures. Drought appears to drive mosquitos closer to the wetter habitats favored by people, while high temperatures increase the likelihood that any given mosquito will transmit the disease. But in Southeast Asia, Linthicum says, the prevalence of the disease is linked to increased rainfall. “It depends on the ecology and becomes pretty complicated when you look at different parts of the world,” he says.
Other diseases aren’t transmitted by animal vectors. Many are transmitted by person-to-person contact, which has little to do with conditions such as soil moisture, rainfall, or temperature. I.e., in these cases, we ourselves are the vector. That doesn’t mean, however, that it’s impossible to track their spread by remote sensing. After all, the movement of people is also subject to remote monitoring. “There have been several studies that have been able to get data from cell-phone companies and look at people’s movement to see how people move, where they move to, and the risk of disease,” Kitron said.
Which brings us back to the beginning of this article, where we were looking at the increasing ability of satellites to track everything we do. Forget the super-detailed space-based pictures; satellites can also be used to track our cell phones, cars, and any other GPS-equipped device enabled to broadcast its location. And if they do that, they can also be used to track the movements of anyone with whom we cross paths.
When I started work on this article, I was trying to find a parking space near the base of a snowy hill. When I was finishing, a few days later, my phone interrupted me with a weird tone and informed me of an AMBER alert for a nine-year-old girl who had been reported missing in a town nearly three hundred miles away. (She was later found with her mother, who had apparently violated a custodial agreement.)
Forget the question of whether an alert needed to be sent immediately to people 300 miles away. What the incident made me realize was what will soon be possible. A few years from now, your phone may buzz equally urgently as you’re walking through a mall. “A person approaching you has been exposed to influenza,” it might then inform you. “Veer right, and/or hold your breath.” Similar warnings might even be given about the person about to serve you lunch at a food counter or sitting next to you in a movie theater.
Far-fetched? Maybe. But the technology to be able to do this is fast approaching. The mundane revolution has barely begun.
Copyright © 2018 Richard A. Lovett