Reading the Disease Forecast in the Weather Report
WHY YOU SHOULD CARE
Because an early warning system makes sense for more than just extreme weather. What if it could notify us that an epidemic were about to strike?
Since last December, an Ebola outbreak has spread from villages in the forests of southeastern Guinea to Liberia and beyond — with no signs of waning. Across the two countries, Ebola has killed 932 people, while the number of confirmed cases hovers at 1,711. The devastating disease spreads through blood, saliva and other bodily fluids. Intense weakness and fever give way to diarrhea, vomiting, and internal and external bleeding.
For outbreaks like this one, epidemiologists take a surveillance approach, waiting for people to fall sick before distributing medication and other resources. The problem is that it takes time to gather these resources, meaning that help arrives only after the epidemic peaks. “The idea is to be able to get ahead of the curve and deploy those resources in a targeted way,” says John Balbus, M.D., senior adviser of public health at the National Institute of Environmental Health Sciences.
It takes time to gather these resources, and help arrives only after the epidemic peaks.
Countries could save countless lives and vastly lower health care costs if they could prepare for infectious disease outbreaks ahead of time. Now, it may be possible for them to do just that. A recent wave of research has emerged to develop early warning systems to predict outbreaks of Ebola and other infectious diseases — using weather forecasts.
Climate change might make it more crucial than ever to develop early warning systems, according to the latest International Panel on Climate Change (IPCC) report, released last month. Warmer temperatures create friendly habitats for disease-causing microbes, not to mention the mosquitoes and other animals that carry them. And climate change can also cause extreme weather patterns, creating ideal conditions for disease transmission, Balbus says.
Ebola, meningitis, malaria, dengue fever…
For example, NASA researchers have linked past Ebola outbreaks with a particularly dry period followed by a sudden, heavy wet season. In rainy weather, bats that carry the Ebola virus reproduce more, infecting their mates, while primates — also carriers — roam more widely. An extremely rainy season would consequently result in the buildup of a large “reservoir” of Ebola virus. Examining satellite data for this Ebola-triggering weather pattern might allow public health workers to predict future outbreaks.
Balbus adds that researchers have been aware of a close relationship between weather patterns and health for years. But “we’ve gotten away from it in the 20th century as we moved from living in much closer connection to our ecosystems to living indoors, driving cars. Climate change is reawakening us to a very important connection to our environment… and our own health.”
Of course, extreme weather conditions, such as floods, can directly threaten human health and safety, resulting in death, crop failures and famine. But climate change’s link to infectious disease is harder to detect, since other factors, such as poor access to health care, can also play a role. And since many early warning systems are still being developed or have just recently launched, there isn’t much data on their effectiveness. Climate change still has an influence on infectious disease, but “the link… is more complicated,” Balbus says.
“As we obtain more years of data on the impacts of climate change on health and disease, the connection will continue to grow,” said Jennifer Vanos, an assistant professor in the atmospheric science group at Texas Tech University.
By monitoring satellite data, ’we hope to forecast epidemics one to two months ahead of time.’
Other researchers have also devised early warning systems, primarily in developing counties, which have limited resources to respond to outbreaks. Scientists at the Fraunhofer Institute of Optronics and other institutions are working on a computer system called EO2HEAVEN to predict cholera outbreaks in Uganda. They’ve used satellite data on rainfall and other environmental variables, as well as information on cholera patients from hospitals and doctors, including their symptoms and location. Each patient appears as a red dot on a digital map. By correlating the dots with environmental data, scientists aim to track how fast and far an outbreak is spreading.
Meanwhile, Pietro Ceccato, a research scientist at the International Research Institute for Climate and Society at Columbia University, is integrating satellite data with Google Earth and NASA’s SERVIR (a regional visualization and monitoring system) to predict meningitis outbreaks in Africa’s Sahel region, nicknamed “the meningitis belt.”
Meningitis-causing bacteria seem to favor dry, dusty conditions. Some researchers think dust particles can irritate a person’s throat and increase his or her vulnerability to infection. And dust storms force people to stay indoors, where they might transmit meningitis more easily to one another. So Ceccato’s team is monitoring satellite maps of dust levels in the air, which refresh every three hours. Eventually, his team hopes to use climate information to determine vulnerability for a variety of diseases. “We hope to forecast epidemics one to two months ahead of time,” he said.
Some forecasting systems have already shown promise. In 2006, the National Malaria Control Programme developed a system in Botswana based on population vulnerability, health surveillance and rainfall (since malaria risk has been observed to surge immediately after an intense rainy season). It can forecast malaria outbreaks up to five months before they peak, allowing health organizations to distribute mosquito nets to at-risk populations in advance.
Early warnings are useful only when heeded.
And in 2013, Umeå University researcher Yien Ling Hii designed a model that forecasts dengue outbreaks about four months in advance, based on her findings that dengue risk rose three to four months after a period of hot weather and heavy rainfall. High temperatures can accelerate the development of mosquitoes that carry the disease, while rain produces puddles and other breeding sites.
But early warnings are useful only when heeded. “Some early warning systems are simply ignored,” says Virginia Burkett, chief scientist for global change at the USGS and a lead author on the new IPCC report. “They’re not a panacea.”
Other researchers agree. “Early warning systems and other adaptations can be part of a broader part of addressing climate change,” adds Chris Field, co-chair of the latest IPCC report and director of the Carnegie Institution for Science’s Department of Global Ecology. Otherwise, the resulting environmental damage and health risks might surpass our ability to adapt to them.
“Early warning systems don’t address all climate-related problems,” Field says. “But it’s a start.” For developing countries with scarce resources to counteract full-on epidemics, it may be a good one.
Updated August 8, 2014.