Spacecraft May Give Early Heads-Up on Infection Trends

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Satellite technology could give public health officials advance warning of disease outbreaks likely to occur as a result of global climate change, researchers said.

Preliminary efforts have already produced models that predict spikes in diseases ranging from cholera to hantavirus on the basis of remote sensing data, according to Timothy Ford of the University of New England in Biddeford, Maine, and colleagues.

Writing in the September issue of the CDC's Emerging Infectious Diseases, Ford and colleagues -- including Rita Colwell, former director of the National Science Foundation -- said novel patterns of infectious disease are likely to accompany the regional temperature and hydrological trends that add up to climate change.

"If climatologic data can be used to predict future disease outbreaks, public health interventions can be mobilized in a more timely and proactive manner," they said.

"Successful predictive modeling of disease and the establishment of early warning systems have reached a critical junction in development. As we improve our understanding of the biology and ecology of the pathogen, vectors, and hosts, our ability to accurately link environmental variables, particularly those related to climate change, will improve."

They added, "We cannot stress too strongly our belief that a strong global satellite program is essential for future disease prediction."

They noted that the 2001 report from the Intergovernmental Panel on Climate Change predicted that the average number of people exposed annually to storm surges -- which frequently carry Salmonella, Vibrio, Cryptosporidium, and hepatitis pathogens -- will probably rise from 50 million people worldwide today to 250 million in the 2080s.

Altered frequencies and tracks of storm systems are also likely to mean inland flooding of areas that aren't exposed to it now. Ford and colleagues said areas of increasing drought may also be at risk for novel disease outbreaks. On example is meningococcal meningitis, which is endemic in sub-Saharan Africa during dry conditions and disappears at the start of the rainy season.

Climate Change May Bring on Disease

New patterns of vector-born diseases are another expected consequence of climate change.

Ford and colleagues pointed to several projects that have shown preliminary success in relating satellite data to disease:

Distribution of five out of six Anopheles gambiae mosquito species, vectors for the malaria parasite in Africa, has been modeled from remote sensing data on land use and climate parameters.

Remote sensing data in the southwestern U.S. correlated significantly with subsequent outbreaks of rodent-borne hantavirus pulmonary syndrome.

Eight of nine spikes in Bangladeshi cholera rates from 1998 to 2002 were successfully modeled on the basis of satellite data on sea surface height and temperature and chlorophyll A levels.

Ford and colleagues cautioned that the predictive power of these models is still weak. For example, 2005 Landsat imagery showing higher-than-normal rainfall in northern New Mexico and southern Colorado led health officials to warn of increased risk of hantavirus in those areas. The hypothesis was that rain promotes plant growth in the region, leading to a population boom in deer mice who carry the virus.

Cases indeed spiked in New Mexico during early 2006. But no increase occurred in Colorado, which actually saw fewer hantavirus infections than the previous year.

On the other hand, Ford and colleagues said, "these results are not necessarily a failure of prediction." Instead, they suggested that people may have heeded the health warnings prompted by the prediction, avoiding deer mice habitats and hence the virus.

Public health officials would dearly love to be able to predict influenza outbreaks, and the seasonality of the disease has raised hopes that environmental data will somehow be used in predictive models, the researchers said. Unfortunately, scientists still don't understand the specific factors underlying the flu's seasonal nature.

Scientists Strive to Predict Outbreaks

If science can isolate the environmental drivers of seasonal diseases like influenza, better prediction will likely become a reality, they suggested.

"As we improve our understanding of the biology and ecology of the pathogen, vectors, and hosts, our ability to accurately link environmental variables, particularly those related to climate change, will improve," Ford and colleagues wrote. "What has become clear over the past few years is that satellite imaging can play a critical role in disease prediction and, therefore, inform our response to future outbreaks."