Predicting Malaria Outbreaks Using NASA Satellites

Narration: Joy Ng


In the Amazon Rainforest, few animals are as dangerous to humans as mosquitoes that transmit malaria. In the Western Hemisphere, 90 percent of all malaria cases occur in the Amazon, but it’s not spread evenly across the tropical region. While malaria has decreased in the Brazilian Amazon, the disease has been steadily increasing in the Peruvian Amazon. In the past 5 years, Peru has had on average the second highest rate in the South American continent. Despite having interventions such as bed nets and indoor sprays, challenges still lie in identifying where to send resources before malaria outbreaks occur and spread quickly. Now scientists are attempting to tackle this challenge using NASA satellites. Our project in the Amazon is trying to understand the way malaria is transmitted in a tropical environment. We know that malaria risk is associated with certain environmental conditions that we can detect from satellite. To understand what environmental conditions to look for, it helps to know how malaria spreads in the Amazon. Malaria is caused by a parasite called Plasmodium and it’s transmitted to humans when mosquitoes carrying the parasite feed on your blood. There are roughly 40 species of malaria-transmitting mosquitoes worldwide, but in the Amazon the Anopheles darlingi species is most responsible for spreading malaria. The key to this study is predicting where the darlingi mosquito breeding sites are with NASA satellites. The project is using a model called the Land Data Assimilation System, or LDAS, and this gets input from NASA satellites that provide information on precipitation, temperature, soil moisture, and land cover. This informs scientists where mosquito breeding sites are likely to form. Mosquitoes need rainfall to form their breeding sites – puddles and ephemeral ponds. Rainfall also influences soil moisture. That will be important for vegetation. It will also change the humidity conditions near the surface where mosquitoes are breeding and living. Rainfall also eventually makes its way into the river and a lot of river discharge will mean that there’s lots of breeding sites along the banks for mosquitoes. There are strong patterns of malaria throughout the year, but these patterns aren’t consistent. As well as changes from season to season, global effects such as El Nino and climate change can disrupt where mosquitoes breed. Another factor that NASA satellites can detect is changes in land. The conversion of forest to non-forest is the most important change that we worry about for malaria control and the detection of hot spots. In Peru, land is cleared for activities such as agriculture, logging, and mining. And studies have found that cleared land in this region increases the number of malaria-transmitting mosquitoes. Changes in the land doesn’t just influence where mosquitoes are, it also influences where humans are and this is a key component in this study. One thing that we’ve learnt in this project is just how important it is to consider human movement when thinking about malaria risk. People work on land that is used for agriculture, logging, and mining so that increases the amount of human traffic to that area. Where people meet malarial mosquitoes that’s where you get high risk of a transmission. Figuring out where people are getting infected forms the crux of predicting malaria. Peru currently measures how many malaria cases are being detected in health posts. But this isn’t always where true malaria outbreaks are occurring. People are not necessarily being diagnosed where they were infected with malaria. They could be getting infected where they are working, which could be 100 miles away. To incorporate this factor, the study is combining the LDAS data with models that give estimates about where people are traveling based on studies of seasonal employment. The study will predict where malaria outbreaks will occur 12 weeks ahead of time and help the country send resources to specific regions efficiently. While the project is focused on malaria, scientists say it can adapt to other diseases such as Zika and Leishmania. Precipitation and other environmental conditions are key factors in how diseases spread and with NASA satellites scientists are better understanding how diseases are interacting with a changing planet.