Imagine if researchers could predict illness outbreaks months into the future. They'd know where to concentrate resources and treatment medications, even offer vaccinations if the disease was preventable in this way. The United States already tries to do this with the flu, making predictions of when and where it might hit, and how bad it is likely to be.
Now scientists researching the influence of climate on malaria outbreaks have found a way to predict them as far as four months in advance in one part of the world. Previous efforts using monsoon rainfall totals have only been able to predict outbreaks a month in advance.
This information could be used to "prepare to have more insecticide in regions in times when you need it [and] to have in place sufficient drugs to have treatment for the population in these regions," said Mercedes Pascual, a professor in the Department of Ecology and Evolutionary Biology at the University of Michigan and co-author of a paper on the research, published Sunday in the journal Nature Climate Change.
The researchers studied a part of northwest India that, because of its aridity, is on the edge of malaria distribution, meaning that some years it does not have outbreaks, but other years, largely due to temperature and rainfall variations, it does.
In a retrospective analysis, they found that times of lower sea temperatures in the tropical south Atlantic Ocean in early summer were 80 percent accurate in predicting an outbreak of malaria in this part of the world in the fall. This is because the lower sea temperatures lead to the annual monsoons dropping enough rain to support a malaria-carrying mosquito population.
"So we see higher malaria when we have cooler sea surface temperatures in the tropical south Atlantic," Pascual said. "In a sense, we have found an unexpected teleconnection."
A teleconnection is a connection between a climate anomaly in one place and a climate anomaly in another, faraway place. The most well-known example of this is how El Niño, in the Pacific Ocean, can affect things like rainfall and temperatures in far-off areas.
Studying the edges
As the climate warms, it is likely that malaria will increasingly reach into places where before factors like temperature or dryness kept it at bay. Pascual is studying these edges, which are often either a little too dry to consistently have malaria, or, because of their altitude, are a little too cold. She is also working in the East African highlands in countries like Kenya and Ethiopia and in South America.
Places on the edge of malaria are both more and less at risk, Pascual said. Because the disease isn't a constant, there's a bigger risk that, once infected, people succumb to the disease, because they have not developed immunity. On the other hand, it's better to be located in a place that only sometimes has malaria than a locale where it is widespread.
"For control efforts, it can be a sort of surprise factor, the fact that some years you have a few cases, other years you have many more; that can make control of the disease difficult," Pascual said.
Some places that have previously avoided malaria outbreaks because of their elevation or relative coldness, like Quito, Ecuador, a high-altitude city, could become more susceptible in a warming world, said Ben Cash, a climate scientist at the Center for Ocean-Land-Atmosphere Studies and lead author of the paper.
Early warning of an outbreak is key because it allows public health officials to prepare in advance and efficiently allocate medicines or insecticides, Pascual said. "Often the resources are limited, and distributing the resources in terms of treatment and vector control, where those are most needed, could be helpful."
Cash, who has conducted a number of studies looking at the influence of climate on disease, said the association they found, linking changes in sea surface temperature in the tropical south Atlantic with rainfall and disease incidence, was new, because most studies looking at the influence of ocean temperatures on rainfall focus on El Nino.
Pascual is traveling to India soon, where she has been talking with public health officials who might be able to use the research in their planning for outbreaks. In the future, she says, she and Cash hope to refine their model in a way that allows them to pinpoint where more resources to fight malaria are actually necessary.
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