Evidence Shows Warming Climate Will Worsen Malaria Epidemic
Researchers have debated for more than two decades the likely impacts, if any, of global warming on the worldwide incidence of malaria, a mosquito-borne disease that infects more than 300 million people each year.
Now, University of Michigan ecologists and their colleagues are reporting the first hard evidence that malaria does—as had long been predicted—creep to higher elevations during warmer years and back down to lower altitudes when temperatures cool.
The study, based on an analysis of records from highland regions of Ethiopia and Colombia, suggests that future climate warming will result in a significant increase in malaria cases in densely populated regions of Africa and South America, unless disease monitoring and control efforts are boosted and sustained.
"We saw an upward expansion of malaria cases to higher altitudes in warmer years, which is a clear signal of a response by highland malaria to changes in climate," said University of Michigan theoretical ecologist Mercedes Pascual, senior author of a paper scheduled for online publication in Science.
"This is indisputable evidence of a climate effect," said Pascual. "The main implication is that with warmer temperatures, we expect to see a higher number of people exposed to the risk of malaria in tropical highland areas like these."
More than 20 years ago, malaria was identified as a disease expected to be especially sensitive to climate change, because both the Plasmodium parasites that cause it and the Anopheles mosquitoes that spread it thrive as temperatures warm.
Some early studies concluded that climate change would lead to a big increase in malaria cases as the disease expanded its range into higher elevations, but some of the assumptions behind those predictions were later criticized. More recently, some researchers have argued that improved socioeconomic conditions and more aggressive mosquito-control efforts will likely exert a far greater influence over the extent and intensity of malaria worldwide than climatic factors.
What's been missing in this debate has been an analysis of regional records with sufficient resolution to determine how the spatial distribution of malaria cases has changed in response to year-to-year temperature variations, especially in countries of East Africa and South America with densely populated highlands that have historically provided havens from the disease.
Pascual and her colleagues looked for evidence of a changing spatial distribution of malaria with varying temperature in the highlands of Ethiopia and Colombia. They examined malaria case records from the Antioquia region of western Colombia from 1990 to 2005 and from the Debre Zeit area of central Ethiopia from 1993 to 2005.
By focusing solely on the altitudinal response to year-to-year temperature changes, they were able to exclude other variables that can influence malaria case numbers, such as mosquito-control programs, resistance to anti-malarial drugs and fluctuations in rainfall amounts.
They found that the median altitude of malaria cases shifted to higher elevations in warmer years and back to lower elevations in cooler years. The relatively simple analysis yielded a clear, unambiguous signal that can only be explained by temperature changes, they said.
"Our latest research suggests that with progressive global warming, malaria will creep up the mountains and spread to new high-altitude areas," said co-author Menno Bouma, honorary senior clinical lecturer at the London School of Hygiene & Tropical Medicine. “And because these populations lack protective immunity, they will be particularly vulnerable to severe morbidity and mortality."
In the Debre Zeit region of Ethiopia, at an elevation range of between 5,280 feet and 7,920 feet, about 37 million people (roughly 43 percent of the country's population) live in rural areas at risk of higher malaria exposure under a warming climate.
In a previous study, the researchers estimated that a one degree Celsius temperature increase could result in an additional 3 million malaria cases annually in Ethiopia in the under-15 population, unless control efforts are strengthened.
"Our findings here underscore the size of the problem and emphasize the need for sustained intervention efforts in these regions, especially in Africa," Pascual said.
In addition to Pascual and Bouma, the authors of the Science paper are A.S. Siraj of the University of Denver, M. Santos-Vega of the U of M Department of Ecology and Evolutionary Biology, D. Yadeta of the Oromia Regional Health Bureau in Addis Ababa, Ethiopia and D. Ruiz Carrascal of Columbia University.
Visit EcoWatch’s CLIMATE CHANGE page for more related news on this topic.
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Association Versus Intervention Studies<p>Many studies on the vitamin are association or observational studies. "By definition, these studies cannot prove the causal relationship, but only point to mere correlations," said Fassnacht. The physician tries to illustrate this with an example:</p><p>"Imagine two groups of 80-year-olds. One group is spry, active and does sports. If you compare them with another group living in nursing homes, the difference in vitamin D levels will be dramatic. Life expectancy would also be extremely different."</p><p>But to try to explain the difference in fitness by vitamin D status alone is far too simplistic. "Vitamin D levels are a good measure of how sick someone is. But not more," says Fassnacht. </p><p>According to Fassnacht, none of the intervention studies carried out to date -- that specifically examined the effect of vitamin D on various diseases -- has been able to confirm the previous association and laboratory studies or the presumed positive effect of vitamin D.</p>
Further Research Is Needed<p>"If a coronavirus infection is suspected, it is therefore absolutely necessary to check the vitamin D status and quickly correct any possible deficit," said the recommendation of the paper published by the University of Hohenheim.</p><p>"Studies are underway to see whether vitamin D helps in COVID-19 infection, but I personally do not believe that this is really the case," says endocrinologist Fassnacht. Nevertheless, he says it is of course useful to carry out these studies.<br></p><p>"I don't want to rule out that there are actually subgroups of people who benefit from an additional vitamin D dose," he says. After all, this has been proven to be the case with a severe deficit.</p><p>In view of the study situation, Fassnacht does not think much of preventive, nationwide vitamin D substitutes. "My belief that the vitamin helps somewhere is very low. But, of course, I can be wrong."</p>
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