Climate Change Could Affect Malaria Patterns, Researchers Say
Climate change could affect malaria patterns by reducing disease prevalence in some regions while increasing it in others, researchers said last week during the annual meeting of the American Association for the Advancement of Science in Chicago, SciDev.Net reports (Irwin, SciDev.Net, 2/17). According to Scientific American, climate change could cause malaria to "migrate away from" lower latitudes and increase in regions where populations have not developed immunity to the disease (McGlashen, Scientific American, 2/16).
Matthew Thomas of Pennsylvania State University at the meeting said that global warming could create temperature fluctuations that would threaten the life cycle of the Plasmodium parasite, which could reduce the prevalence of malaria in certain regions. According to SciDev.Net, malaria parasites do not develop sufficiently fast in temperatures lower than 16 degrees Celsius and are killed by temperatures higher than 40 degrees Celsius. However, Thomas said the parasite requires a cooler temperature, lower than 31 or 32 degrees Celsius, during the first 12 hours after it enters a mosquito. Therefore, "[i]f climate change increases the frequency of days when the temperature quickly exceeds the threshold temperature, then entire cohorts of mosquitoes could fail to develop the parasite," Thomas said. According to SciDev.net, climate change also could lead to an increase in malaria prevalence in some cooler regions, if average temperatures increase from 15 degrees Celsius to 17 degrees Celsius, for example. In addition, temperatures might exceed these averages during a substantial part of the day, which would accelerate the development of malaria parasites. According to Thomas, current predictions about the effects of global warming on malaria trends could be wrong by as much as 50% to 100%.
According to SciDev.Net, recent, unpublished research by Mercedes Pascual of the University of Michigan-Ann Arbor supports Thomas' predictions. For Pascual's study, researchers examined malaria patterns in Kenya's western highlands and found that a small observed temperature increase of 0.5 degrees Celsius was associated with a four- to five-fold increase in malaria incidence. Pascual said that predictions about malaria prevalence made with current models "are below the observed number of cases" (SciDev.net, 2/17).
Although some scientists have argued that either climate change or parasite adaptations could lead to an increase in malaria prevalence, Pascual said the two factors work together, with rising temperatures spurring a faster development of malaria drug resistance. According to Pascual, although no research has demonstrated the dual role of climate change and drug resistance in increasing malaria transmission, this model makes theoretical sense. She explained that "warmer temperatures increase transmission, so you're going to increase the number of people you treat" for malaria. Furthermore, research has demonstrated that treating more malaria cases can lead to a higher incidence of drug resistance, Scientific American reports. Christopher Thomas of Aberystwyth University in the U.K. said that although researchers do not know the specifics of how climate change will affect malaria prevalence, some changes already are occurring. "The change isn't coming at the end of the century," he said, adding, "[I]t's happening right now" (Scientific American, 2/16).
