Seasonal fluctuations in a region's climate, rather than consistently high annual temperatures or levels of rainfall, play an important role in causing malaria epidemics in the African highlands, a new research paper by University at Buffalo biologists reports.
The paper, published online this week in Proceedings of the National Academy of Sciences, is the first to demonstrate a strong correlation between climate variability and the increase in malaria epidemics that have struck the African highlands since the late 1980s.
"Our data show that climate variability plays a major role in initiating malaria epidemics in the East African highlands," said Guiyun Yan, Ph.D., associate professor of biological sciences in the UB College of Arts and Sciences and senior author on the paper.
Under normal climatic conditions, Yan explained, malaria is rare in the highlands because of the region's cool weather. The mysterious re-emergence of epidemic malaria since the late 1980s in the East African highlands after a six-decade hiatus has baffled researchers.
Because individuals in these highlands lack the immunity that people have in regions where malaria transmission occurs year-round, their mortality rate is far higher.
In the PNAS paper, the researchers describe a statistical model they developed on the relationship between climate variability and the number of malaria outpatients between the 1970s and 1990s in seven areas in the highlands of Kenya, Ethiopia and Uganda.
They found that while average annual temperatures in these regions had not changed, there was significantly increased variability within the year in temperature and rainfall and that the number of cases of malaria strongly increased during the years with high climatic variability.
According to the paper, the model explained 65-81 percent of the variation from the mean in the number of malaria outpatients at the seven sites during the years included in the study.
"We found that since 1989, there have been significantly more highs and lows in temperature and rainfall in these regions," said Yan.
At the same time, they found that there were strong synergistic effects between temperature and rainfall on malaria cases.
"The use of either temperature or rainfall alone is not sensitive enough to detect anomalies in the climate that would signal a malaria epidemic," said Yan.
The UB research provides insight into the debate over whether or not changes in the climate -- specifically, global warming -- have contributed to the alarming increase in frequent malaria epidemics in this region, where previously the disease was rare.
Unlike recent papers that have defined global warming in the form of average annual temperatures, the UB research focuses on increases in temperature and rainfall during the months when malaria transmission is most likely to occur.
"For a malaria epidemic to happen, you don't need warming all year round," said Yan. "You do need some warming and increased rainfall in some months in order for mosquitoes to breed."
According to Yan, average annual temperature data will not reveal climate change that is more pronounced in specific months.
"Malaria epidemics usually occur in June and July," he explained. "If you look at the whole year, you won't see the climate signal."
The research was funded by a National Institutes of Health grant to Yan, the first grant to focus on determining how climate and man-made environmental changes might affect the transmission of malaria in African highlands, which have undergone rapid human settlement in recent years.
The UB research will prove critical to the ultimate goal of that research: predicting and eventually preventing outbreaks of malaria using novel, cost-effective control strategies.
Co-authors on the paper are Guofa Zhou, Ph.D., and Noboru Minakawa, Ph.D., both senior research scientists in the UB Department of Biological Sciences, and Andrew K. Githeko, Ph.D., a senior scientist at the Centre for Vector Biology and Control Research, Kenya Medical Research Institute, where Yan conducts the collaborative research.
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