BUFFALO, N.Y. -- 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
"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
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
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
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
"Malaria epidemics usually occur in June and July," he
explained. "If you look at the whole year, you won't see the
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
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