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Man-Made Changes Are Linked To Malaria Transmission

Guiyan Yan, Ph.D., assistant professor of biological sciences and an ecologist at the University at Buffalo, has received a $3 million grant from the National Institutes of Health to determine how man-made environmental changes affect the transmission of malaria in Africa.

The first-ever study of its kind, the project will be used to develop methods of predicting malaria epidemics throughout Africa and to identify novel cost-effective malaria control strategies that can be used readily in Africa.

Malaria has long been a scourge -- particularly of children -- in the Caribbean, Southeast Asia, India and nearly all of sub-Saharan Africa. Each year, it kills between 1.5 million and 3 million people around the world and 95 percent of the deaths occur in infants and young children.

The mysterious re-emergence of the disease in the highlands of East Africa after a six-decade hiatus has baffled researchers since the first new cases were reported in 1988. Since then, malaria, which has caused thousands of deaths in a region that had been free of it, has become one of the area's two biggest infectious-disease killers. AIDS is the other.

"What we really want to achieve is to develop methods for predicting malaria outbreaks and to identify appropriate land-use policies that promote agricultural productivity and reduce infectious disease transmission," said Yan.

Yan conducts research in Kenya, where he studies mosquito population ecology and genetics, and in an "insectary" at UB, where he studies the molecular genetics of mosquito resistance to malaria parasite development.

With the NIH grant, Yan, along with David Mark, Ph.D., professor of geography at UB, and colleagues from the Kenya Medical Research Institute, will employ a broad range of multidisciplinary techniques, including geographic information system/remote sensing technologies, molecular biology and ecological models to understand why malaria has re-emerged in this region.

"Our hypothesis is that the re-emergence of malaria in the highlands is related to changes in land use; global climate changes also may play an important role," explained Yan.

One-third of Kenya's population of 27 million lives in high-altitude areas, or highlands, mostly because these areas are cooler and more suitable for farming. But the rapid habitation of the highlands in Kenya and in other African nations has come with fundamental changes in land use that have, the scientists say, created more fertile breeding grounds for the anopheline mosquitoes, the insect that transmits malaria to humans.

What makes the re-emergence of the disease in this region even more problematic is that people who live in the highlands generally lack immunity against malaria and so are even more vulnerable to the disease than those who live in areas where it traditionally has been found.

Currently, Yan said, the World Health Organization (WHO) is reporting that the use of mosquito nets sprayed with insecticide that are draped across beds at night has reduced deaths from malaria by 30 percent.

"This is the most effective weapon for combating malaria so far," said Yan. "However, in many African regions, the mosquitoes that transmit malaria parasites have developed resistance to insecticides."

He added that anti-malarial drugs developed 40 years ago also are becoming less effective. In most areas of Africa, he said, the malaria parasites have developed resistance to chloroquine, the most widely used treatment in Africa. When an epidemic sweeps through an area, it can kill hundreds or even thousands of people.

"The key to malaria control is prevention," said Yan, "and knowing when and where there will be an outbreak will help malaria prevention tremendously. Fewer lives will be lost if local residents and governments can be prepared early to combat malaria."

The project is the first to model the transmission of malaria using a spatial epidemiological modeling approach.

"This approach will tell not only whether there may be a malaria outbreak in an area, which a traditional epidemiological model can do, but it also will predict in which particular villages it may occur," said Yan.

Such predictions will be based on several variables, he explained, including human population distribution and land-use changes; the distribution of suitable mosquito larval habitats and adult habitats based on land-use, topography and rainfall, and distribution of malaria parasites.

"The eventual outcome will be a malaria forecasting system that will allow each nation's Ministry of Health to identify areas that are at high risk for outbreaks," he said.

According to Yan, a diverse range of land-use factors may be involved in malaria's re-emergence. These could include an increase in mosquito breeding habitats. For example, he said, irrigation creates many such habitats, as do animal footprints resulting from increased cattle grazing. Deforestation leads to more sunlight and higher water temperatures, which, in turn, may accelerate larval development.

"Our main objective is to develop an early warning system for malaria based on a thorough understanding of malaria epidemiology and information on land-use patterns and climate," said Yan.

General methodologies developed in the study also may be applicable to other so-called vector-borne diseases, including the West Nile virus and dengue fever, he said. - By Ellen Goldbaum

[Contact: Ellen Goldbaum]

31-Aug-2001

 

 

 

 

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