|Like A Surgeons Knife|
"If people weren't poor we wouldnt have malaria," said Roberts. One only needs to look at a global map of malaria outbreaks to get an accurate depiction of where the standard of living is low. Outbreaks blanket Central Africa, India, Pakistan, and Southeast Asia. In the Western Hemisphere, a large epidemic exists over the Brazilian rain forest. From there the disease winds its way up through Central America and into Mexico, stopping a few hundred miles south of the United States, which was also covered with the disease not more than sixty years ago. (World Health Organization, 1998)
The reason malaria infects impoverished areas, Roberts asserted, has little to do with hygiene, the water supply or a bad diet. Rather, it has to do with the lack of protection impoverished people have against mosquitoes. The Anopheles mosquito breeds in standing water, is most active at night and usually bites people as they rest in their homes. In poorer areas of the world, drainage systems are usually substandard, so these types of mosquitoes breed in droves. Once the larvae reach the adult stage, villagers have no way to keep them out of their houses. Most houses in these areas do not have air conditioners or screens, and some just consist of a thatched roof and a dirt floor. These people cannot afford bug repellents or nets. As they eat or sleep, the mosquitoes come and go as they wish.
"But Malaria is a preventable disease," Roberts said, "The reason it is not prevented is money, and a commitment on the part of the governments to protect the people." In the past, people have suppressed malaria by spraying DDT (dichloro-diphenyl-trichloro-ethane) or other less effective, repellents on houses. The sprays kill or keep the mosquitoes out of the houses at night when they bite. However, implementing such a program requires the chemicals and hundreds of workers to distribute them; and spraying houses once is not a permanent solution. To really put a damper on malaria, houses must be sprayed annually, said Roberts. Some governments are too poor to sustain such a program with no outside help. Other governments simply do not care. Generally, the more unstable a government is, the worse malaria epidemics become.
Roberts and his team began their project fifteen years ago to help those governments with good intentions, but a lack of funds. They based their research on the idea that vector-borne diseases have definable determinants that can be mapped. As most diseases spread, they generally follow the economic, political, racial and even sexual boundaries of our society. Tuberculosis, for instance, infects areas where people have poor hygiene and medical facilities. Hepatitis C reaches new victims through blood transfusions, sex and shared needles. Those who live at the edge of a forest are at no greater risk than those who live near a swamp or desert. The local terrain and climate make little difference.
Vector diseases, on the other hand, are transmitted by insects and animals,
which live, feed and reproduce in specific environments and have unique ways of
coming into contact with people. While socioeconomic factors can still play a
role, the risk of getting infected ultimately comes down to a persons
exposure to the disease-carrying creatures environment. Scientists can map
the risk factors for a vector-borne disease as they would map a flood plain or a
Poor nations are affected disproportionately by malaria. People who can not afford air conditioners and tightly sealed houses are susceptible to mosquito bites, and those who cant afford expensive anti-malaria drugs are potential reservoirs of the disease. (Maps from Roll Back Malaria, World Health Organization)
Using modern technologies such as remote sensing satellites, Roberts team planned to identify the environments in which mosquitoes breed and those homes where occupants are most prone to contracting malaria. "The way we wanted to use these technologies was like a surgeons knife. We wanted to go target houses according to their risk," he said. With such a system, nations could then cut the disease off at the source simply by spraying those houses and areas that have the greatest risk of infection. This strategy could avoid the monetary and environmental costs of spraying every village in the country.
For the past fifteen years, since the project began, the scientists have conducted most of their research in Belize with the help of NASA grants and the full support of the Belizian government. At the center of their research has been an effort to understand the patterns of past malaria outbreaks. The Belizeans set up a national malaria database containing the names and addresses of every reported malaria case in Belize. Roberts team then assisted the government in looking for trends in the database.
They found that the risk of malaria in each house is pretty much constant over time. Certain houses, due to their location, their construction and a number of other factors, have a disproportionate number of malaria outbreaks. In fact, more than fifty percent of malaria cases in most villages occur in less than fifteen percent of the houses. Knowing this, Roberts team developed a system to categorize these houses in terms of the number of malaria outbreaks they've had. By spraying these houses alone, Roberts explained, Belize can rid itself of most of its problem. "If you have a house or an area that is producing a large number of malaria cases, that house becomes the source of infection for many other people in the neighborhood," he said.
|The larvae of Anopheles vestitipennis, a potentially important vector of malaria, occur in cattail marsh habitats. Houses, like those visible in the background, are frequently constructed in close proximity to these mosquito habitats. (Photograph courtesy Dr. Donald Roberts, Uniformed Health Services)|