Computer Models- Scientists sometimes use a computer model to help them think about a problem. It's sort of like looking at the reflection in a mirror. You see just one simpler image, a model representation, of the real world when you look in the mirror. In the case of computer models, researchers use math to describe how things look to begin with and to write the rules for how the picture will change over time. The rules are based on what the scientists think controls changes in the real world, and then applied to an imagined, or hypothetical, system. The rules and the system combine to form the model and the model runs on the computer. The scientists look at the answers the model has given them and compare those answers with their observations of what has gone on in the real world. If the patterns look alike, then maybe the mathematical rules the researchers used in the model can also be used as tools for studying the real world problem.

The Malaria Model- In our model, we use colors to let you know what is going on. And we made a series of movies for the Web site that shows the output from the model. The top square of the movie frame shows the spread of the disease. The whole square is filled with people. People who haven't been bitten yet are green, so the whole square starts out that way. (If you have been lucky enough to get vaccinated, you are dark green. This only shows up in one case and movie.)

Infection comes in two stages: yellow is for people who have been bitten and are incubating the parasite; red represents infected people who can spread the disease when they are bitten by a mosquito. People recover from the disease after several months and return to green, but only if they haven't been bitten again.

The same colors are used in the graph in the middle which shows how many people are healthy, bitten, and sick as the model runs for five virtual years. Each column represents one month.

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The spread of the disease is affected by the environment -- mosquitoes like wet places. The environment (shown in the bottom square of the movie) starts out grey, or neutral. We added wetlands and rice paddies or fish ponds that show up as blue patches. They change from dark blue to light blue as the seasons change from wet to dry. In one model, they disappear when they get treated.

Green spots show up in the rainy season. These represent seasonal wet spots around settlements -- places like puddles, ruts, ditches, and even flower pots that hold standing water where mosquitoes can breed. Watch how the disease lingers in these spots.