The Case of Yellow Fever

1. Build and Verify.Figure 1. Model of Yellow Fever with values shown at the peak of the epidemic.Build the model in Figure 1. Initialize the model with 19,900 vulnerable people and 100incubating people. The mosquitoes may be initialized with 417,000 safe mosquitos and 83,000 newmosquitos. All other stocks may be set to zero. Simulate the model for 280 days, and you should see theresults in Figure 2. The simulation begins with 100 people in the incubation stage. The epidemic reachesits peak by the 140th day with around 450 sick people. The peak death rate is around 18 people/day.(Kalgraf does not comment on the magnitude of the peak death rate, but it is approximately the same asthe reports from Veracruz.) The simulation shows the peak of the epidemic in the 140th day. Figure 1focuses on the peak day by providing a "snap shot" in what appears to be an equilibrium diagram. Butyou can see that system is not in equilibrium because there are over 8,000 people who remain vulnerableto the disease.The mosquito stocks, on the other hand, are close to dynamic equilibrium. There are 81,259mosquitoes in the "new" category. Each of these mosquitoes bites 0.2 humans per day, for a total of over16,000 bites per day. But only 4.2% of these bites draw blood from a contagious human, so they becomedangerous flow is 686 mosquitoes/day.Andrew Ford BWeb for Modeling the Environment 2