West Nile Virus

This activity uses the SIRfull Stella model. We will investigate the effects of the following assumptions:

• AveSpringRain - Is June wetter or drier than an average year? If AveSpringRain is 1/2, only half as much rain falls. If it is 2, twice as much rain falls.
• AveSummerRain - Are July, August and September wetter or drier than an average year?
• AveSpringTemp - Is June cooler or warmer than an average year?
• AveSummerTemp - Are July, August and September cooler or warmer than an average year?
• VirulenceinB, BdaystoRecover and InitialSickBirds are the same as before. BdaytoDie is how long the birds that eventually die are infectious.

Base Case: Open the model. If you need to clear the graph, use the Dynamite icon at the bottom of the graph. Set the sliders at:

• AveSpringRain = 1
• AveSummerRain = 1
• AveSpringTemp = 1
• AveSummerTemp = 1
• VirulenceinB = 0.1
• BdaystoRecover = 4
• BdaytoDie = 14
• InitialSIckBirds = 0

Run the model.

The rainfall curve tells you which days it rains.

The curves now have lots of small increases and decreases, which seem to be tied to when it rains. When it rains, there is more standing water so more mosquitoes are born. Just before it rains, it is warmer, so more mosquitoes are born then too. So just before and after it rains, there are more susceptible mosquitoes. In the middle of the week, susceptible mosquitoes have been dying and becoming infected, so the number of susceptible mosquitoes goes down.

In the middle of the summer (days 45 to 90), do you see a pattern in the curve representing the number of mosquitoes incubating the virus?

In the middle of the summer, what is the pattern for infectious mosquitoes?

Weather Pattern for 1999: Use the Dynamite icon at the bottom of the graph to clear the graph. Set the sliders at:

• AveSpringRain = 2
• AveSummerRain = 0.5
• AveSpringTemp = 0.8
• AveSummerTemp = 1.2
• VirulenceinB = 0.1
• BdaystoRecover = 4
• BdaytoDie = 14
• InitialSIckBirds = 0

Run the model.

How is the infection pattern in the last month (Days 90-120) different?

Higher Virulence: Use the Dynamite icon at the bottom of the graph to clear the graph. Set the sliders at:

• AveSpringRain = 1
• AveSummerRain = 1
• AveSpringTemp = 1
• AveSummerTemp = 1
• VirulenceinB = 0.4
• BdaystoRecover = 4
• BdaytoDie = 14
• InitialSIckBirds = 0

Run the model.

How is the infection pattern in the last month (Days 90-120) different? Why?

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