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In this elicitation,  students conduct a role-play to examine how a vector transmits a disease.

In a continuation of this, Lesson 3-2, teams of students research West Nile virus and six mosquito-control techniques. 

1. Before the activity, begin with a few review questions:

• Review the following terms:
• Host: an organism on or in which another organism lives
• Vector: an organism, such as a mosquito or tick, that does not cause disease itself but which spreads infection by carrying disease causing microbes, such as viruses, bacteria, and Plasmodia, from one host to another. Vector is the Latin word for a “bearer.”
• Ask if anyone has gotten sick due to an insect bite. Insect-borne diseases include Lyme disease, West Nile virus, Rocky Mountain spotted fever, encephalitis, and malaria. Explain that for these diseases, the disease-carrying insects are the vectors for the disease-causing microbes.
• Ask if students can guess what organism is the most dangerous vector on Earth. The mosquito is the most dangerous vector on Earth.
• Review how and why mosquitoes bite people. Female mosquitoes use blood to help their eggs develop. They insert a sharp proboscis into the skin and inject an anticoagulant to help the blood flow easily. This exchange of fluids is how disease-causing microbes enter a host.

      2.  Watch the video "Deadly Messengers" (~55 minutes). This program recounts the stories of the    

           heroic scientists and health workers who battled against the mosquito.

      3.  Have a brief post-video discussion with a few questions:

• What steps could one take to avoid being bitten by mosquitos?   
• Wear long-sleeved clothing and long trousers
• Apply mosquito repellent containing DEET on exposed skin and thin clothing
• Use a mosquito net when sleeping (preferably one treated with insecticides)
• Discourage mosquitos from entering an area by using window screens, spraying insecticides or burning insecticide-impregnated tablets and coils.
• Eliminate standing water anywhere around your property, ex. birdbaths and gutters.
• Why are diseases that are transmitted from human to human not considered vector-borne?  Some diseases are transmitted directly from one person to another without requiring a vector as an intermediary. Thus, while the common cold, flu, and measles are infectious diseases, they are not considered vector-borne diseases because can be transmitted directly from person to person.

       4.  Vector Transmission Role Play Procedure:  Use the following role-play to explore how a vector transmits disease-causing microbes and to brainstorm ways to halt the spread of the vector borne disease. 

• Distribute a small paper cup or paper towel to each student.
• Designate one student as the vector and give him or her a bowl of popped popcorn, which represents a disease-causing microbe.
• Give the vector 30 seconds to put popcorn into as many empty cups or paper towels as possible. Infecting a student requires at least five kernels because not every mosquito carries disease-causing microbes and increased exposure increases the risk of getting sick.
• After the vector has finished the round, count how many students became infected.
• Identify the components of the disease cycle. 
•  The popcorn is the disease-causing microbe.
• The person carrying the popcorn is the vector.
• The new host is a student with at least five pieces of popcorn.
• Brainstorm ways to prevent popcorn from getting into the individual cups.
• Answers may include: covering the empty cups, which represents using insect repellent or nets to prevent being bitten by an infected insect; preventing the vector from delivering the popcorn, which represents applying an insecticide or eliminating breeding areas; and emptying the small cups of popcorn, which represents curing an ill person.

 DO NOT tell the students "THE ANSWER".  Tell students that with the elicitation questions we are looking for all the different ways, models and theories that might explain the situation. Let students know that during the following lessons we will sort through all these ideas, but we need to have lots of ideas so that we can eliminate some.

This Lesson Provided by PBS.org

• Deadly Messengers Video (via YouTube)
• Deadly Messengers Video (via PBS.org- may need plugins) 
• Bowl of popped popcorn
• Paper cup or paper towel for each student