Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Assign 10% of the students (3 students) to play the role of infected mosquitos. Give them a red dry-erase marker.
2. Assign 10% of the students (3 students) to play the role of uninfected mosquitos. Give them a blue dry-erase marker.
3. Assign 30% of the students (9 students) to play the role of robins.
4. Assign 20% of the students (6 students) to play the role of humans.
5. Assign 10% of the students (3 students) to play the role of scrub jays.
6. Assign 10% of the students (3 students) to play the role of crows.
7. Assign 10% of the students (3 students) to play the role of horses.

Safety Precautions

This laboratory activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Disposal

Wipe check marks off of the cards with a damp cloth or paper towel. All materials may be saved for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students
• Take the time to further analyze the results of this lab other than the data required to complete the chart of the worksheet. For example, count how many of each type of bird survived or died to exhibit differences in immunity to the virus.

Teacher Tips

• Have students research other diseases such as Dengue Fever and Yellow Fever to determine similarities and differences between the transmission of the virus.

Answers to Prelab Questions

1. What organism serves as the vector of West Nile Virus?

   Mosquitos.

2. What does it mean to be a dead-end host of West Nile Virus? Name at least one species that would meet this criteria.

   A dead end host means that the species can get the virus but they traditionally don’t transmit it to others. Humans and horses are considered dead-end hosts of WNV.

Sample Data

Answers to Questions

1. Which type of animals tends to have the greatest fatalities associated with West Nile Virus?

   Birds.

2. Why do mosquitos make an ideal vector for the West Nile Virus?

   Mosquitos are an ideal vector because they are able to be infected by the virus but it does not give them any adverse symptoms. They are also ideal because they feed on animals that are able to replicate the virus.

3. How does the number of infected and uninfected mosquitos change throughout the game? What does this mean in regards to how an infection spreads?

   The number of infected mosquitos increases throughout the game. Once they are infected they are always infected, it does not go away. The more mosquitos that become infected the faster the virus will spread.

4. In this game if a mosquito bites an infected bird it will become infected. In nature, the probability that a mosquito will become infected depends on the type of bird it bites. For example, 40% of mosquitos that bite an infected scrub jay will obtain the virus and only 17% of mosquitos that bite an infected robin will obtain the virus. Discuss one possible reason this might occur.

   As discussed in the Background section, different species of birds are more or less infectious than others. One birds’ immune system may allow the virus to replicate easily. Conversely, another may be less infectious in that the virus has a harder time replicating, therefore having a lower transmission rate to future mosquitos.

References

From Birds to People: The West Nile Virus Story. Howard Hughes Medical Institute. http://www.hhmi.org/biointeractive/birdspeople-west-nile-virus-story (Accessed August 2014).

The West Nile Virus. Illinois Department of Public Health. http://www.idph.state.il.us/envhealth/wnv.htm (Accessed August 2014).

West Nile Virus Transmission Cycle. The Mayo Clinic. http://www.mayoclinic.org/diseases-conditions/west-nile-virus/multimedia/west-nile-virus-transmission-cycle/img-20006044 (Accessed August 2014).

Introduction

West Nile Virus was first found in the United States in New York City during the summer of 1999. Since then, cases have been documented across the continental United States. It is important to study disease transmission such as WNV because it can help scientists determine how infectious diseases originate, how they spread from one species to another and why cases spike and practically disappear depending on the time of the year.

Concepts

• Vectors
• Viruses
• Disease transmission

Background

Vector-borne diseases are illnesses such as viruses, bacteria and parasites that living creatures carry and pass on to other living creatures. The living creatures that carry and pass on the disease are known as vectors. Vectors are typically insects or arachnids such as mosquitos, fleas, lice, mites or ticks. For example, mosquitoes carry the infectious agents that cause West Nile Virus. Other vector-borne diseases include Lyme disease, Dengue fever, Avian influenza and rabies. Having a vector, such as a mosquito, increases the virus’s ability to spread.

Vectors usually become infected by a disease agent while feeding on an infected vertebrate. In the case of West Nile, female mosquitos usually attain the virus by feeding from an infected bird. The virus eventually enters the entire mosquito’s body, including its salivary glands. The female mosquito is then capable of passing the virus along to humans and other animals when collecting its next “blood meal.” Mosquitos are mostly unaffected by the virus, whereas the virus is fatal to some species of birds when the virus often dies. Figure 1 illustrates how the virus is transmitted among species.

Different species of mosquitos have different preferred “blood meal” prey. Birds are a favorite host. Some hosts are more infectious than others. For example, crows and blue jays are much more infectious than robins. Species that are highly infectious allow the virus to replicate more easily inside their body. Therefore, if an uninfected mosquito bites a highly infectious species they are more likely to contract the virus and pass it on.

Humans are much less infectious than birds. Therefore, it is difficult for the virus to replicate inside them as a host. Humans and other animals such as horses are known as dead-end hosts. Although the virus can infect humans and sometimes cause illness, it will not spread. If an uninfected mosquito bites an infected human the virus will not be transmitted to the mosquito. This is because the virus is not able to replicate enough inside a human for a mosquito to aquire the virus. Once humans obtain the virus, the only way it could be further transmitted to someone else is if they gave blood for a transfusion or donated an organ.

Humans have a wide variety of reactions to contracting the virus. More than 80% of those who obtain West Nile from a mosquito will have no symptoms at all. Mild cases of West Nile infections may cause a slight fever or headache. More severe infections are marked by a rapid onset of a high fever with head and body aches, disorientation, tremors, convulsions and, in the most severe cases, paralysis or death. Usually symptoms occur from 3 to 14 days after the bite of an infected mosquito. Individuals at the highest risk for serious illness are those 50 years of age or older.

Experiment Overview

It is important to understand how disease vectors aid to spread a particular disease quickly. By studying West Nile researchers can gain a greater understanding of other similarly transferred viruses such as Dengue Fever. In this game students will play a vector (mosquito) or a host organism to simulate how West Nile Virus is transferred from one organism to another and how it effects overall populations.

Materials

Prelab Questions

1. What organism serves as the vector of West Nile Virus?
2. What does it mean to be a dead-end host of West Nile Virus? Name at least one species that would meet this criteria.

Safety Precautions

This laboratory activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Procedure

Round 1

1. Arrange the host organisms (robins, scrub jays, crows, humans, horses) to be standing in a line or dispersed throughout the classroom.
2. Mosquitos are to randomly “bite” as many hosts as possible in a 60-second time span. When an uninfected mosquito bites a host they check the host card in circle 1 with their blue dry-erase marker. Similarly, an infected mosquito will check the host card with a red marker. Note: Each host can only be bitten once per round.
3. After a mosquito bites a host it can move on to bite the next host.
4. Repeat step 3 as many times as possible in the 60-second time period allowed.
5. At the end of the round, count the number of infected and uninfected mosquitos and hosts. Record in the West Nile Virus Transmission Worksheet.

Round 2

6. Mosquitos randomly bite as many hosts as possible marking circle 2 with the appropriate marker. Reminder: Each host can only be bitten once per round.
7. If an uninfected mosquito bites an infected bird host (their card was previously marked with red in circle 1) the mosquito is now infected and must exchange their blue marker for a red marker and mark all subsequent hosts of the round with red marker.
8. If an uninfected mosquito bites an infected human or horse (their card was previously marked with red in circle 1) it does not become infected and will keep their blue marker.
9. If an infected host dies at the end of round 2 the player must sit down and may no longer be bitten in later rounds.
10. Count the number of infected and uninfected mosquitos and hosts at the end of round 2. Record in the West Nile Virus Transmission Worksheet.

Round 3

11. Mosquitos randomly bite as many hosts as possible in 60 seconds, placing a check in the host card in circle 3. Reminder: Mosquitos cannot bite dead hosts.
12. As in round 2, if an uninfected mosquito bites an infected bird host that has a red check in circle 1 or 2 it becomes infected and must exchange a blue marker for a red marker.
13. As in round 2, if an uninfected mosquito bites an infected human or horse, the mosquito will not become infected.
14. At the end of round 3, count the number of infected and uninfected mosquitos and hosts.

Student Worksheet PDF

11260_Student1.pdf