Viruses in the News: Ebola
Lesson 11 of 11
Objective: Students will explain how viruses spread by researching the Ebola epidemic in West Africa and its transmission to the rest of the world.
Ebola is in the news every evening and recently it has come a little close to home. There are confirmed cases in Nebraska and Texas and a suspected case in Kansas City. That has been very unnerving for my students. In this lesson, we explore how several common viruses spread throughout the human population by using an interactive from the New York Times. Then we prepare for our summative writing assessment by drafting an outline for a blog post. Once that blog post is completed, it will be posted to our class blog "Keep Calm and Science On." Here is an overview of what students will learn today.
Have students watch the following video from the BBC News, Ebola: What is It? We'll Explain it in 60 seconds.
Have student complete a graphic organizer using the 5Ws and 1 H in their lab notebook or use this current events summary sheet while they are watching the video. Next they should write a quick summary from their outline.
Ask several students to read their summaries. Next, in their lab notebooks, have students write several questions that people might have the spread of Ebola, etc. Students can also share what they may have read and seen on the news.
(Note: To see how I do this with my students, check out my teaching reflection.)
Ask students the following questions:
- Why do you think it is important to understand how a diseases is transmitted?
(Possible answers: To understand if the method of transmission is airborne, vector, or droplet; to prevent other people from getting the disease)
- How can knowing how a disease is transmitted be useful in helping treat victims of that disease?
(Possible answers: to know how to treat their symptoms, to know how to keep them from spreading the disease to others, to know how to develop a vaccine)
- What is an epidemic?
(Possible answer: a widespread occurrence of an infectious disease in a community at a particular time.)
- How can knowing how a disease is transmitted be useful in responding to an epidemic?
(Possible answer: It enables health care workers mean to prevent the spread by wearing protective clothing. It lets you know if a person with the disease needs to be in isolation so they do not spread the disease. It lets you know if surfaces need to be treated with certain chemicals to prevent the spread of the disease.)
Explain to students that they are going to look at an interactive from the Washington Post that compares how quickly Ebola spreads compared to other diseases like smallpox, measles, and SARS. Students will work in pairs and only look at two diseases: Ebola and one other additional disease. (Note: I assign the additional diseases to my students to make sure all diseases are sampled. The interactive runs different scenarios so one than one student pair can have the same diseases.)
One students will need to create an Excel sheet on their computer (or use the one provided) while the other student runs the simulation on their computer. The simulation should be paused every five days and data needs to be recorded using on the Excel sheet. Once 100 unvaccinated people contract the disease that part of the simulation stops. The entire simulation stops once 100 unvaccinated people have gotten Ebola.
Next have students graph the data to determine the shape of the viruses growth curve. Time should be placed on the x-axis and number of infected persons should be placed on the y-axis. Have students determine which of the two viruses was more contagious (virulent) and which of the two viruses was more deadly. (Note: The graph with the steepest slope will be the most contagious. The virus with the highest death rate would be the most deadly. Have students determine the death rate for the disease by taking the number of deaths and dividing by 100, then multiplying by 100%.)
Bring the class back together and have them rank the disease by how virulent they are and how deadly they are. Have students summarize what they found in their lab notebook.
(Note: Here are some sample data (Sample student data 1, Sample student data 2, Sample student data 3) and student graph. Here is a list of what my class determined from the scenario they were given. Because there are several scenarios, the data your class has may vary.)
Modeling Exponential Growth
Ask students to describe the graphs that were made by using the data from the interactive.
(Note: Most students will fit a curve that will equal an exponential function. They may not be able to describe their curve as an exponential function yet. However, by the end of this section, they should understand what an exponential function is.)
Students should thought about how a secret might be spread among a group of people. Consider the following scenario: one person knows a secret and tells another person. On each subsequent day, each person who knows the secret tells only one other person.
- How long will it take for 25 people to hear the secret?
- How about 50 people or 100 people?
- How long will it takes 1000 people to hear the secret?
- How about 10,000 or 100,000 people?
Give student time to make predictions in their lab notebooks. Then reveal to the students that the number of people who have heard the secrete doubles every day.
- Ask students why they think this is?
(Possible answer: Every person who knows the secret tells another person. On day 2, four people know the rumor. On day 3, eight people know the secret. On day 4, sixteen people know the secret.)
Sketch a graph of predicting the possible spread of the secret. (Note: it should look like an exponential growth curve.) Then ask student if this graph looks similar to the graphs that they generated from the interactive that they just completed. Students should find that the spread of disease can mathematically be modeled just like the secret spreading scenario as long as certain assumptions are made. The biggest assumption that was made in the first scenario was 100% transmission rate.
Have students consider the following questions:
- How would the graph appear, if the transmission rate is less than 100%?
(Answer: If the transmission rate is less than 100%, the graph will be less steep.)
- What types of disease appeared to have a transmission rate of less than 100%?
(Possible Answers: Diptheria, Whooping cough...)
- How would the graph appear, if the transmission rate is more than 100%?
(Answer: If the transmission rate is more than 100%, the graph will be more steep.)
- What types of disease appeared to have a transmission rate of greater than 100%?
(Possible Answer: Influenza)
Modeling Logistic Growth
Next, explain to students that a more realistic model that explains the spread of disease. Briefly explain the difference between a logistic curve and an exponential curve. Draw the two curves on the board and ask student to speculate what conditions in nature might cause the taper at the top of the logistic curve.
(Possible answer: In terms of a viral infection, there are no more people to infect. People have developed an immunity, either by getting the disease or being vaccinated. Therefore, non-infected people are protected from getting sick.)
Introduce the essential vocabulary herd immunity and briefly explain what it is. Have students place it in the vocabulary section of their lab notebook.
Modified from The Mathematics of Epidemics. New York Times Learning Blog. November, 5, 2014. http://learning.blogs.nytimes.com/2014/11/05/exponential-outbreaks-the-mathematics-of-epidemics/
Have students brainstorm several topics about which they would like to include in their blog post. Assign topics to individual students or student groups. Allow students to search for possible article that will help them with their posts. Also, have them check their lab notebooks for possible resources. Have individual students or student groups create an outline for the blog post in their lab notebook. At the end of the hour students should turn in their lab notebook for evaluation and approval. Once approved, students will draft a blog post and submit it for peer review and editing. Upon final approval, the post will appear in the class blog, Keep Calm and Science On.
Homework: Students will evaluate several safety protocols to determine how epidemiologists attempt to limit the spread of disease. For each safety protocol, students should complete a current event summary sheet to discuss the safety protocols that our government has in place to prevent infection. Use the following links for the homework assignment: