Activity 2
Ebola and Measles on the Move: Tracking the Spread
Introduction
The purpose of the activity is to have students explore the role of human behavior in the spread of Ebola and measles.
While human behavior is a factor in diseases that are the result of contaminated food and water — humans fail to keep excrement out of their water supplies (cholera) and humans fail to practice sanitary procedures during food preparation (Salmonella infections) — these diseases can be stopped by regulating city and town water supplies and food preparation by companies.
Changing human habits requires education of the population about dangers of certain practices, some of which are steeped in personal beliefs, traditions, and long-standing habits.
While the biology and ecology of infectious agents plays an important role in determining their spread, the emphasis in this activity is primarily on human behavior. The biology and ecology of viruses as determinants of infectivity is explored in greater depth in the Module 3, Viruses Go "Viral".
Reading: Patient Zero
In this reading students explore the first big idea of epidemiology, identifying the index case or Patient Zero, the first recorded case of a disease in an outbreak or epidemic.
Identifying patient zero in an epidemic is critical. By knowing where the disease first occurred, scientists may be able to identify the source of infection and prevent future outbreaks.
- Who was patient zero in the Ebola epidemic and measles outbreak?
- How did he get infected and how did it spread from him?
Students specifically look at how the first Ebola and measles cases were identified.
Activity
In this activity students identify factors that influence the spread of Ebola and measles and suggest ways that could prevent or halt outbreaks and epidemics based on their findings. You may want students to then design an intervention or program to educate individuals about the dangers of a practice and that could help individuals change or eliminate that practice.
Materials
One copy of the Factors Chart (downloadable below) for each student or for each team if activity is done collaboratively.
On the digital version of the chart below, click "show factors" to see the factors influencing the spread of each disease highlighted in blue.
| Ebola | Measles |
|---|---|
| Animal reservoir | No animal reservoir |
| Transmission - direct contact with body fluids from infected individuals | Transmission - aerosol through inhalation of droplets from lungs of infected individuals |
| Not very contagious | Highly contagious |
| High fatality rate (50–90%) | Moderate fatality rate (1–30%) |
| Recently developed vaccine; highly effective but not widely available | Effective vaccine; widely available |
| Likely immunity after infection or vaccination | Definite immunity after infection or vaccination |
| Burial customs in a country have relatives touch the body of the deceased person | Burial customs vary |
| Global travel is highly common across many nations | Global travel is highly common across many nations |
| Access to healthcare limited in many affected countries | Access to healthcare varies in affected countries |
| Access to clean water limited in many affected countries | Access to clean water varies in affected countries |
| Wild animals used as food source in many affected countries | Wild animals may be used as food in affected countries |
| Mutations in the viral genome occur as the virus moves from person to person | Strains of the measles virus,can be identified by antibody assays of surface proteins |
Notes on the above chart:
- The existence of an animal reservoir makes it very difficult to eliminate an infectious disease. Measles with no animal reservoir could be eliminated if .90% of individuals were vaccinated. Eliminating the reservoir is probably not feasible
- Direct or close contact is involved in the spread of disease. If patients were isolated the spread could be limited or halted
- The infectivity of the virus is a factor. This factor will be discussed in greater depth in the Viruses Go “Viral” module
- It could be argued that the greater the fatality rate the lower the spread because patients die. However, this is probably not a major factor in Ebola or measles.
- Burial rituals are a definite factor in the spread of Ebola whereas are not a factor in measles. Altering burial rituals or have no contact with the body during burial would prevent infections.
- Global travel was definitely a factor in the spread of both Ebola and measles. Checking travelers for illness or stopping travel from countries with the disease perhaps could confine the spread.
- Access to healthcare meant many patients with Ebola remained in homes and were attended by families with no protective gear or practices so they became infected. At first signs of illness, patients could be admitted to a facility dedicated to Ebola patients. Such action could prevent the spread to family and caretakers
- The consumption or association with wild animals carrying Ebola was likely a factor in initiating the epidemic (see Patient Zero) but is probably not involved in the spread of the disease. Since measles has no animal reservoir it is definitely not involved.
- Changes in the virus have no known role to date but do allow epidemiologists to track the path of the epidemic as it spreads.
Procedure
-
Distribute Factors Chart to students. Inform them that, based on their understandings so far about Ebola and measles, they will identify factors involved in the spread of these infectious agents and factors they may make its elimination possible or difficult. You may want them to look at the Ebola and measles information found in the Epidemics timeline.
- Have students identify the factors they deem important in the spread and justify their decisions about why they think each factor is important. They should also consider how these factors could be altered or changed to prevent or halt an outbreak or epidemic. Students should be prepared to share their decisions and justifications.
- Have students share their decisions and reasoning in a whole class discussion and discuss ways that these factors might be eliminated or altered.
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You may want to facilitate a discussion regarding the challenges of changing certain behaviors. For example:
- Changing habits or traditions based in deeply held personal or religious beliefs
- Economic factors in poor countries
- Ethical concerns regarding enforced isolation of infected individuals or in barring travel from certain countries or in requiring vaccinations for every child.
- On January 14th, 2016, the World Health Organization announced the end of the Ebola epidemic in Liberia. Both Sierra Leone and Guinea, the two other countries that were devastated by the recent Ebola epidemic – had been pronounced Ebola-free earlier. These epidemics claimed 11,000 lives in these West African countries before the epidemic was halted. You may want to discuss this with your class and elicit their thinking on how the epidemic was halted.
An article from the WHO discusses how the epidemic was halted by "Detecting and breaking every chain of transmission." It also raises a cautionary warning that because the Ebola virus remains in the semen and eye fluids in some survivors, the WHO and other health and government organizations must remain vigilant for more outbreaks and be prepared to stop them before they spread.
Going Further: John Snow and the Scourge of London
As an enrichment activity, have students read this article, which introduces students to the first big idea of epidemiology: finding the source of the disease, with the story of John Snow and his investigations of cholera in 19th century London.
Snow’s hypothesis was that cholera was a waterborne disease and the source of the epidemic was a pump somewhere in the city. Except for the very wealthy, most Londoners during this time period obtained their water for drinking, washing, and food preparation from a town pump closest to where they lived. Snow’s goal was to prove his hypothesis by collecting evidence.
You may want to begin by discussing the idea that the first step in most investigations is the formulation of a hypothesis in which the researcher poses an explanation for an observed phenomenon. The next step is to devise a method for gathering evidence that will prove or disprove the hypothesis. Snow’s methods involved interviewing victims, their families and associates about their lives and habits and then looking for patterns in his data.
Additional Resources
Outbreak, Frontline.
FRONTLINE tells the vivid, inside story of how the Ebola outbreak began, and why it wasn't stopped before it was too late.
2014 Ebola Outbreaks, Healthmap.org.
This interactive timeline shows the spread of Ebola, starting with the first index cases in 2013 through the end of the epidemics in January of 2016.
Ebola and Contact Tracing, Centers for Disease Control and Prevention.
"This video describes contact tracing, a method used by CDC and partners to identify new Ebola cases quickly and isolate patients as soon as they show symptoms, preventing spread to others. The video demonstrates how even one missed contact can keep Ebola spreading and that careful tracing of contacts and isolating new cases can stop the outbreak."
Contact tracing means finding everybody who has come in contact with an infected person. In the case of Ebola, contacts are watched for 21 days. If they become sick they are isolated and contact tracing with that person begins again.