Biology

Innate Immunity: Fighting Ebola

With currently no approved drugs or vaccine for the Ebola virus, the more we understand about how the body fights this pathogen naturally, the better our chance of synthesising a treatment.

In this lesson you will investigate the following:

• What causes infectious disease?

• How do we protect ourselves from microscopic invaders?

• How does the innate immune response tackle viruses?

• When is fever helpful?

Aaaahhhhchoooo! Find out what your immune system is doing when you don’t feel like doing anything.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com

Introduction: Innate immunity (P1)

Dying from Ebola virus disease is a truly awful experience. First you get a fever and feel exhausted. Your muscles ache. Youhave a headache and a sore throat. Then you get diarrhoea and start vomiting. In some cases the virus destroys your blood vesselsand you start bleeding from your nose, eyes and ears.

Where did this terrible infectious disease come from?

The first known human cases of Ebola occurred in 1976 in Sudan and the Democratic Republic of Congo. Scientists think thathumans first contracted the disease from bats that carry the viral pathogen. Many poor people in Africa eat bats and any other“bush meat” they can find in the jungle.

Fortunately the disease doesn’t affect humans all the time. An outbreak spreads, it kills many people, but then disappears,sometimes for years.

But the current outbreak, which has killed nearly 6,000 people, is still going on.

People catch Ebola when the virus enters their bodies through broken skin or through mucous membranes, like in your nose ormouth.

So far there is no treatment or vaccine to protect people from the virus, and so world health authorities can only try to control thedisease – preventing new cases by separating the sick from the healthy.

That is harder in poor countries like those in West Africa than developed countries that have better roads and communicationssystems. In Africa, many people live in remote areas where it is hard for the authorities to know what is going on.

Now the race is on to find both a treatment that will help more people survive the disease (at the moment about half of the peoplewho contract the disease die from it) and also to find a vaccine, that will stop people catching it in the first place.

Read or listen to the full Cosmos magazine article here.

Question 1

Speculate: Ebola is a re-emerging infectious disease. There are many other infectious diseases that are either emerging or re-emerging, as depicted in the map above.

Describe some of the factors you think might be responsible for emergence or re-emergence of a disease.

Gather: Innate immunity (P1)

While all microscopic, microbes come in all sorts of shapes and sizes. Viruses (left) are the smallest and need otherorganisms to reproduce. Bacteria (middle) and protozoa (right) are larger than viruses and can reproduce by themselves.

Do you notice any other differences?

Pathogens are micro-organisms or microbes (organisms too small to be visible to the naked eye) that cause infectious disease. Themost common infectious disease-causing microbes are bacteria, viruses, fungi, and protozoa (a type of parasite).

Pathogens

Question 1

Research: The illustration below shows four infectious diseases (left) and four microbe types (right). Draw lines to connect eachinfectious disease with the microbe type responsible for it.

Hint: A simple internet search will help you.

Did you know?

Not all microbes cause disease. Millions of microbes live on and inside our bodies without us even noticing and some types ofmicrobes are even helpful. In Cosmos lesson 19 you can learn about the important ecosystem of microbes existing in our bowels.

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Question 2

Recall: Why does a virus need another cell for its growth?

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Question 3

Explain: The video clip showed that viruses have "keys" (ligands) and that cells have "locks" (receptors). Explain why it is essentialfor the ligand on a virus to bind to a specific cell receptor for a virus to infect it.

So when a virus gets inside you and infects one cell, millions of new ones come out of it. Then each of those new viruses do thesame. Wouldn't that eventually kill you? Well it would, if it weren't for your immune system.

Your body is constantly being exposed to disease-causing microbes. Fortunately your immune system responds to any object, suchas a pathogen, that it considers as foreign or ‘non-self’. In simplest terms, your body’s defence to pathogens can be divided into twotypes – the innate and adaptive immune systems.

The innate immune system refers to the first line of defence of a host against a pathogen. It includes physical and chemical barriersto infection – non-specific defences ready and waiting to stop infections before they can set in.

The adaptive immune system refers to the final line of defence against a pathogen. It involves the production of specialised cells andchemical substances called antibodies that target pathogens that managed to survive the innate immune system.

Even though all viruses want to spread, many viral infections are prevented by the innate immune system. Some of these innatedefence strategies are always in place including the skin and phagocytic cells; whereas others are triggered by an infection, such as

The immune system

Innate immune system response to viruses

fever and inflammation.

The skin

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Question 4

Calculate: The outermost layer of your skin (stratum corneum) consists of about 15 layers of dead cells. Together these cellsmeasure approximately 0.0002 cm in thickness and yet, if intact, these cell layers are an excellent first line of defense againstpathogens. Given that a typical A4 piece of paper is approximately 0.1 mm thick, calculate how many times thinner the stratum

corneum is than A4 paper.

Phagocytic cells

Question 5

Sequence: Phagocytosis refers to the process by which an immune system cell engulfs a pathogen and digests it, thereby destroyingit. The graphic below illustrates the process of phagocytosis by a phagocytic cell (also known as a phagocyte). Use the information inthe graphic to sequence the stages (1-5) of virus phagocytosis.

Sequence Stages of phagocytosis

Virus is destroyed by enzymes

Phagocyte engulfs virus and traps it in a phagosome

Waste is released from phagocyte

Receptors on phagocyte recognise virus ligands as foreign molecules

Phagosome fuses with lysosome sac which contains powerful enzymes.

Inflammation

Viral infection can trigger the release of cytokine molecules. These molecules trigger inflammation by changing the permeability(leakiness) of surrounding blood vessels and so allow more immune system cells, such as phagocytes, to access the site of infection.As more and more cells and fluid from the blood vessels enter the surrounding area, the area becomes red, swollen and hot – wecall this response inflammation.

Question 6

Compare: The graphic on the left illustrates a normal blood vessel, while the graphic on the right shows the same blood vesselduring an inflammatory response. Draw green arrows to point to three changes that have occurred in the inflamed bloodvessel and use the green text tool to describe each of these changes in your own words.

Fever

Fever refers to a prolonged increase in your core body temperature above the normal range of 36.5–37.5°C. Many viruses, and otherhuman pathogens, replicate best within host cells at a temperature of 37°C. So to fight them off your body raises its temperature sothat it is too hot for the viruses to survive.

The following data tracks the core body temperature of a person during the course of a virus infection.

Time following virus infection (hours) Core body temperature (°C)

0 36.5

1 37.0

2 36.5

3 38.0

4 39.4

5 40.1

6 41.0

7 41.0

8 40.6

9 39.0

10 38.0

11 37.1

12 36.6

Question 7

Plot: Visualise the change in temperature over time above by plotting the above data as a smooth line.

Hint: Be sure to label the x and y axes and to add a suitable title.

Title

X-Axis

auto

Y-A

xis

36 auto auto

Series 1

x y

This graph needs some data!

Question 8

Analyse: How many hours following infection by the virus did the fever begin and approximately how long did it last?

Question 9

Summarise: What innate immune system processes occur in the body in response to infection by a virus?

Process: Innate immunity (P1)

Ebola

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The Cosmos article “Ebola: no quick solutions” points out that there is currently no cure or approved treatment for Ebola. Malaria,for which we do have a cure kills over 100,000 people per year while Ebola has only ever killed 7034 people in total.

Which infectious disease, Ebola or Malaria, do you think should receive more media attention?

Poll 1

Ebola

Malaria

No data to display.

Cum

ulat

ive

deat

hs

Days since first reported deaths

Cumulative mortalities from Ebola 2014

0k

1k

2k

3k

4k

5k

0 25 50 75 100 125 150 175 200

Question 1

Interpret: Which of the following best describes the trend line of the above line graph?

Exponential

Logarithmic

Linear

Question 2

Calculate: Complete the following table by calculating the time (in days) for the number of mortalities to double.

Days since first reported death Number of deaths reported Time (in days) for number ofmortalities to double

76 250 N/A

105 500 29

139 1000

162 2000

198 4000

Question 3

Calculate: Determine the mean average time (in days) for number of mortalities to double.

Question 4

Predict: Using your above calculations, use the table below to calculate the number of days that it would take for the number ofEbola deaths to reach more than 100,000 if the current mortality rate stays constant.

Days since first reported death Mortalities

198 4000

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Having done the above calculations have you changed your mind?

Vote again: Which infectious disease, Ebola or Malaria, do you think should receive more media attention?

Poll 2

Ebola

Malaria

Question 5

Reflect: The World Health Organisation has claimed that “Busting the myths about Ebola is crucial to stop the transmission of thedisease”.

What roles do you think that journalists and science communicators should play in tackling the Ebola outbreak?

Question 6

Discuss: A recent survey has revealed that almost a third of US adults get at least some of their news from Facebook. Someresearch scientists, who study how we communicate on social networks, say people are more likely to trust information that comesfrom people they know.

What advantages and limitations can you identify for communicating science news through social media? Add your thoughts to theclass discussion below.

Hint: If the class discussion is closed, ask your teacher to open it.

Apply: Innate immunity (P2)

Experiment: Modelling fever

The Cosmos article “Ebola: no quick solutions” outlines the signs and symptoms of Ebola disease. One of these symptoms is a highfever. Many scientists think that fever is an evolutionary adaptation to help survive pathogen attacks.

Yeast is a unicellular eukaryotic microbe. Some species can be pathogenic but the majority are useful. Healthy yeast cells carry out achemical process called fermentation, producing ethanol and carbon dioxide – the gas that makes bread rise and beer fizzy. Sugarsolution provides the nutrition and energy that yeast requires to carry out fermentation, however there is an optimum temperaturerange and fermentation drops off at temperatures outside this range.

Design an experiment to investigate the optimal temperature range for baker’s yeast (Saccharomyces cerevisiae) to carry outfermentation. The experiment is intended to model the response of a microbe to fever.

5 snack-sized zip-lock bags, each containing 2 g of baker’s yeast and 5 g of white sugar, labelled A - E

50 mL measuring cylinder

200 mL beaker

1000 mL beaker

Thermometer (0 – 110 C)

Hot water (approximately 80 C)

Cold water (approximately 10 C)

Ruler

Note: You may not need all these materials, and you may want to use some other materials as well.

Background

Aim

Materials

o

o

o

Independent variable (what you are changing): The temperature of water added to each zip-lock bag.

Dependent variable (what you are measuring): How much carbon dioxide is produced.

For your experiment you will need to consider each of the following points:

1. What temperatures should you test the yeast at?

2. How will you ensure that the water remains at approximately the temperature you choose?

3. How you will measure how much carbon dioxide is produced? (Hint: you can obtain an approximation by rolling the bags from the

top down and measuring the height of the gas – but you may be able to find a better technique.)

4. How long will you leave the yeast to ferment before you measure how much gas it has produced? Will you measure atdifferent time intervals or only once, at the end of the experiment?

5. How will you make sure that your experiment is controlled? That is, how you will keep the conditions in each of the zip-lockbags the same to ensure the reliability of the experiment?

6. What will be your hypothesis for this experiment?

Variables

Inquiry questions

Procedure

Question 1

Design: Write a step-by-step experimental method to show how you will test the effect of temperature on yeast fermentation.

Ask your teacher to approve your plan before carrying it out.

Question 2

Complete: Describe how you will measure the dependent variable. List the controlled variables and describe how you will controlthem.

Independent variable Dependent variable Controlled variables

The temperature of wateradded to each zip-lock bag.

Hypothesis

Question 3

Judge: Predict what you think the outcome of your experiment will be, and why, by writing a hypothesis.

Safety considerations

Question 4

Assess: Describe the potential hazards associated with the materials and method used in your experiment. How will you minimiserisk from these hazards?

Hazard Risk minimisation strategy

Results

Question 5

Collect: Use the project space below to present your results. Construct a table to suit the data, but also include photos, video orother representations as you see fit.

Discussion

Question 6

Justify: Explain why the same quantity of yeast and sugar was added to each zip-lock bag.

Question 7

Assess: Explain whether or not you think the yeast is affected bythe change in temperature of the water added to each zip-lockbag. Use your results to support your answer.

Question 8

Generalise: In science, a model may be used when it isimpossible to create the conditions necessary to investigate aconcept or theory. In what ways do you think this experimentmodels the response of a microbe to fever?

Question 9

Reflect: Identify some limitations of using this experiment tomodel the response of a microbe to fever.

Question 10

Evaluate: Suggest improvements that you could make if youwere to repeat this experiment.

Conclusion

Question 11

Conclude: Write a concluding statement addressing the aim and hypothesis of your experiment.

Career: Innate immunity (P2)

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Question 1

Imagine: Which aspect of being an immunologist would you enjoy the most? Which would you enjoy the least?

Cosmos Lessons team

Lesson authors: Hayley Bridgwood and Samantha WebberEditors: Jim Rountree and Bill CondieArt director: Robyn AdderlyEducation director: Daniel Pikler

Image credits: Kate Patterson / Medipics and prose, MirelaTufman and iStockVideo credits: National Academies, NPR, MinuteEarth, AFP NewsAgency, Kurzgesagt and YouTube