Influenza Virus: A tiny moving target (Page 1 of 2)

Level: High School

Time: 2-3 50 minute periods


The potential of a new flu pandemic is a frightening idea. This curriculum explains how influenza viruses infect cells and replicate. It also has students explore where influenza viruses come from, how viruses change, and why some become deadly.

Table of Contents:

Background for Teachers

About the Lesson

National Science Standards


Lesson (Page Two)

Transparencies/Handouts (Page Two)

References (Page Two)

Click here to view "The influenza virus life cycle", an interactive presentation.

Background for Teachers

Influenza viruses are always with us, constantly changing and causing misery each flu season. Most of the time they knock people off their feet for a week or two but sometimes the flu can be dangerous or even fatal. Immunocompromised people, those who are already sick, or those whose immune systems are weak such as young children and older people, are hit hardest by the flu. This version of the flu is with us every year and we are accustomed to it, however the threat of a flu pandemic is a much larger problem and rightfully causes a great deal of concern.

Flu pandemics emerge in a cycle and the world is overdue for the next one. If the avian H5N1 virus doesn’t cause the next pandemic, another strain will. There were three pandemics in the 1900’s: 1918, 1957, and 1968. In 1918, 30-40 million people died world wide (For more information, see Reference 1). We know much more about influenza now than we did in 1918, and the hope is that we can use this knowledge to prevent or control a serious pandemic (Ref. 2). Pandemics occur when a virus acquires the ability to infect a new host and spread rapidly through the population. How this occurs is more easily understood when the normal replication cycle of the virus is understood.

Influenza viruses come in three types: A, B, and C. All three can infect humans, but the most common infection is by type A. Type A viruses are classified in subtypes based on two proteins that stick out from the surface. These are hemagglutinin (H), which is responsible for initiating entry into the host cell, and neuraminidase (N), which is involved in release of new viral particles from the infected cell. There are 16 varieties of hemagglutinin and 9 of neuraminidase. Subtypes are named by which version of hemagglutinin and neuraminidase, such as H1N2 a common version in humans. The virulence and pathogenicity of the virus depends on the combination of hemagglutinin and neuraminidase.

Influenza viruses are normally found in wild waterfowl. The H5N1 avian version is particularly deadly in its normal host, wild birds. It is easily transferred to domestic birds, and from there has occasionally infected humans, particularly those who came in close contact with infected birds. It appears to be very dangerous in humans as well, but that may be due to reporting. Work in Turkey has revealed people who were infected with H5N1, but did not get sick enough to require medical attention. At the same time, other people in Turkey have died of the disease.

In order for H5N1 to develop into a pandemic, it must acquire the ability to transfer rapidly between and effectively infect human hosts. Once that occurs, it will be difficult to control the spread of the disease. Our global society ensures wide dispersal of diseases via air travel, and the incubation period for the flu is short. This means that by the time health officials recognize an outbreak, it will already have spread beyond the original area. However, we understand influenza much better now than we have in previous pandemics. We are better equipped to prevent transmission of the virus, have antiviral medications to treat infections, and are working to develop effective vaccines. For more information on influenza viruses and pandemics, see References 3, 4, and 5.

The control of influenza relies on basic evolutionary theory. The development of the annual flu vaccine is based on our understanding of antigenic drift – or change over time. We expect new strains to arise as viral polymerases make mistakes during replication. We can predict the direction of change based on the trends observed in the virus genome over the course of the flu season, and prepare our immune systems with a vaccine. The vaccine is developed with the latest version of the flu so that when the “real thing” shows up in our bodies, the immune system has seen it or something similar and can effectively fight it off. Pandemics occur because our immune system cannot cope with invasion by a completely new viral type and these viruses often infect more cell types than the “normal” flu virus. Pandemic viruses avoid detection by the immune system, cause massive damage in the host, and spread rapidly. Pandemics die down because any pathogen that kills its host before replicating and spreading dies with the host. A milder version of the disease is more likely to allow continued dispersal of the virus and so viral strains causing less intense symptoms will have a selective advantage. In previous pandemics, the virus became less dangerous after 18-24 months. However, incredible damage was done during that brief time.

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About the Lesson

This lesson is structured using the BSCS 5E model. In this model, students are first Engaged, in this case by presenting them with a game modeling viral infection. Once the students are interested, they move to combined Explore and Explain sections where they have an opportunity to learn about viral structure and replication. Students then move to an Elaborate section, in which they apply the information they have just learned at a more advanced level to explore how viruses evolve. Evaluation can be conducted throughout the inquiry based lesson, but a formal evaluation opportunity is suggested in the form of presentations or written reports in which students are asked to use their understanding of the virus to suggest ways in which to prevent or treat infection.

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National Science Standards

Content Standard A. Abilities Necessary to do Scientific Inquiry

Communicate and Defend a scientific argument

  • Reviewing information, expressing concepts, constructing a reasoned argument.

C: Life Science

The Cell

Molecular Basis of Heredity

Biological Evolution

Interdependence of Organisms

  • Cells have particular structures that underlie their functions. Every cell is surrounded by a membrane that separates it from the outside world. Inside the cells in a concentrated mixture of thousands of different molecules which form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules and the storage of genetic material.
  • In all organisms, the instructions for specifying the characteristics of the organism are carried DNA.
  • Changes in DNA occur spontaneously at low rates. Some of these changes make no difference to the organism, whereas others can changes cells and organisms.
  • Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources requires for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
  • The millions of difference species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors.
  • Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.
  • Human beings live within the world’s ecosystems.

Content Standard F: Science in Personal and Social Perspectives

Personal and Community Health

  • The severity of disease symptoms is dependent on many factors, such as human resistance and the virulence of the disease-producing organisms. Many diseases can be prevented, controlled, or cured.

Content Standard G: History and Nature of Science

Science as a Human Endeavor

  • Scientists are influenced by societal, cultural, and personal beliefs and ways of viewing the world. Science is not separate from society but rather science is a part of society.
  • Occasionally, there are advances in science and technology that have important and long-lasting effects on science and society. Examples of such advances include the geologic time scale and biological evolution.

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  • Prepare the following for “Gotcha!”:
    • 2 tokens per student
    • 1 slip of paper per student stating cell type (virus, respiratory, lung, immune, other organs as needed). Keep a ratio of 1:1:1:1:1, so in a class of 30, there will be 6 viruses, 6 respiratory cells, 6 lung cells, 6 immune cells, and 6 other organs.
    • Write a password on each slip. Give the viruses at least three different passwords (ie. Blue, turtle, apple). Give all the respiratory cells one of the viral passwords (ie. Blue). Give one lung cell a viral password, and give the others completely different passwords. Give the immune cells two out of three passwords in different combinations (ie. Blue and turtle, blue and apple, turtle and apple). Give one of the other cell types a viral password and the others completely different passwords.
  • For the viral structure lesson, prepare one set of the following materials for each group:
    • 1 plastic egg
    • 8 one inch strips of black yarn
    • 8 half inch pieces of drinking straw
    • 8 paper clips or buttons that can slide on the yarn
    • 15-20 “dots” of Velcro (soft side), made with a hole punch
    • 15-20 grains of rice.


  • If desired, make enough copies of Master 1.1 Cell Surfaces for groups of two to three students. You may wish to laminate these if you want to use them repeatedly. Prepare the Master 1.1 Cell Surfaces by gluing the opposite side of the Velcro “dots” from the virus structure on the “respiratory tract”. Glue paper or cloth dots to the other cell surfaces.
  • Make one copy per group of Figure 1. Influenza Virus for the structure exercise.
  • Make one copy per student of Master 1.2 Classifying Influenza Viruses.
  • For each group prepare two sets of 3X5 cards. Label the cards on one side in blue ink with HA, NA, PB1, PB2 PA, M, NP, NS. On the other side of the card write the name of the corresponding protein. For one set write the name in black ink; write the name in red ink on the other set.
    • Hemmagglutinin (HA)
  • Neuraminidase (NA)
  • PB1 (polymerase)
  • PB2 (polymerase)
  • PA (polymerase)
  • M1/M2 (coat protein)
  • NP (nucleocapsid)
  • NS1/NS2 (nonstructural proteins)
  • Assure access to computers in teams of two or three students.

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