NOVA scienceNOW: 1918 Flu
Compare bacteria and viruses. Flu is caused by a virus. To understand
how flu spreads, infects a host, and can be prevented, it is important to
understand some key facts about viruses and how they compare to bacteria,
microorganisms that are also responsible for many infectious diseases. Discuss
the following characteristics with students.
(a nanometer is a billionth of a meter)
to 400 nanometers. Average size is less than 100 nanometers
be 10-100 times larger than the largest virus, ranging from 400 to thousands of
nanometers. Average size is 2,000 nanometers
a range of animal and plant tissues as well as single-cell organisms, including
bacteria. Once in a host, viruses usually target very specific tissues.
infect a wide range of plant and animal tissues but cannot infect viruses
to antibiotics. Antibiotics target specific kinds of bacteria. Some bacteria
are resistant to certain antibiotics.
to use another organism's cell reproduction mechanisms (i.e., the host's
DNA/RNA) to reproduce
without using the DNA and RNA of other cells
structure consisting of a core of reproductive molecules (DNA/RNA) surrounded
by a protective protein coat
unicellular structure containing a variety of organelles for different
functions (e.g., energy production, reproduction, protein synthesis)
Examine how viruses are transmitted. Ask students how they think
microbes travel from person to person and what behaviors can minimize
transmission. List student responses on the board and have the class sort the
responses into categories. (Microbes can be transmitted by contact [e.g.,
blood, body fluids, and contaminated surfaces], aerosols [e.g., droplets from
coughing and sneezing], and ingestion [e.g., food or water].
Inoculations, wearing masks, washing hands, and following safe sex practices
can limit exposure and possible infection.) Ask students to name animals
that harbor viruses that can also infect humans. (Examples include yellow
fever [spread by mosquitoes from monkeys to humans], rabies [caused by a
rhabdovirus that can jump species barriers fairly easily among mammals],
certain flu viruses [found in the guts of birds and which can infect pigs as
well], West Nile virus [carried by birds], and Eastern equine encephalitis
(EEE) [found in birds and horses].)
Discuss how immunizations protect people against viruses. Review in
general terms how the immune system works. Then, list the following terms on
the board: virus, detects, immune system, antibodies, white blood cells,
destroy, and eliminate. Ask students to incorporate the terms into a short
paragraph describing how the immune system eliminates a pathogen, such as a
virus, from the body. Then, discuss how inoculations work to protect a person
against infection. (A sample paragraph could be: When a virus enters the
body, the immune system detects the invading virus and begins to produce
antibodies against it. These antibodies flag the virus as a foreign particle.
White blood cells then proceed to destroy and eliminate the flagged
Immunizations essentially trick the body's immune system into creating
antibodies against a specific virus. They work by introducing a weakened or
inactivated form, or sometimes a small piece, of a virus into the body. The
injected virus is not viable and cannot make a person sick, but it does kick
the immune system into action. The immune system responds by producing
antibodies against the invading virus. If a person is then exposed to the virus
at a later time, the antibodies needed to destroy it are already present in the
body. Once a person has antibodies against a specific viral disease, such as
flu or measles, these antibodies continue to circulate in the blood, and he or
she remains immune to infection from that virus, in some cases for
Discuss the cyclical nature of seasonal flu outbreaks. Ask the class
why flu outbreaks are more common and severe in the late fall and winter than
in the summer. List students' ideas on the board. Ask what kinds of tests they
could run or data they could collect to support their ideas. (One accepted
explanation is that, in cold weather, people use heating systems that
recirculate air. This increases the likelihood that people will be exposed to
viruses carried in the recirculating air. During cold weather, people also
congregate indoors more, which brings them in close proximity to one another.
Tests students could run and supporting data they could collect include
comparing the number of flu cases in:
- summer and winter for a specific region
- areas with severe winters versus areas with mild winters [e.g., Minnesota and Florida]
- the month of January in the Northern and Southern hemispheres.
- sparsely populated rural areas versus congested urban areas.)
Determine how quickly an epidemic would sweep through your community. In
this day and age of air travel, crowded cities, and large buildings with
heating and cooling systems that recirculate air, a highly infectious virus can
sweep through a population more easily than ever before. To help students
understand the number of factors involved in the spread of an epidemic and the
complexities of how these factors interact, have them try the following
simulation. Have students find the number of people in your area and estimate
how quickly a highly contagious flu virus could infect half the population. To
make this estimate, the class will need to develop a scenario and define
certain parameters to break an epidemic down into its component pieces.
Everyone could use the same set of factors, or groups could come up with their
own. For example, students should:
determine how the virus enters your community (e.g., a family of six brings the virus to town).
define how the virus is transmitted from person to person (e.g., through droplets from coughing and sneezing).
decide how long it takes for an infected person to show symptoms and get sick after having been exposed to the virus (e.g., it takes four to ten days to incubate).
establish for how long a person is contagious (e.g., up to five days after symptoms first appear).
determine what percentage of the population is inoculated.
consider how often people gather in large crowds in your area.
A wide range of possibilities exists for each of these factors. Even among
public health experts, there are ongoing debates about the factors to include
in a model. The intention is not to have students make accurate predictions but
rather to get a discussion going about the nature of an epidemic. Students
should share their estimates of how long it will take for 50 percent of the
population to fall ill. Have them explain how they arrived at this
Explore different public health strategies used to manage a recent
epidemic. Public health workers use four general strategies to manage an
epidemic: quarantine, immunization, education about disease prevention, and
early, aggressive treatment of ill people. Divide the class into groups and
have each team create a poster about a disease that has recently been the news.
Examples are West Nile virus, Legionnaire's disease, AIDS, SARS, and Ebola. In
the poster, have students:
- describe the disease and how it is transmitted.
- find out when and where it was first observed.
- summarize how public health workers managed (or are managing) the outbreak.
- describe how the disease affected (or affects) people and communities.
- list preventive measures people can follow to avoid infection.
Debate the ethics of quarantining. Quarantining is considered an
important tool in stopping an epidemic and was used by the Chinese government
during the SARS epidemic. Though it restricts personal freedom, quarantining
keeps potentially infectious people separated from uninfected people. As a
class, explore the ethical implications of quarantining. To prepare for the
debate, assign students roles that represent different voices in the community,
such as a public health worker, a sick person who cannot afford to miss work, a
business owner, a firefighter, a hospital worker, a child whose parent is sick,
and a town mayor. Have students debate the issue from the vantage point of
their character, representing the character's views as well as possible. The
practice of quarantining may be a sensitive issue for some students, such as
those having personal or family experiences with illnesses like HIV/AIDS,
whooping cough, or flu. If you suspect this may be the case for some of your
students, consider having the debate without assigning specific roles.
Research past epidemics. Divide the class into groups and assign each
one an epidemic listed in the Example of Major Epidemics table (below) to
research. Have each group create a poster that includes the following
information: date, location, how it began and spread, estimated death toll, and
some social, cultural, and political effects of the epidemic.
Examples of Major Epidemics
disease described by Hippocrates.
by smallpox or Bubonic Plague. Death toll unknown but extensive. Occurred
during the reign of Marcus Aurelius Antoninus (121-180 A.D.), who died in the
epidemic. Waxed and waned until 266 A.D..
Plague, caused by species of Yersinia bacteria. Occurred during reign of
Justinian. Thought to have led to the demise of the Western Roman Empire.
Plague (3 varieties). Killed an estimated 25-50% of population. Brought to
Europe by Tartars from China.
and measles. Killed 90% of Native Americans. Brought by conquistadors and
greatly magnified the widespread impact of the conquest.
Unknown numbers of dead in many parts of the world. First recorded flu epidemic.
Death toll unknown. Recurred in Boston several times (1687, 1713, 1729, 1739)
and in other locations in pre- and post-revolutionary U.S.
fever, caused by Flavivirus. Infects humans, most monkey species, and several
small mammals. Spread by mosquito. Highly preventable with very effective
USA, and then spread worldwide in three waves.
caused by the H1N1 avian flu virus. Killed 30-50 million people worldwide.
Also called the Spanish Influenza epidemic, but no special connection to Spain.
Carried by troops moving around at the end of the war.
Flu. Killed 2 million worldwide. Thought to have been caused by a new A/H2N2
Kong Flu. Killed 1 million worldwide. Caused by H3N2 - was similar to the 1957
flu virus and therefore many populations had some immunity.
Immunodeficiency Virus (HIV). As of 2006, killed 22 million people and infected
over 38 million. Causes the disease acquired immune deficiency syndrome (AIDS).
Notable for its ability to mutate and thereby confound attempts to create a
appeared in China in November 2002. Spread worldwide to 26 countries.
Acute Respiratory Syndrome (SARS), caused by a coronavirus. Gave rise to 8,000
cases and 800 deaths, usually associated with pneumonia or common cold. Was
stopped by effective quarantine measures.
HHMI Online Companion
The Howard Hughes Medical Institute offers an extensive collection of pandemic-flu resources in its online companion to this episode of NOVA scienceNOW.
More on HHMI and its partnership with NOVA
Web Focus: 1918 influenza pandemic
This Web site from the science journal Nature provides a number of articles and other resources for current research on the 1918 flu.
The Centers for Disease Control and Prevention provides answers to frequently asked questions about its work with the 1918 flu virus.
Find information on health safety, planning, research activities, and more on the U.S. government's official Web site on pandemic flu and avian influenza.
The Deadly Virus: The Influenza Epidemic of 1918
In this online exhibit from the National Archives and Records Administration, view scanned photographs and other documents from the 1918 flu pandemic.
On this companion Web site to the American Experience program "Influenza 1918," see a time line of events, read interviews with show participants, and more.
America's Forgotten Pandemic: The Influenza of 1918
by Alfred W. Crosby. Cambridge University Press, 2003.
Devil's Flu: The World's Deadliest Influenza Epidemic and the Scientific
Hunt for the Virus That Caused It
by Pete Davies. Owl Books, 2000.
Smart Mice, Not-So-Smart People: An Interesting and Amusing Guide to Bioethics
by Arthur L. Caplan. Rowman & Littlefield, 2007.
"Unmasking the 1918 Influenza Virus: An Important Step Toward Pandemic
Influenza Preparedness," a joint statement by Anthony Fauci, Director, National
Institute of Allergy and Infectious Disease, and Julie Gerberding, Director,
U.S. Centers for Disease Control and Prevention, October 5, 2005
"Why Revive a Deadly Flu Virus?"
by Jamie Shreeve. The New York Times Magazine, January 26, 2006.