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What You Need to Know
Essential Standard: 8.L.1 Understand the structure and hazards caused by
agents of disease that effect living organisms.
Clarifying Objective: 8.L.1.1 Summarize the basic characteristics of viruses,
bacteria, fungi and parasites relating to the spread, treatment and prevention of
disease.
Students need to know:
 microbiology as a basic science explores microscopic organisms
including viruses, bacteria, protozoa, parasites, and some fungi and algae.
These organisms lack tissue differentiation, are unicellular, and exhibit diversity of
form and size.
 viruses, bacteria, fungi and parasites may infect the human body and
interfere with normal body functions. Some kinds of bacteria or fungi may
infect the body to form colonies in preferred organs or tissues.
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Viruses
 Viruses are non-living particles composed of a nucleic acid (DNA or RNA)
and a protein coat.
 Viruses need a host cell to reproduce.
 Viruses invade healthy cells and use the enzymes and organelles of the
host cell to make more viruses, usually killing those cells in the process.
 Viral diseases are among the most widespread illnesses in humans. These
illnesses range from mild fevers to some forms of cancer and include
several other severe and fatal diseases. Transmission of these illnesses
varies; some are transmitted by human contact, while others are
transmitted through water or an insect bite.
 Vaccines and some anti-viral drugs are used to control and prevent the
spread of viral diseases.
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Bacteria
 Bacteria are prokaryotic single-celled organisms.
 Bacteria can live in a variety of places (with oxygen, without oxygen,
extreme hot, extreme cold).
 Bacteria reproduce through binary fission, a form of asexual reproduction.
Under optimal conditions, bacteria can grow and divide extremely rapidly,
and bacterial populations can double very quickly.
 Antibiotics are used to inhibit the growth of bacteria. Because antibiotics
have been overused, many diseases that were once easy to treat are
becoming more difficult to treat. Antibiotic resistance in bacteria occurs
when mutant bacteria survive an antibiotic treatment and give rise to a
resistant population.
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Fungi
 Fungi can sometimes attack the tissues of living plants and animals and
cause disease. Fungal disease is a major concern for humans because
fungi attack not only us but also our food sources, making fungi
competitors with humans for nutrients.
 Mold spores can cause mild to serious allergies in some people. Billions of
mold spores can become airborne and may then be inhaled, triggering an
allergic reaction.
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Parasites
 A parasite is an organism that feed on another individual, known as the
host. They either live on or in their host’s body.
 Natural selection favors adaptations that allow a parasite to efficiently
exploit its host. Parasites are usually specialized anatomically and
physiologically. Tapeworms are so specialized for a parasitic lifestyle that
they do not even have a digestive system. They live in the small intestine
of their host and absorb nutrients directly through their skin.
 Infectious disease may also be caused by animal parasites, which may
take up residence in the intestines, bloodstream, or tissues.
BOTTOMLINE: Microbiology as a basic science explores microscopic organisms including
viruses, bacteria, protozoa, parasites, and some fungi and algae. These organisms lack tissue
differentiation, are unicellular, and exhibit diversity of form and size. Viruses, bacteria, fungi
and parasites may infect the human body and interfere with normal body functions. A person can
catch a cold many times because there are many varieties of cold viruses that cause similar
symptoms. Viruses are not considered to be alive but they affect living things. Viruses need a
host cell. AIDS, influenza, the common cold, polio, chicken pox, small pox, yellow fever, viral
meningitis, West Nile and Ebola are caused by viruses. Rabies, Lyme Disease, bacterial
meningitis, and Leprosy are caused by bacteria. Bacteria are very small organisms, usually
consisting of one cell, that lack chlorophyll. Except for viruses, they are the smallest living things
on Earth. Bacteria are found everywhere, in the air, soil, water, and inside of your body and on
your skin. They tend to multiply very rapidly under favorable conditions, forming colonies of
millions or even billions of organisms within a space as small as a drop of water. Bacteria are
generally classified into three groups based on their shape: spherical, rodlike, spiral or
corkscrew. We have antibiotics to help with bacterial infections and vaccines to help with taking
care of viruses that cause infections.
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Essential Standard: 8.L.1 Understand the structure and hazards caused by
agents of disease that effect living organisms.
Clarifying Objective: 8.L.1.2 Explain the difference between epidemic and
pandemic as it relates to the spread, treatment and prevention of disease.
Students need to know:
 a disease outbreak happens when a disease occurs in greater numbers
than expected in a community or region, or during a season.
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An outbreak may occur in one community or even extend to several
countries. It can last from days to years. Sometimes a single case of a
contagious disease is considered an outbreak. This may be true if it is an
unknown disease, is new to a community, or has been absent from a
population for a long time. An outbreak can be considered as an epidemic or
pandemic.
 epidemic and pandemic are similar terms that refer to the spread of
infectious diseases among a population.
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There are two main differences between epidemic and pandemic. The term
pandemic normally is used to indicate a far higher number of people affected
than an epidemic. Pandemic also refers to a much larger region being
affected. In the most extreme case, the entire global population would be
affected by a pandemic.
 the terms epidemic and pandemic usually refer to the rate of infection,
the area that is affected or both.
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An epidemic is defined as an illness or health-related issue that is showing up
in more cases than would normally be expected. It occurs when an infectious
disease spreads rapidly to many people. In 2003, the severe acute
respiratory syndrome (SARS) epidemic took the lives of nearly 800 people
worldwide.
 in the case of a pandemic , even more of the population is affected than
in an epidemic.
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A pandemic typically is in a widespread area (usually worldwide) rather than
being confined to a particular location or region and affect global populations.
An epidemic is not worldwide. For example, malaria can reach epidemic
levels in regions of Africa but is not a threat globally. Whereas a flu strain
can begin locally (epidemic) but eventually spread globally (pandemic). This
is not unusual for a new virus, because if people have not been exposed to
the virus before, their immune systems are not ready to fight it off, and more
people become ill. Swine flu started in Mexico City where it was feared to
lead to epidemic proportions in North America, now that the flu has been
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found in New Zealand, Israel, Scotland and many other countries, it has
become pandemic. The 1918 Spanish flu and the Black Plague are extreme
examples of pandemics. Keep in mind, though, that a pandemic doesn't
necessarily mean millions of deaths-it means a geographically widespread
epidemic.
 influenza pandemics have occurred more than once.
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Spanish influenza killed 40-50 million people in 1918. The Asian influenza
killed 2 million people in 1957. The Hong Kong influenza killed 1 million
people in 1968. An influenza pandemic occurs when: A new subtype of virus
arises. This means humans have little or no immunity to it; therefore,
everyone is at risk. The virus spreads easily from person to person, such as
through sneezing or coughing. The virus begins to cause serious illness
worldwide. With past flu pandemics, the virus reached all parts of the globe
within six to nine months. With the speed of air travel today, public health
experts believe an influenza pandemic could spread much more quickly. A
pandemic can occur in waves. And all parts of the world may not be affected
at the same time.
Teacher Note:
It is not necessary for students to know specific examples of epidemics and
pandemics. Examples provided are for teaching purposes only.
Vectors are mechanisms (other than a person) that spread disease without getting
sick itself. Rats, ticks, mosquitoes, and soil are examples of vectors. An infectious disease is one
that can be passed from one generation to another. Scientists study microbial pathogens (disease
causing agents), to find methods for prevention and treatment of disease. Improvements in public
health depend upon state-of-the-art biomedical research to explain how microbes cause
infectious diseases in both plants and animals. To analyze data, scientists use various techniques
and strategies including computer modeling, cell culture, animal models, and clinical trials in
humans. Safe handling and hygiene as well as various antimicrobial chemicals can be used to
reduce the risk of and the treatment of these infections. Industrial microbiology involves quality
control in preventing growth and contamination of products leading to food spoilage, and the
production of pharmaceuticals. The health of humans and earth depends on microbes. An
epidemic is an outbreak of a disease that affects a disproportionately large number of
individuals within a population, community or region at the same time (example-typhoid).
Pandemic is an epidemic of an infectious disease that is spreading through human populations
across a large region, continent or even worldwide (examples smallpox, tuberculosis, flu of
2009).
BOTTOMLINE:
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