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Infectious Disease
What You Should Know
Chapter 12.1
Infectious Disease
• Diseases caused by microorganisms living in or on humans,
animals, or plants.
• Microorganisms also known as Pathogens
• Pathogenic microorganisms include certain bacteria, viruses,
fungi, protozoa, and worms.
• Infectious diseases are also called… Communicable Disease –
pathogens are transmitted from one living thing to another.
Signs and Symptoms
• The presence of a disease is detected by observing signs or
symptoms.
• SIGNS – Objective evidence of disease that can be outwardly
observed or measured: fever, pulse, skin color, breathing rate.
• SYMPTOMS – subjective evidence for a disease because the
evidence is based on feeling instead of outwardly measurable
indicators of illness.
Predictable Course of Infections
• Incubation Period – the time between the pathogen’s
entrance into the body and the first appearance of symptoms.
• Mild to no symptoms
• Still contagious
• Possible of spreading
• Clinical Stage - Signs and symptoms of a disease arise and are
most prominent.
• Toxins produced
• Immune response reaches it’s height
• Convalescent Stage – signs and symptoms of a disease fade
and a person is no longer contagious.
Bacteria
• Single-celled organisms living in nearly every possible place
that cans sustain life.
• Most are helpful – large amounts live on the body’s surface
and in the digestive tract.
• Examples of bacteria – E. coli, Staph infections, MRSA,
pneumonia.
Virus
• A pathogen that infects cells and uses their enegy because it
cannot reproduce or grow on its own.
• Entirely dependent on other cells. Uses the cells resources
and energy for growth.
• Scientist do not consider viruses to be living organisms.
Fungi
• Much more complex than bacteria and viruses. Built from
larger cells.
• Few fungi cause disease and many are beneficial. Penicillin (a
life-saving drug) is made from the mold penicillium notatum.
• Few fungi cause disease in humans… Mycosis is a fungal
infection that usually attacks damaged tissues or weakened
people.
Parasites
• Parasites – an organism that must live inside or on another
living thing, where they cause damage and disease.
• Protozoa – single celled organisms that are larger and more
complex than bacteria, and which may cause disease.
• Worms – multicellular organisms with specialized tissues and
organs that can be transmitted to humans in water or food
that has been contaminated.