Lecture 7 — Infection, Virulence, and Epidemiology
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1
What is an infection?
The multiplication of microorganisms on or in a host.
2
Does infection always mean disease?
No. A host can carry microorganisms without becoming ill.
3
What is a disease?
A deviation from the host’s normal, healthy state.
4
How can normal microbiota help protect the host?
They can prevent disease-causing microorganisms from colonizing the body.
5
What is pathogenicity?
The ability of a microorganism to cause disease.
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What is a pathogen?
A microorganism capable of causing disease.
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What is virulence?
The degree of pathogenicity, or how severely a pathogen causes disease.
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What is an avirulent microorganism?
A microorganism that does not cause disease under the conditions being discussed.
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How can an avirulent bacterium potentially become pathogenic?
It can acquire genes associated with disease, including through horizontal gene transfer.
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What is a reservoir?
The source from which a disease-causing microorganism originates.
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What are examples of nonliving reservoirs?
Examples include contaminated water and soil.
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What is a portal of entry?
The route through which a pathogen enters a host.
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What is a portal of exit?
The route through which a pathogen leaves a host.
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Why must a pathogen have a suitable portal of entry?
It must reach the appropriate host tissue to establish infection.
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What is the infectious dose?
The number of microorganisms needed to establish an infection.
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Why does infectious dose matter?
A sufficiently large number of microbes may be needed to overcome host defenses.
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What are virulence factors?
Microbial features or products that help a pathogen cause disease.
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What are adhesins?
Microbial structures or molecules that help pathogens attach to host cells.
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Why are adhesins important?
They help pathogens remain attached rather than being removed by host defenses or physical processes.
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What is a biofilm?
A community of microorganisms attached to a surface and embedded in a surrounding matrix.
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How can biofilms help bacteria?
They promote attachment and can make bacteria harder for immune defenses and antibiotics to eliminate.
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What are extracellular enzymes?
Enzymes released by microorganisms that can help them invade tissues or obtain nutrients.
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What are toxins?
Substances that damage host cells or disrupt their functions.
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What is toxemia?
The presence of toxins in the blood.
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What are exotoxins?
Secreted protein toxins produced by Gram-positive or Gram-negative bacteria.
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What is the basic structure of an AB toxin?
A B subunit that binds to the host cell and an A subunit that disrupts a cellular process.
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How can you remember the functions of AB toxin subunits?
B binds; A attacks.
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How does the B subunit help an AB toxin enter a host cell?
It binds a specific host-cell receptor and promotes uptake of the toxin.
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What does the A subunit do?
It disrupts a cellular process after entering the host cell.
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What are membrane-disrupting toxins?
Toxins that damage host-cell membranes by forming channels or degrading phospholipids.
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What are superantigens?
Toxins that cause excessive immune activation and inflammation.
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How can superantigens harm the host?
The excessive immune response can damage host tissues.
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What is quorum sensing?
A process in which bacteria use chemical signals to sense population density and regulate gene expression.
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Why might a pathogen use quorum sensing?
It can coordinate the expression of virulence factors when enough bacterial cells are present.
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What is a pathogenicity island?
A region of a microbial chromosome containing genes associated with pathogenicity.
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What is direct contact transmission?
Transmission through direct physical contact between individuals.
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What is indirect contact transmission?
Transmission through contaminated objects or surfaces called fomites.
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What is a fomite?
An inanimate object that can carry and transmit infectious microorganisms.
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What is droplet transmission?
Spread through relatively large respiratory droplets that travel over short distances.
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How does airborne transmission differ from droplet transmission?
Airborne particles can remain suspended and travel farther through the air.
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What is a portal of exit example?
Respiratory secretions, saliva, blood, semen, or other bodily fluids can release pathogens from a host.
42
What is an endemic disease?
A disease that occurs at a relatively steady, expected frequency in a population or area.
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What is an epidemic?
A sudden increase in disease cases above what is normally expected in a population or area.
44
What is a pandemic?
An epidemic that spreads across multiple countries or continents.
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What is epidemiology?
The study of how diseases occur and spread in populations.
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What is incidence?
The number of new cases in a population or area during a specified period.
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What is prevalence?
The total number of existing cases in a population or area at a given time or during a specified period.
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What is morbidity?
The proportion or frequency of people in a population who are ill.
49
What is mortality?
The frequency or proportion of deaths in a population due to a disease.
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How can a disease have high morbidity but low mortality?
Many people may become ill while few die, as with the common cold.
51
How can geographic mapping help epidemiologists?
It can reveal clusters of cases and help identify possible sources or patterns of disease spread.
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