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Lecture 7: Infection and Disease


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Whether or not someone is infected vs. diseased depends on what?
The relationship between the host and the parasite.
Infection is the ____ or _____ of the body by pathogenic organisms. Who's winning? THe host or the parasite?
invasion or colonization of the body by pathogenic organisms. You're winning.
DISEASE is any deviation from? Who's winning?
the normal healthy state of an organism. Pathogen is winning.
A person may be ______ but show no symptoms of ____.
What is normal flora?
normal flora are microorganisms that infect the body without causing disease.
Name three places were normal flora can be found.
THe intestines have normal flora that aid in _____ and synthesis of ____.
vitamin K
Give examples of the normal flora that exist in intestines.
E. coli
Enterobacter, Proteus, Klebsiella, Candida albicans (microorganisms determined by diet)
The skin is covered with tons (_#__) of microorganims. What organism can be found on the skin?

What microorganism produces acid through fermentation?
Staphylococci, found on the skin, produces acid through fermentation. It helps prevent _____ pathogens from ___
Give an example of a normal flora found on the vagina?
What does lactobacillus feed on?
glycogen produced by vaginal epithelium
Lactobacillus feeds on glycogen produced by vaginal epithelium. The ___ produced inhibits other microorganisms.
What are the five steps in the progress of disease?
1) Incubation period
2) prodromal
3) Acme
4) Defervescence
5) Convalescence
Incubation period
timebetween entry of parasite and appearance of symptoms
host-pathogen battle time.

mild signs or symptoms. This period is characterized by general symptoms such as nausea, fever, headahce, and MALAISE, which indicate that the competition for surpremacy has begun.
acute stage of disease (specific symptoms appear).

If pathogen wins, go from prodromal to acme.
symptoms fade. period of decline.
body's systems return to normal
What is the #1 killer in the world?
Acute respiratory diseases: 3.9 million
Name some of the most prolific killers in the world.
- Acute respiratory diseases
- tropical diseases
- malaria
- childhood diseases
- diarrheal diseases
- tuberculosis
- other infectious diseases
pathogenicity is the ability of a parasite to enter host tissues and cause disease by effecting ____ or ____ change, resulting in altered health and leading to disease
the ability of a parasite to enter host tissues and cause disease by effecting physiological or anatomical change, resulting in altered health and leading to disease
the degree of pathogenicity of a parasite
Very pathogenic or really virulent microbes cause serious diseases. Give two microbes that are "highly virulent."
Vibrio cholerae (cholera)
Salmonella typhi (typhoid fever)
Less pathogenic or moderately virulent cause less serious diseases. Give an example of a moderately virulent microbe.
Rhinoviruses (common cold)
What kind of microbes do not cause disease?
Avvirulent microbes do not cause disease. They are not pathogenic. MOst organisms have the potential to mutate and become ____
_____ microbes only cause disease when host is compromised
Opportunistic microbes only cause disease when the host is compromised. THey prey on the weak. Give two examples of compromised hosts.
HIV/AIDS patients compromised
Young children & babies
HIV/AIDS patients are compromised and more susceptible to which two opportunistic microbes?
- Pneumocystis jiroveci
- Toxoplasma gondii (cats carry this)
Diseases can be transmitted by either direct or indirect methods. Give 3 direct methods.
- Close personal contact (contact w/ animals)
- Exchange of bodily fluids
- Direct exposure to airborne droplets(by respiratory droplets)
Give 3 indirect methods for transmission of disease.
- Ingesting contaminated food/water
- contact w/ fomites (inanimate objects that carry disease organisms. ex: fork, waterbottle)
- Arthropods (flies, mosquitoes)
what are fomites?
inanimate objects that carry disease organisms. ex: fork, waterbottle
Living organims that carry disease agents from one host to another, such as arthropods, are called vectors. What are the two vectors?
Mechanical vector (disease on legs of arthropod)

Biological vector (insect is infected)
Mechanical vector
arthropod passively transports microorganisms on its legs and other body parts.
biological vector
arthropod itself is diseased
For a disease to keep going there must be a continuing source of disease microorganisms in nature. This continuing source of disease microorganisms is called a ____
A reservoir could be a ___, an ____, or a _____

ex: cats w/ toxoplasmosis
A ___ is a special type of reservoir
Generally, a carrier is one who has ____ from the disease but _____.
continues to shed the disease agents
Give an example of a carrier, a special type of reservoir.
Typhoid Mary
She didn't know she carried typhoid fever. was a cook. whole family that she served got it.

- ppl who have recovered from typhoid fever become carriers for many weeks after the symptoms of disease have left. Their feces may spread the disease to others via contaminated food or water.
What is the field of science that evaluates origin, cause, spread, and control of disease?
endemic disease
steady frequency of a disease in a particular area

An endemic disease is one that occurs at a low level in a certain geographic area.
epidemic disease
sudden, high incidence of a disease. outbreak is a contained epidemic.

An epidemic disease breaks out in explosive proportions within a population. Influenza often causes epidemics. This should be contrasted with an outbreak, which is a more contained epidemic. An abnormally high # of measles cases in one US city would be classified as an outbreak.
Pandemic dsease
world epidemic. ex: AIDS
measure of those who GET a particular disease.

total # of ill people/total # of people
What is the fraction for morbidity?
total # of ill people/total # of people
measure of those who DIE from a particular disease

total # of deaths/ # of ill ppl
Describe chickenpox in terms of morbidity and mortality
chicken pox: high morbidity, low mortality
Describe AIDS in terms of morbidity and mortality.
AIDS: low morbidity, high mortality
What is the difference between morbidity and mortality?
morbidity= get a disease
mortality= die from a disease
Establishment of disease. What is different with each sisease?
portal of entry
Tetanus occurs only when anaerobic ____ is introduced into a deep puncture wound.
Clostridium tetani
Why don't ingested spores cause disease?
stomach nis not a portal of entry. For example, it needs to be a deep puncture wound for tetanus to occur. But even if microbe finds right portal, proliferation may take time.
What are the five steps to establishment of disease?
An infectious dose of microorganisms penetrates the host's defensive barrier. need a certain # of organisms to cause disease.
microorganisms enter the sterile environment of the host's tissues through portal of entry.
microorganisms move into a specific target tissue, such as an organ.
after moving into an organ, they cause tissue damage, leading to disease
microorganisms leave the host through a portal of exit to infect another host.
Name two factors that establish a disease
tissue penetration
dose is the # of ______ to establish disease
parasites needed
dose is the number of parasites needed to establish disease. A little (few hundred thousand) of _____
Mycobacterium tuberculosis
dose is the number of paraistes needed to establish disease. A lot (millions) of ____
vibrio cholerae
Tissue penetration. Pathogens are more invasive. Genes for cell penetration exist on the chromosome of certain bacteria. These gense appear to code for surface proteins that assist penetration. Pathogens use their invasive tendencies to gain access to pr
E. coli O157:H7
E. coli
There are other mechanisms that tissue penetration. ______ remains on the surface and makes _____.
Bordetella pertussis


Bordetella pertussis forms pseudomembrane, blocks airway, produces whooping cough
Adhesion allows ____ of pathogens on the right tissue
Adhesion is mediated by proteins called ___.
adhesins are ___, which are usually found on: ____, ____, ____

- outer surface of bacterial cell wall or mycoplasma membrane (M protein of Streptococcus)
- fimbrae or pili
- flagella
Give an example of an adhesin that is found on the outer surface of a bacterial cell wall or mycoplasma membrane
M protein of Streptococcus
What are two methods that allow for cell internalization, the ability to be taken up by host cell?
- Phagocytic host cells (bacteria gets eaten)

- Bacterial-induced endocytosis (pathogen goes to human host, which will think its food, internalize it through endocytosis)
Cell-to-Cell Transport. What two organisms can use the host cell's actin for cell-to-cell invasion?
Listeria and Shigella use host cell's actin to move through host cytoplasm. These pathogens synthesize an ___ that propels the organism through the cell's cytoplasm.
actin tail
How do the listeria and shigella that form actin tails get to the next host?
Cadherin bridge junction
Cell-to-cell transport allows bacterial invasion to occur without the bacteria ____.
leaving the cellular environment.

Bacterial invasion in the comfort of infected host cell.

avoid immune system.
virulence, or _______, encode proteins involved in penetration, adhesion, internalization, or cell-to-cell transport.
pathogenicity genes
Virulence or pathogenicity genes encode protiens involved in ____, ____, _____, or _____.
cell-to-cell transport
What's the term for genes that are clustered in a pathogen's chromosome?
pathogenicity islands
Pathogenicity islands
genes are clustered in pathogen's chromosome. The cluster of genes responsible for virulence. These blocs of genetic information could move from a pathogenic strain into an avirulent organism, converting it to a pathogen.
Expression of genes takes place only if?
there are a sufficient number of pathogens present
What is quorum sensing?
Turning on virulence factor only if enough "buddies" (pathogens) around. can sense buddies by chemical messenger.
What is the mechanism of quorum sensing?
pathogens secrete homoserine lactone (messenger)
What do the pathogens in quorum sensing secrete as a messenger?
homoserine lactone
What happens when there is a lot of homoserine lactone secreted?
When critical level of homoserine lactone is high enough, corresponding to having enough pathogens), virulence genes are expressed.
The virulence of a parasite depends to some degree on its ability to produce a series of extracellular _____ that hep the pathogen resist body defenses.

The enzymes act on host cells and interfere with certain functions or barriers meant to retard invasion.
What is the source of coagulase?
What is the action and effect of caogulase?
action: forms a fibrin clot
effect: allows resistance to phagocytosis
What is the source of streptokinase?
What is the action and effect of streptokinase?
action: dissolves a fibrin clot.

effect: prevents isolation of infection
What is the source of hyaluronidase?
What is the action and effect of Hyaluronidase?
action: digests hyaluronic acid

effect: allows tissue penetration
What is the source of leukocidin?
Certain rods
What is the action and effect of leukocidin?
action: disintegrates phagocytes

effect: limits phagocytosis
What is the source of hemolysins?
What is the action and effect of hemolysins?
action: dissolves red blood cells

effect: induces anemia and limits oxygen delivery
Pathogenicity can also depend on ____ or ____ produced by pathogenic microorganisms.
poisons or toxins
EXOTOXINS. Proteins from Gram-______ bacteria released into environment--gets into ______ and _____.

blood and cirulation

*Exotoxins are target-cell specific- neurotoxin, enterotoxin
ENDOTOXINS. Gram-_____ cell wall component that is relased upon disintegration of bacteria. Lipid of ____ of the outermembrane is the endotoxin.

LPS (lipopolysaccharide)
Location in bacterium?
Chemical composition?



Antibodies elicited?
Conversion to toxoid?
Liberation of toxin?


On production by the cell

Representative effects?
Interfere with synaptic activity
Interrupt protein synthesis
Increase capillary permeability
Increase water elimination
Location in bacterium?
Chemical composition?
Gram-negative bacteria
Cell wall
Antibodies elicited?
Conversion to toxoid?
Liberation of toxin?
Not possible
On disintegration of the cell
Representative effects?
Increase body temperature
Increase hemorrhaging
Increase swelling in tissues
Induce vomiting, diarrhea

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