CHAPTER 14: PATHOGENESIS OF INFECTIOUS DISEASES

microbes

are too small to be seen with the unaided eye.

disease

The prefix path- comes from the Greek word “pathos,” meaning _____________.

path-, patho-

Words containing the prefix “________” or “_______” pertain to disease.

pathogen

pathology

pathologist

pathogenicity

pathogenesis

Examples of words containing this prefix are

______________ (a microbe capable of causing disease),

______________ (the study of the structural and functional manifestations of disease),

____________ (a physician who has specialized in pathology),

____________ (the ability to cause disease), and

________________ (the steps or mechanisms involved in the development of a

disease).

infectious disease

pathogens

________________ is a disease caused by a microbe, and the microbes that cause xxxxxxx are collectively referred to as _____________.

synonyms

In general usage, the terms infection and infectious disease are _____________.

infection

infectious disease

Many microbiologists, however, reserve use of the word ____________ to mean colonization by a pathogen

it is possible for a person to be infected with a certain pathogen, but not have the _______________ caused by that pathogen

immune, nutritional, and overall health status.

Many factors influence whether or not exposure to a pathogen results in disease, including a person’s _______________, _______________, and _______________.

unable to multiply

specific receptor sites

Antibacterial factors

microbial antagonism

bacteriocins

nutritional and overall health status

immune, vaccinated

Phagocytic white blood cells (phagocytes)

Many people who are exposed to pathogens do not get sick. Listed here are some possible explanations:

• The microbe may land at an anatomic site where it is __________________.

• Many pathogens must attach to _____________________ before they are able to multiply and cause damage. If they land at a site where such receptors are absent, they are unable to cause disease.

• _______________ that destroy or inhibit the growth of bacteria (e.g., the lysozyme that is present in tears, saliva, and perspiration) may be present at the site where a pathogen lands.

• The indigenous microflora of that site (e.g., mouth, vagina, intestine) may inhibit growth of the foreign microbe by occupying space and using up available nutrients. This is a type of ________________, which one microbe or group of microbes wards off another.

• The indigenous microflora at the site may produce antibacterial factors (proteins called ___________) that destroy the newly arrived pathogen. This is also a type of microbial antagonism.

• The individual’s _____________________ often influences the outcome of the pathogen–host encounter. A person who is in good health, with no underlying medical problems, would be less likely to become infected than a person who is malnourished or in poor health.

• The person may be __________ to that particular pathogen, perhaps as a result of prior infection with that pathogen or having been _________ against that pathogen.

• _____________________ (_________) present in the blood and other tissues may engulf and destroy the pathogen before it has an opportunity to multiply, invade, and cause disease.

incubation period

prodromal period

period of illness

convalescent period

The four periods or phases of an infectious disease are the

(a) ___________________,

(b) __________________,

(c) _______________, and

(d) _______________.

incubation period

The ______________________ is the time that elapses between arrival of the pathogen and the onset of symptoms. The length of the incubation period

is influenced by many factors, including the overall health and nutritional status of the host, the immune status of the host (i.e., whether the host is immunocompetent or immunosuppressed), the virulence of the pathogen, and the number of pathogens that enter the body.

prodromal period

The __________________ is the time during which the patient feels “out of sorts” but is not yet experiencing actual symptoms of the disease. Patients may feel like they are “coming down with something” but are not yet sure what it is.

period of illness

Communicable diseases

The ____________________ is the time during which the patient experiences the typical symptoms associated with that particular disease (e.g., sore throat,

headache, sinus congestion). ____________________ are most easily transmitted during this third period.

convalescent period

encephalitis or meningitis

poliomyelitis

deafness

The _________________ is the time during which the patient recovers. For certain infectious diseases, especially viral respiratory diseases, the xxxxxxx can be quite long. Although the patient may recover from the illness itself, permanent damage may be caused by destruction of tissues in the affected area. For example, brain damage may follow _______________ or ________________, paralysis may follow ______________, and _____________ may follow ear infections.

1. Exposure to pathogen

2. Incubation period

3. Prodomal period

4. Period of illness

5. Convalescence

6. Disability

7. Death

Periods in the course of an infectious disease.

localized infections

Once an infectious process is initiated, the disease may remain localized to one site or it may spread. Pimples, boils, and abscesses are examples of

_______________________.

systemic infection, generalized infection

miliary (disseminated) tuberculosis

If the pathogens are not contained at the original site of infection, they may be carried to other parts of the body by way of lymph, blood, or, in some cases, phagocytes. When the infection has spread throughout the body, it is referred to as either a ________________ or a ____________________.

For example, the bacterium that causes tuberculosis—

Mycobacterium tuberculosis—may spread to many

internal organs, a condition known as ___________________.

localized

systemic or generalized infection

An infection may remain ____________ or it may spread, becoming a _____________.

acute disease

An _________________ has a rapid onset, usually followed by a relatively rapid

recovery; measles, mumps, and influenza are examples.

chronic disease

A ______________ has an insidious (slow) onset and lasts a long time; examples are tuberculosis, leprosy (Hansen disease), and syphilis.

subacute diseases

subacute bacterial endocarditis

Some diseases, such as bacterial endocarditis, come on more suddenly than a chronic disease, but less suddenly than an acute disease; they are referred to as ________________. An example of a XXXXXX is _____________________, often referred to merely as SBE.

acute, subacute, or chronic

A disease may be _____________, _____________, or _________, depending on the length of its incubation period and duration.

symptom of a disease

is defined as some evidence of a disease that is experienced

or perceived by the patient; something that is subjective.

any type of ache or pain, a ringing in the ears (tinnitus), blurred vision, nausea, dizziness, itching, and chills.

symptomatic, asymptomatic

Diseases, including infectious diseases, may be either ____________or _________________.

symptomatic disease

clinical disease

A ___________________ (or _________________) is a disease in which the patient is experiencing symptoms.

asymptomatic disease

subclinical disease

An _____________________ (or _______________) is a disease that the patient is unaware of because he or she is not experiencing any symptoms.

Symptoms of a disease

are subjective, in that they are perceived by the patient.

symptomatic, asymptomatic

symptomatic, asymptomatic

In its early stages, gonorrhea (caused by the bacterium,

Neisseria gonorrhoeae) is usually ___________________ in male patients

(who develop a urethral discharge and experience

pain while urinating), but ________________ in female patients.

Only after several months, during which the organism may

have caused extensive damage to her reproductive organs,

is pain experienced by the infected woman.

In trichomoniasis

(caused by the protozoan, Trichomonas vaginalis), the

situation is reversed. Infected women are usually _________________________

(experiencing vaginitis), whereas infected men are usually

__________________. These two sexually transmitted diseases

are especially difficult to control because people are often

unaware that they are infected and unknowingly transmit

the pathogens to others during sexual activities.

sign of a disease

A __________________ is

defined as some type of objective

evidence of a disease.

while palpating a

patient, a physician might discover

a lump or an enlarged

liver (hepatomegaly) or spleen

(splenomegaly).

abnormal

heart or breath sounds, blood pressure, pulse rate, and laboratory

results as well as abnormalities that appear on radiographs,

ultrasound studies, or computed tomography

(CT) scans.

Signs of a disease

are

objective findings,

such as laboratory test

results, which are not

perceived by the

patient.

latent infections

An infectious disease may go

from being symptomatic to

asymptomatic and then, some

time later, go back to being

symptomatic. Such diseases

are referred to as ____________________

latent infections

from the Greek

word “latens,” meaning to lie hidden.

Herpes virus infections,

such as cold sores (fever blisters), genital herpes

infections, and shingles

Cold sores

occur intermittently, but the

patient continues to harbor the herpes virus between

cold sore episodes

Cold sore caused by herpes simplex

trigger

The virus remains dormant

within cells of the nervous system until some type

of stress acts as a _______________.

may be a

fever, sunburn, extreme cold, or emotional stress.

chickenpox

Shingles

A

person who had ________________ as a child may harbor the

virus throughout his or her lifetime and then, later in

life, as the immune system weakens, that person may

develop XXXXXX.

________________, a painful infection of

the nerves, is considered a latent manifestation of

chickenpox.

latent disease

A _________________is a

disease that is lying

dormant, not currently

manifesting itself.

syphilis

If not successfully treated,

_________________ progresses through

primary, secondary, latent,

and tertiary stages

1. Primary Syphilis

2. Secondary Syphilis

3. Latent Syphilis

4. Tertiary Syphilis

Stages of syphilis

primary stage, chancre, Treponema pallidum

Four to six weeks, secondary stage

latent stage

tertiary syphilis

SYPHILIS

During the _______________, the patient has an open lesion called a _____________, which contains the spirochete _________________________

____________________ after the spirochete enters the bloodstream, the chancre disappears, and the symptoms of the _____________ arise, including rash, fever, and mucous membrane lesions.

These symptoms disappear within weeks to 12 months, and the disease enters a ______________, which may last for weeks to years (sometimes

for a lifetime). During the XXXXXXXXXX, the patient has few or no symptoms.

In ________________, the spirochetes cause destruction of the organs in which they have been hiding—the brain, heart, and bone tissue—sometimes

leading to death.

Syphilis chancre on penile shaft.

primary infection

secondary infection

One infectious disease may

commonly follow another, in

which case the first disease is

referred to as a ________________ and the second disease is

referred to as a __________________.

one, different

A primary infection

caused by ________

pathogen can be

followed by a

secondary infection

caused by a _________

pathogen.

primary infection

secondary infection

During the primary infection,

the virus causes damage to the ciliated epithelial

cells that line the respiratory tract. The function of these

cells is to move foreign materials up and out of the respiratory

tract and into the throat where they can be swallowed.

While coughing, the patient may inhale some

saliva, containing an opportunistic bacterial pathogen,

such as Streptococcus pneumoniae or Haemophilus influenzae.

Because the ciliated epithelial cells were damaged by the

virus, they are unable to clear the bacteria from the lungs.

The bacteria then multiply and cause pneumonia.

In this example, the viral infection is the ________________ and

bacterial pneumonia is the ______________________.

entry

attachment

multiplication

invasion

evasion of host defenses

damage to host tissues

An infection may

follow the sequence of

1. Entry of the pathogen into the body

2. Attachment of the pathogen to some tissue(s) within the body

3. Multiplication of the pathogen

4. Invasion or spread of the pathogen

5. Evasion of host defenses

6. Damage to host tissue(s)

Steps in the pathogenesis of infectious diseases.

Entry

__________ of the pathogen into

the body. Portals of entry

include penetration of skin

or mucous membranes by

the pathogen, inoculation of the pathogen into bodily

tissues by an arthropod, inhalation (into the respiratory

tract), ingestion (into the gastrointestinal tract),

introduction of the pathogen into the genitourinary

tract, or introduction of the pathogen directly into the

blood (e.g., through blood transfusion or the use of

shared needles by intravenous drug abusers).

Attachment

Second step in pathogenesis

____________ of the pathogen to some tissue(s) within

the body.

Multiplication

_________________of the pathogen. The pathogen may

multiply in one location of the body, resulting in a localized

infection (e.g., abscess), or it may multiply

throughout the body (a systemic infection).

Invasion or spread

Evasion of host defenses.

Damage to host tissue(s).

4. ___________________ of the pathogen.

5. ______________________

6. ______________________ The damage may be so

extensive as to cause the death of the patient.

not all

It is important to understand that ____________ infectious

diseases involve all these steps in pathogenesis. For example, once ingested,

some exotoxin-producing intestinal pathogens

are capable of causing disease without adhering to the intestinal

wall or invading tissue.

Virulent strains

avirulent strains

_______________________of a

microbe are capable of

causing disease,

whereas _______________ are not.

pathogenic

nonpathogenic

there may be virulent (_______________)

strains and avirulent (_____________) strains of a

particular species.

virulent strains

avirulent strains

The _____________________ are capable of causing disease, whereas the _______________ are not.

virulence

is used

to express a measure or degree

of pathogenicity.

shigellosis

salmonellosis

Shigella

Salmonella

In bacterial diarrhea,

for example, it only takes about 10 Shigella cells to

cause ______________, but it takes between 100 and 1,000

Salmonella cells to cause _______________. Thus, ____________ is

considered to be more virulent than ________________.

erythrogenic toxin

only certain strains of S. pyogenes

produce ___________________ (the cause of scarlet fever);

these strains are considered more virulent than the strains

of S. pyogenes that do not produce XXXXXX.

virulence

is used in reference to the severity

of the infectious diseases that are caused by the

pathogens. Used in this manner, one pathogen is more

virulent than another if it causes a more serious disease.

virulence factors

The physical attributes or properties

of pathogens that enable

them to escape various host defense

mechanisms and cause

disease are called ________________.

Virulence factors

are

phenotypic

characteristics that

enable microbes to be

virulent (to cause

disease).

to attach

Perhaps you have noticed that certain pathogens infect

dogs but not humans, whereas others infect humans but

not dogs. Perhaps you have wondered why certain

pathogens cause respiratory infections whereas others

cause gastrointestinal infections. Part of the explanation

has to do with the type or types of cells to which the

pathogen is able ________________.

To cause disease, some

pathogens must be able to anchor themselves to cells

after they have gained access to the body.

1. pili

2. capsule

3. endotoxin

4. neurotoxins, enterotoxins, and cytotoxins

5. coagulase

6. hemolysins

7. collagenase

8. kinase

9. hyaluronidase

10. leukocidin

11. flagellum

Virulence factors.

receptor and integrin

The general terms ______________________ are used to describe the

molecule on the surface of a

host cell that a particular

pathogen is able to recognize

and attach to

receptors

are glycoprotein

molecules. A particular pathogen can only attach

to cells bearing the appropriate ________________. Thus, certain

viruses cause respiratory infections because they are

able to recognize and attach to certain ______________that are

present on cells that line the respiratory tract.

receptors or integrins.

Molecules on a host

cell’s surface that

pathogens are able to

recognize and attach

to are called

Adhesins and receptors

Bacterial Fimbriae (Pili)

ATTACHMENT

1. virus

2. host cell

3. adhesin (ligand)

4. receptor (integrin)

Adhesins and receptors

fibronectin

S. pyogenes cells have an adhesin (called protein F) on

their surfaces that enables this pathogen to adhere to a

protein—_____________—that is found on many host cell

surfaces.

CD4

CD4 cells

T-helper cells

Human immunodeficiency virus (HIV; the virus

that causes acquired immunodeficiency syndrome [AIDS])

is able to attach to cells bearing a surface receptor called

____________. Such cells are known as _____________. A category of

lymphocytes called ___________________ (the primary target cells

for HIV) are examples

adhesins or ligands

Molecules on a

pathogen’s surface that

recognize and attach

to receptors on a host

cell’s surface are called

______________________.

antibodies

directed against such adhesins prevent the pathogen from

attaching and, thus, prevent infection by that pathogen.

are proteins that our immune systems produce to protect us from pathogens and infectious diseases.

Bacterial fimbriae (pili)

pilin

___________________ are long, thin, hairlike, flexible

projections composed primarily of an array of proteins

called ___________

Fimbriae

considered to be virulence factors because they enable bacteria to attach to surfaces, including various tissues within the human body.

N. gonorrhoeae

Fimbriated (piliated) strains of _____________ are able to anchor themselves to the inner walls of the urethra and cause urethritis.

Escherichia coli

fimbriated strains of _______________ that

gain access to the urinary bladder are able to anchor

themselves to the inner walls of the bladder and cause

cystitis

M-protein

The fimbriae of group A, beta-hemolytic streptococci

(S. pyogenes) contain molecules of _____________.

It serves as a virulence factor in two ways: (a) it

enables the bacteria to adhere to pharyngeal cells; and

(b) it protects the cells from being phagocytized by

white blood cells (i.e., the XXXXXXXX serves an antiphagocytic

function).

colonization factors

bacterial

fimbriae enable bacteria to colonize surfaces, they are

sometimes referred to as

Bacterial fimbriae (pili)

are virulence factors,

in that they enable

fimbriated (piliated)

bacteria to adhere to

cells and tissues within

the human body.

obligate intracellular pathogens

obligate intracellular parasites

Certain pathogens, such as

Gram-negative bacteria in the

genera Rickettsia and Chlamydia

must live within host cells to

survive and multiply; they are referred to as ___________________________(or _______________________).

Rickettsias

invade and live within endothelial cells

and vascular smooth muscle cells.

are capable

of synthesizing proteins, nucleic acids, and adenosine

triphosphate (ATP), but are thought to require an intracellular

environment because they possess an unusual

membrane transport system;

they are said to have leaky

membranes.

chlamydias

The different species and serotypes of __________________

invade different types of cells, including conjunctival epithelial

cells and cells of the respiratory and genital tracts.

produce ATP molecules, they preferentially

use ATP molecules produced by host cells; this

has earned them the title of “energy parasites.”

obligate intracellular pathogens

are propagated

using cell cultures, laboratory animals, or embryonated

chicken eggs.

Rickettsias and chlamydias

are obligate

intracellular pathogens.

intraleukocytic pathogens.

Ehrlichia spp. and Anaplasma

phagocytophilum are Gramnegative

bacteria that closely resemble

Rickettsia spp. They are

______________________________

human monocytic ehrlichiosis (HME)

Ehrlichia spp. live within monocytes,

causing a disease known

as ________________________.

human anaplasmosis

A. phagocytophilum

lives within granulocytes, causing a condition known as

________________ (formerly called human granulocytic

ehrlichiosis or HGE).

intraerythrocytic

pathogens

Certain sporozoan protozoa, such as

the Plasmodium spp. that cause human malaria and the

Babesia spp. that cause human babesiosis, are ________________ (i.e., they live within erythrocytes).

Ehrlichia and Anaplasma spp.

Plasmodium and Babesia spp.

__________________________ are

intraleukocytic

pathogens, whereas

___________________ are

intraerythrocytic

pathogens.

facultative intracellular pathogens.

Pathogens that can

live both within and

outside of host cells

are called _______________________

facultative intracellular pathogens

Many that can be grown in the laboratory

on artificial culture media are also able to survive

within phagocytes.

macrophages and neutrophils

The two most

important categories

of phagocytes in the

human body—referred

to as “professional

phagocytes”—are

____________________.

1. Viruses

2. Rickettsias

3. Other bacteria

4. Protozoa

5. Fungi

Pathogens that Routinely Multiply within Macrophages

phagocytes

play an important

role in our defenses against

pathogens.

M. tuberculosis

Many bacteria,

including

__________________, are

facultative intracellular

pathogens.

Mycobacterial cell walls

___________ contain waxes, and it is

thought that these waxes protect

the organisms from digestion.

Toxoplasma gondii

prevent the fusion of lysosomes

(vesicles that contain digestive enzymes) with the

phagocytic vacuole (phagosome).

Rickettsia rickettsii

produce phospholipases

that destroy the phagosome membrane, thus preventing

lysosome-phagosome fusion.

Bacterial capsules

serve

an antiphagocytic

function (i.e., they

protect encapsulated

bacteria from being

phagocytized).

encapsulated bacteria

Nonencapsulated bacteria

Phagocytes are unable to attach to

____________________________ because they lack surface receptors

for the polysaccharide material of which the capsule is

made.

gain access to the bloodstream or tissues are protected from

phagocytosis, they are able to multiply, invade, and

cause disease.

______________________, on the other

hand, are phagocytized and killed.

Flagella

are considered

to be virulence factors

because they enable

flagellated bacteria

to invade areas

of the body that

nonflagellated bacteria

cannot reach.