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33.1 Airborne Pathogens
• Aerosols are important for person-to-person
transmission of many infectious diseases
• Most pathogens survive poorly in air, thus, are
effectively transmitted only over short distances
• Respiratory infections
– Different pathogens characteristically colonize the
respiratory tract at different levels
– The upper and lower respiratory tracts offer
different environments and favor different
microbes
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Figure 33.1
© 2012 Pearson Education, Inc.
33.2 Streptococcal Diseases
• Streptococcus pyogenes (group A Streptococcus;
GAS)
– Commonly found in low numbers in the upper
respiratory tract of healthy individuals
– Causative agent of “strep throat”
– Can also cause infections of the inner ear,
mammary glands, and skin
• Infections occur if host defenses are weakened or
a new, highly virulent strain is introduced
© 2012 Pearson Education, Inc.
Figure 33.3
© 2012 Pearson Education, Inc.
Figure 33.4
© 2012 Pearson Education, Inc.
Figure 33.5
© 2012 Pearson Education, Inc.
33.2 Streptococcal Diseases
• Streptococcus pyogenes (cont’d)
– Certain GAS strains carry a lysogenic
bacteriophage that encodes exotoxins responsible
for symptoms of toxic shock syndrome and scarlet
fever
– Untreated or insufficiently treated infections can
lead to other diseases (e.g., rheumatic fever)
© 2012 Pearson Education, Inc.
Figure 33.6
© 2012 Pearson Education, Inc.
33.3 Diphtheria and Pertussis
• Diphtheria
– A severe respiratory disease that typically
infects children
– Caused by Corynebacterium diphtheriae
• A bacterium that forms irregular rods during
growth
– Preventable and treatable
© 2012 Pearson Education, Inc.
Figure 33.7a
© 2012 Pearson Education, Inc.
33.3 Diphtheria and Pertussis
• Corynebacterium diphtheriae
– Spreads by airborne droplets and enters the body
via the respiratory route
– Previous infection or immunization provides
resistance
– Pathogenic strains lysogenized by bacteriophage
 produce a powerful exotoxin that causes
• Tissue death
• The appearance of the pseudomembrane in the
patient’s throat
© 2012 Pearson Education, Inc.
Figure 33.7b
© 2012 Pearson Education, Inc.
33.3 Diphtheria and Pertussis
• Diagnosis of Diphtheria
– C. diphtheriae must be isolated from the throat
• Prevention of Diphtheria
– Vaccine
• Treatment of Diphtheria
– Antibiotics
– Diphtheria antitoxin available for acute cases
• Early administration necessary
© 2012 Pearson Education, Inc.
33.3 Diphtheria and Pertussis
• Pertussis (whooping cough)
–
–
–
–
–
An acute, highly infectious respiratory disease
Caused by infection with Bordetella pertussis
Observed frequently in school-age children
Characterized by a recurrent, violent cough
There has been a consistent upward trend of
infections since the 1980s
– Inadequately immunized children, adolescents,
and adults are at high risk for acquiring and
spreading pertussis
© 2012 Pearson Education, Inc.
Figure 33.8
Pertussis (incidence per
100,000 population)
9
8
7
6
5
4
3
2
1
0
1977
1982
1987
1992
Year
© 2012 Pearson Education, Inc.
1997
2002
2007
33.3 Diphtheria and Pertussis
• Diagnosis
– Made by fluorescent antibody staining of a
nasopharyngeal swab specimen
– Also made by actual culture of the organism
• Prevention
– Vaccine soon after birth
• Treatment
– Antibiotics
– But elimination is helped by the immune response
© 2012 Pearson Education, Inc.
33.4 Mycobacterium, Tuberculosis, and
Hansen’s Disease
• Tuberculosis is caused by Mycobacterium
tuberculosis
• Hansen’s disease (leprosy) is caused by
Mycobacterium leprae
• All mycobacteria are acid-fast due to the
waxy mycolic acid content of their cell walls
© 2012 Pearson Education, Inc.
Figure 33.9
© 2012 Pearson Education, Inc.
33.4 Mycobacterium, Tuberculosis, and
Hansen’s Disease
• Tuberculosis
–
–
–
–
Worldwide infectious disease of humans
Incidence is increasing
M. tuberculosis transmitted by airborne droplets
Cell-mediated immunity plays a critical role in
the prevention of active disease after infection
– Classified as a primary (initial) infection or
postprimary infection (reinfection)
© 2012 Pearson Education, Inc.
Figure 33.10
© 2012 Pearson Education, Inc.
33.4 Mycobacterium, Tuberculosis, and
Hansen’s Disease
• Spread of tuberculosis is prevented by
– Hospitalization of patients in negative-pressure
rooms
– Use of face masks for healthcare workers
• Treatment
– Antimicrobial therapy with isoniazid
• Treatment usually requires a 9-month regimen
• Affects the synthesis of mycolic acid in
mycobacteria
© 2012 Pearson Education, Inc.
33.4 Mycobacterium, Tuberculosis, and
Hansen’s Disease
• Hansen’s disease (leprosy)
– M. leprae is the causative agent
– The armadillo is the only experimental animal
that has been successfully used to grow
M. leprae
– Most serious form is characterized by folded,
bulblike lesions on the body
© 2012 Pearson Education, Inc.
Figure 33.12
© 2012 Pearson Education, Inc.
33.4 Mycobacterium, Tuberculosis, and
Hansen’s Disease
• Pathogenicity of M. leprae
– Due to a combination of delayed hypersensitivity
and the invasiveness of the organism
– Transmission is by both direct contact and
respiratory routes
– Incubation times vary from several weeks to years
– The incidence of leprosy worldwide is low
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Viruses are less easily controlled by
chemotherapeutic methods
• The most prevalent human infections are caused
by viruses
• Most viral diseases are acute, self-limiting
infections
• A few serious viral diseases have been effectively
controlled by vaccination (e.g., smallpox and
rabies)
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Measles (rubeola or 7-day measles)
– Often affects susceptible children as an acute,
highly infectious, often epidemic disease
(Figure 33.14)
– Caused by a paramyxovirus
• Negative-strand RNA virus
– Virus enters the nose and throat by airborne
transmission
© 2012 Pearson Education, Inc.
Figure 33.14
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Measles (cont’d)
– Used to be a common childhood illness
– Now only occurs in rather isolated outbreaks
• Due to widespread immunization programs that
began in the mid-1960s
– Over 600,000 deaths per year worldwide
– Proof of immunization required for enrollment in
U.S. public schools
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Mumps
–
–
–
–
Caused by a paramyxovirus (like measles)
Highly infectious
Spread by airborne droplets
Characterized by inflammation of the salivary
glands
© 2012 Pearson Education, Inc.
Figure 33.16
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Rubella (German measles or 3-day measles)
– Caused by a positive-strand RNA virus of the
togavirus group
– Disease symptoms resemble measles but are
generally milder and less contagious
– Routine childhood immunization is practiced in
the U.S.
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• In the U.S., the incidence of measles, mumps,
and rubella has decreased significantly since
the implementation of the MMR vaccine
© 2012 Pearson Education, Inc.
Cases per
100,000 population
Figure 33.15
30
25
20
15
10
5
0
1987
400
Vaccine
licensed
200
0
1965197019751980 1985
1992
1997
2002
2007
2012
Cases per
100,000 population
Measles
7
6
5
4
3
2
1
0
1987
150
100
50
0
19651970197519801985
1992
1997
2002
2007
2012
Cases per
100,000 population
Mumps
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1987
Rubella
© 2012 Pearson Education, Inc.
20
10
0
1960 19651970197519801985
1992
1997
2002
2007
2012
33.6 Viruses and Respiratory Infections
• Chicken pox (varicella)
– Common childhood disease characterized by a
systemic papular rash
– Caused by varicella-zoster virus (VZV), a
herpesvirus
– VZV is highly contagious and transmitted by
infectious droplets
– A vaccine is presently used in the U.S.
© 2012 Pearson Education, Inc.
Figure 33.17
© 2012 Pearson Education, Inc.
33.6 Viruses and Respiratory Infections
• Chicken pox (cont’d)
– VZV virus establishes a lifelong latent
infection in nerve cells
– The virus occasionally migrates to the skin
surface, causing a painful skin eruption
(shingles)
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33.7 Colds
• Colds
– Viral infections transmitted via airborne droplets
– Infections are usually of short duration
– Symptoms milder than other respiratory
diseases
– Symptoms include rhinitis, nasal obstruction,
watery nasal discharges, and malaise
© 2012 Pearson Education, Inc.
Figure 33.18
All other infectious diseases
Colds
Influenza
0
100
200
300
Cases per 100 people per year
© 2012 Pearson Education, Inc.
400
33.7 Colds
• The Common Cold
– Commonly caused by rhinoviruses (Figure 33.19)
• Positive-sense, single-stranded RNA viruses
• Nearly 115 different strains identified
– Approximately 15% of colds are due to
coronaviruses
– Approximately 10% of colds are due to other
viruses
© 2012 Pearson Education, Inc.
Figure 33.19
© 2012 Pearson Education, Inc.
33.7 Colds
• Each cold infection induces a specific,
protective immunity, but the large number of
viral cold pathogens precludes complete
protective immunity or vaccines
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33.8 Influenza
• Influenza is caused by an RNA virus of the
orthomyxovirus group
• There are three different types of influenza
viruses (A, B, C)
• Influenza A is the most important human
pathogen
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Figure 33.21
HA trimer
Lipid bilayer
M protein
NA tetramer
RNA
NP
PA, PB1, PB2
© 2012 Pearson Education, Inc.
33.8 Influenza
• Influenza outbreaks occur annually due to the
plasticity of the influenza genome
– Antigenic shift
• Major change in influenza virus antigen due to
gene reassortment (Figure 33.22)
– Antigenic drift
• Minor change in influenza virus antigens due to
gene mutation
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Figure 33.22
Bird
virus
Reassortant Human
virus
virus
Infection with
human virus
Infection
with
bird virus
Reassortment
of human and
bird virus
© 2012 Pearson Education, Inc.
Infection
with
reassortant
virus
33.8 Influenza
• Influenza epidemics and pandemics occur
periodically
– 1957 outbreak of Asian flu
– 1997 outbreak of avian influenza
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Figure 33.23
Country of origin
Countrywide epidemic
Localized outbreaks
Routes of spread
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33.8 Influenza
• Prevention
– Immunization
– Careful worldwide surveillance
• Treatment
– Use of various drugs
– Most effective when administered early
– Aspirin should be avoided
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33.11 Hepatitis Viruses
• Hepatitis
– Liver inflammation caused by viruses or bacteria
– Sometimes results in acute illness followed by
destruction of liver anatomy and cells (cirrhosis)
– A restricted group of viruses is associated with
liver disease
– Hepatitis viruses are diverse
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33.11 Hepatitis Viruses
• Hepatitis A virus (infectious hepatitis)
– Causes mild or, rarely, severe cases of liver
disease
• Hepatitis B virus (serum hepatitis; Figure 33.27)
– Causes acute, often severe disease that can lead
to liver failure and death
• Hepatitis D virus
– A defective virus that cannot replicate and
express a complete virus unless the cell is also
infected with hepatitis B
© 2012 Pearson Education, Inc.
Figure 33.27
© 2012 Pearson Education, Inc.
33.11 Hepatitis Viruses
• Hepatitis C virus
– Produces a mild disease initially, but most
individuals develop chronic hepatitis that can lead
to chronic liver disease
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33.11 Hepatitis Viruses
• Incidence and Prevalence of Hepatitis
– Decreased significantly in the U.S. in the last
20 years (Figure 33.26)
– Viral hepatitis is still a major public health
problem
• Due to the high infectivity of the viruses and the
lack of effective treatment options
– Vaccines are available for Hepatitis A and B
viruses
© 2012 Pearson Education, Inc.
Figure 33.26
Cases per 100,000
population
20
HBV vaccine
1982
HAV vaccine
1995
Hepatitis A
Hepatitis B
Hepatitis C
15
10
5
0
1975
1980
1985
1990
Year
© 2012 Pearson Education, Inc.
1995
2000
2005
2010
III. Sexually Transmitted Infections
• Sexually Transmitted Infections (STIs)
– Also called sexually transmitted diseases (STDs)
or venereal diseases
– Caused by a variety of bacteria, viruses, protists,
and even fungi
– Pathogens are generally only found in body fluids
from the genitourinary tract that are exchanged
during sexual activity
© 2012 Pearson Education, Inc.
33.12 Gonorrhea and Syphilis
• Gonorrhea and syphilis are preventable,
treatable bacterial STIs
• The overall pattern of disease differs between
the two
– Gonorrhea is prevalent and often
asymptomatic in women
– Syphilis has low prevalence and exhibits very
obvious symptoms
© 2012 Pearson Education, Inc.
Reported cases per 100,000 population
Figure 33.28
500
400
World War II
Birth control pills
Syphilis
300
Gonorrhea
200
100
Penicillin
0
1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
© 2012 Pearson Education, Inc.
Year
33.12 Gonorrhea and Syphilis
• Gonorrhea
– Caused by Neisseria gonorrhoeae
– Symptoms in females
• Characterized by a mild vaginitis that often goes
unnoticed
• Untreated gonorrhea can lead to pelvic
inflammatory disease
– Symptoms in males
• Characterized by a painful infection of the
urethral canal
© 2012 Pearson Education, Inc.
Figure 33.29
© 2012 Pearson Education, Inc.
33.12 Gonorrhea and Syphilis
• Syphilis
– Caused by Treponema pallidum
– Often transmitted at the same time as gonorrhea
– T. pallidum can be transmitted from an infected
woman to the fetus during pregnancy (congenital
syphilis)
– Three stages: primary, secondary, and tertiary
– Penicillin highly effective for primary and
secondary stages
© 2012 Pearson Education, Inc.
Figure 33.30
© 2012 Pearson Education, Inc.
33.13 Chlamydia, Herpes, and HPV
• Chlamydia trachomatis causes a number of
sexually transmitted diseases
– Nongonococcal urethritis (NGU)
– Lymphogranuloma venereum
© 2012 Pearson Education, Inc.
Figure 33.32
© 2012 Pearson Education, Inc.
33.13 Chlamydia, Herpes, Trichomoniasis,
and HPV
• Herpes simplex 1 virus (HSV-1)
– Infects the epithelial cells around the mouth
and lips
– Causes cold sores
– May occasionally affect other body sites
– Spread via direct contact or through saliva
– Lesions heal without treatment in 2 to 3 weeks
© 2012 Pearson Education, Inc.
33.13 Chlamydia, Herpes, Trichomoniasis,
and HPV
• Herpes simplex 2 virus (HSV-2)
– Infections are associated primarily with anogenital
region
– Causes painful blisters on penis of male and cervix,
vulva, or vagina of females
– Typically transmitted through sexual contact and
most easily transmitted when active blisters are
present
– Genital herpes are presently incurable, however, a
limited number of drugs are successful in controlling
the infectious blister stage
© 2012 Pearson Education, Inc.
33.13 Chlamydia, Herpes, Trichomoniasis,
and HPV
• Human papillomavirus (HPV)
– Causes several different infections
• Many infections are asymptomatic but some
progress to genital warts
• Can cause cervical neoplasia, and a few progress
to cervical cancers
– There is an effective HPV vaccine
© 2012 Pearson Education, Inc.
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• AIDS
– Recognized as a distinct disease in 1981
– Human immunodeficiency virus (HIV) is the
causative agent
• HIV
– As many as 1.4 million people worldwide may
be infected
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33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• HIV is divided into two types:
– HIV-1 is the more virulent type
– HIV-2 is less virulent and causes a milder, AIDSlike disease
• Opportunistic infections are common in AIDS
patients
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33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• A frequent nonmicrobial disease in AIDS
patients is Kaposi’s sarcoma, an atypical
cancer
© 2012 Pearson Education, Inc.
Figure 33.37
© 2012 Pearson Education, Inc.
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• HIV Pathogenesis
– HIV infects cells that contain the CD4 cell surface
protein
– Most commonly infected are macrophages and
T-helper cells
– HIV also interacts with coreceptors on target cells
© 2012 Pearson Education, Inc.
Figure 33.38
Mature
form
Budding
particles
© 2012 Pearson Education, Inc.
Figure 33.39
HIV gp120 protein binds CD4
receptor and CCR5 receptor
Interaction of the
virus with a receptor–
coreceptor pair on
the host cell
The viral envelope
and host membrane
coalesce
The nucleocapsid
is inserted into
the host cell,
beginning the
viral infection
Nucleocapsid
HIV
gp 120
CD4
CCR5
Target
cell
Nucleus
Interaction of HIV with a
host cell
© 2012 Pearson Education, Inc.
Fusion of the HIV envelope with the host cell
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• HIV infection does not immediately kill the
host cell
• Infection results in a progressive decline in
CD4 cells
• As the number of CD4 cells declines, cytokine
production falls, leading to reduction of the
immune response
© 2012 Pearson Education, Inc.
Figure 33.40
Subclinical immune
dysfunction
Symptom- Swollen lymph glands
free
1000
Systemic
Opporimmune
tunistic
infections deficiency
106
900
Normal
range
for T cells
Significantly
depressed
T cells
Severe
T cell
depletion
800
700
CD4
T cells 600
per
500
mm3 of
blood 400
104
Death 102
300
200
100
0
0
6
12
18
24
30
36
42
48
54
60
Time (months) after HIV exposure
© 2012 Pearson Education, Inc.
66
72
78
84
HIV
RNA
copies
per
ml
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• HIV infection can be diagnosed with an HIV-EIA,
HIV-immunoblot, or rapid tests
– These fail to detect infection in individuals who
recently acquired the HIV and have not made a
detectable antibody
• RT-PCR can detect HIV RNA directly from blood
and estimate the number of viruses present
– This is useful for early detection and monitoring
the progression of infection
© 2012 Pearson Education, Inc.
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• Treatment
– Four classes of drugs delay the symptoms of
AIDS and prolong the life of those infected with
HIV
•
•
•
•
Nucleoside reverse transcriptase inhibitors
Nonnucleoside reverse transcriptase inhibitors
Protease inhibitors
Fusion inhibitors
– Highly active antiretroviral therapy (HAART) is
used
© 2012 Pearson Education, Inc.
33.14 Acquired Immunodeficiency
Syndrome: AIDS & HIV
• There is not an effective vaccine for HIV
• Prevention for the spread of HIV infection
requires education and avoidance of high-risk
behavior
© 2012 Pearson Education, Inc.