Diptheria host and pathogens with cause.ppt

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
© 2012 Pearson Education, Inc.

Figure 33.1

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

Figure 33.3

Figure 33.4

Figure 33.5

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)

Figure 33.6

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

Figure 33.7a

• 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

Figure 33.7b

• 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

• 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

Figure 33.8
Year
1977 1982 1987 1992 1997 2002 2007
9
8
7
6
5
4
3
2
1
0
Pertussis
(incidence
per
100,000
population)

• 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

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

Figure 33.9

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)

Figure 33.10

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

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

Figure 33.12

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

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)

• 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

Figure 33.14

• 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

• Mumps
– Caused by a paramyxovirus (like measles)
– Highly infectious
– Spread by airborne droplets
– Characterized by inflammation of the salivary
glands

Figure 33.16

• 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.

• In the U.S., the incidence of measles, mumps,
and rubella has decreased significantly since
the implementation of the MMR vaccine

Figure 33.15
Measles
Mumps
Rubella
1987 1992 1997 2002 2007 2012
19651970197519801985
400
200
0
1987 1992 1997 2002 2007 2012
19651970197519801985
1987 1992 1997 2002 2007 2012
19651970197519801985
1960
150
100
50
0
0
10
20
30
25
20
15
10
5
0
5
6
7
4
3
2
1
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Cases
per
100,000
population
Cases
per
100,000
population
Cases
per
100,000
population
Vaccine
licensed

• 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.

Figure 33.17

• 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)

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

Figure 33.18
Cases per 100 people per year
All other infectious diseases
Colds
Influenza
400
300
200
100
0

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

Figure 33.19

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

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

Figure 33.21
HA trimer
Lipid bilayer
M protein
NA tetramer
RNA
NP
PA, PB1, PB2

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

Figure 33.22
Reassortant
virus
Human
virus
Bird
virus
Infection
with
bird virus
Reassortment
of human and
bird virus
Infection with
human virus
Infection
with
reassortant
virus

33.8 Influenza
• Influenza epidemics and pandemics occur
periodically
– 1957 outbreak of Asian flu
– 1997 outbreak of avian influenza

Figure 33.23
Country of origin
Countrywide epidemic
Localized outbreaks
Routes of spread

33.8 Influenza
• Prevention
– Immunization
– Careful worldwide surveillance
• Treatment
– Use of various drugs
– Most effective when administered early
– Aspirin should be avoided

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

• 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

Figure 33.27

• Hepatitis C virus
– Produces a mild disease initially, but most
individuals develop chronic hepatitis that can lead
to chronic liver disease

• 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

Figure 33.26
Hepatitis A
Hepatitis B
Hepatitis C
HAV vaccine
1995
HBV vaccine
1982
Year
Cases
per
100,000
population
20
15
10
5
0
1975 1980 1985 1990 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

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

Figure 33.28
Year
Birth control pills
Penicillin
World War II
Reported
cases
per
100,000
population
Syphilis
Gonorrhea
500
400
300
200
100
0
1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

• 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

Figure 33.29

• 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

Figure 33.30

33.13 Chlamydia, Herpes, and HPV
• Chlamydia trachomatis causes a number of
sexually transmitted diseases
– Nongonococcal urethritis (NGU)
– Lymphogranuloma venereum

Figure 33.32

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

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

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

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

• HIV is divided into two types:
– HIV-1 is the more virulent type
– HIV-2 is less virulent and causes a milder, AIDS-
like disease
• Opportunistic infections are common in AIDS
patients

• A frequent nonmicrobial disease in AIDS
patients is Kaposi’s sarcoma, an atypical
cancer

Figure 33.37

• 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

Figure 33.38
Mature
form
Budding
particles

Figure 33.39
Nucleocapsid
Nucleus
gp 120
CCR5
CD4
Target
cell
Interaction of HIV with a
host cell
Fusion of the HIV envelope with the host cell
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
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

Figure 33.40
Symptom-
free
Swollen lymph glands Subclinical immune
dysfunction
Oppor-
tunistic
infections
Systemic
immune
deficiency
Time (months) after HIV exposure
HIV
RNA
copies
per
ml
Death
CD4
T cells
per
mm3 of
blood
Normal
range
for T cells
Significantly
depressed
T cells
Severe
T cell
depletion
106
104
102
1000
900
800
700
600
500
400
300
200
100
0
0 6 12 18 24 30 36 42 48 54 60 66 72 78 84

• 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

• 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

• There is not an effective vaccine for HIV
• Prevention for the spread of HIV infection
requires education and avoidance of high-risk
behavior

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