Week 8 Flashcards
Transmission modes?
- Contact
- Vehicle
- Vector
Types of contact?
- Direct contact: Kissing, touching, sex, mother to fetus
- Indirect contact: Fomites
- Droplets: Mucus droplets less than 1 meter (exhaling, sneezing coughing)
Vehicle transmission types (Air, water, food, fluids from body)
- Airborne (Aerosols): Dust or droplet goes father than a meter
- Waterborne
- Foodborne
Vector types (Arthrpods, insects)
- Active transmitter
- Passive transmitter
Aerosols
Major vehicles for person to person transmission of resp diseases
- sneezing
- coughing
- talking
- breathing
How do aerosols spread?
Person to person (direct)
Contaminated objects (indirect)
Microorganisms found in air are derived from:
Soil
water
plants
animals
people
surfaces
other sources
How are airborne pathogens effectively transmitted?
between people over short distances
What pathogens survive well in dust or on fomites?
- Gram positive bacteria: due to thick cells walls
- Waxy layer of mycobacterium cell walls resists drying and promotes pathogen survival
How big are infectious droplets?
About 10um in diameter
What is the speed of a droplet?
100m/s in a violent sneeze
15 to 20m/s during coughing or sneezing
number of bacteria in a single sneeze
10 to the 4 to 10 to the 6
How does air move in the lower respiratory tract?
Moves slowly, and particles stop moving and settle (large particles first then smaller)
Upper respiratory tract infections
acute and non-life threatening
Lower respiratory infections
Often chronic and can be quite serious, especially in elderly or immunocompromised individuals such as bacterial or viral pneumonia
Secondary infection
Death of an elderly person from pneumonia following a severe case of influenza
what are some illnesses transferred by direct contact
strep, cold virus, influenza
Upper resp tract airborne pathogens?
Staphylococcus aureus
Neisseria meningitis
streptococcus pyogenes
corynebacterium diphtheria
common cold
Lower tract pathogens
influenza
TB
immitis
pertussis
strep pneumonia
pneumonia viruses
Burnetil
chamydophila pneumonia
Streptococcal diseases transmitted by:
Airborne droplets
direct contact
Most important human respiratory pathogens:
Streptococcus pyogenes: elongated chains, as do many other species of the genus.
Streptococcys pneumoniae: grow in pairs or short chains
* virulent strains produce an extensive polysaccharide capsule
Types of streptococci infections
Group A
Group B
Group C/G
Group A streptococcus (GAS)
Tends to affect the throat and the skin. (βhemolysis)
Group B streptococcus (GBS)
Can cause illness in people of all ages, though it can be particularly
severe in newborns, most commonly causing sepsis, pneumonia,
and meningitis. (αhemolysis)
Group C and G streptococcus
Most commonly live in animals such as horses and cattle and can
spread to humans through raw milk or contact with these animals.
What is Hemolysin
are lipids and proteins that
cause the lysis of red blood cells and liberate hemoglobin by
disrupting the cell membrane.
Streptococcus pyogenes
The major species in the group A streptococci
* Upper respiratory tract microbe of
healthy adults
* A few serious infections are possible if
host defenses are weakened or a new,
highly virulent strain is encountered.
S pyogenes is the cause of:
streptococcal pharyngitis (strep throat)
* infections of the middle ear (otitis media)
* infection of mammary glands (mastitis)
* infections of the superficial layers of the skin called
impetigo
* streptococcal skin infection called erysipelas
* and other conditions linked to the aftereffects of
streptococcal infections.
Strep throat symptoms
severe sore throat, enlarged tonsils , red spots on the soft palate,
tender cervical lymph nodes, a mild fever, general malaise
Untreated group A streptococcal infections can lead to serious
secondary diseases such as
scarlet fever
* rheumatic fever
* acute glomerulonephritis
* streptococcal toxic shock syndrome
Clinical tools for quickly diagnosing strep throat include
Rapid antigen detection systems that contain antibodies specific for cell
surface proteins of S. pyogenes
* obtaining an actual culture of S. pyogenes from the throat or other
suspected lesion on a blood agar plate.
* results of a throat culture may take up to 48 h to process, and such a
delay in treatment can have adverse effects.
Group A Streptococcal Syndromes
Viral encoded exotoxins are responsible for most of
the symptoms of streptococcal toxic shock syndrome
and scarlet fever.
Toxic shock
esults when the activated T cells
secrete cytokines, which in turn activate large
numbers of macrophages and neutrophils,
causing severe inflammation and tissue
destruction.
Scarlet Fever
signaled by a severe sore throat,
fever, and characteristic rash, is readily treatable
with antibiotics or may be self-limiting.
necrotizing fasciitis
rapid and progressive disease resulting in
extensive destruction of subcutaneous tissue, muscle, and fat: “flesh-
eating bacteria.”
What systemic infections are occasionally caused by Group A?
Cellulitis and necrotizing fascitis
Celulitis
Skin infection in the subcutaneous laters
What functions as superantigens to result in tissue destruction/fatalities?
Virus encoded exotoxins and cel surface M proteins
Impetigo
Infections of the superficial layers of the skin
Erysipelas
Streptococcal skin infections
Untreated or insufficiently treated S. pyogenes
may lead to
other severe conditions 1 to 4 weeks after the onset of infection.
Rheumatic fever is caused by?
rhuematogenic strains of S pyogenes
Rheumatic fever
autoimmune complication due to the cross
reaction of antibodies directed against streptococcus with heart valve
and joint antigens, causing inflammation and tissue destruction.
Acute poststreptococcal glomerulonephritis;
a painful kidney disease.
Acute poststreptococcal glomerulonephritis develops how?
isease develops transiently when
streptococcal antigen–antibody complexes in the blood lodge in the
glomeruli (filtration membranes of the kidney) and cause inflammation,
a serious condition called nephritis.
Streptococcus pneumoniae
Causes invasive lung infections
* Typically as secondary infections to other
respiratory disorders.
* Encapsulated strains of S. pneumoniae are
virulent and invasive.
Streptococcus pneumoniae capsule
- enables the cells to resist phagocytosis
- generate a strong host inflammatory response
Pneumonia results from
the accumulation of recruited phagocytic cells and fluid
Cells of S. pneumoniae can then spread from the focus of infection as a
bacteremia
* infecting the bones
* Infecting middle ear
* Infecting heart valves (endocarditis)
S. pneumoniae infection is often the cause of death
n elderly persons whose death is reported to be from “respiratory failure.”
Older vaccine treatment for S. pneumoniae
An older vaccine
* widely used in adults
* consisted of a mixture of 23 capsular polysaccharides from the most prevalent pathogenic strains.
* is recommended for those over age 60, healthcare providers, individuals with compromised immunity, and any other high-risk population.
Newer vaccine for S.Pneumoniae
A newer conjugate vaccine called PREVNAR 13®
* an update of the traditional vaccine.
* It is effective against the 13 S. pneumoniae strains most commonly seen today
* is recommended for adults age 50 or older.
S. Pneumoniae treatment
- S. pneumoniae infections typically respond to penicillin therapy
- up to 30% of pathogenic isolates exhibit resistance to this penicillin.
- Resistance to the antibiotics erythromycin and cefotaxime is also found
in some strains - all strains have been found sensitive to vancomycin, an antibiotic held in
reserve for treating pneumonia and several other bacterial diseases
where antibiotic resistance is widespread.
Diphtheria
a severe respiratory disease that typically infects young
children, caused by Corynebacterium diphtheriae
Diphtheria bacteria description
a gram-positive, nonmotile, and aerobic club-shaped bacterium
that forms small, smooth colonies on blood agar plates
Pertussis
“Whooping Cough”
a serious respiratory disease that mostly affects children but
can cause serious respiratory disease in adults as well,
caused by Bordetella pertussis
Pertussis bacteria description
a small, gram-negative, aerobic coccobacillus
Cells of diphtheria
Cells of C. diphtheriae from airborne droplets
* Infecting the tissues of the throat and tonsils
and typically causing swelling of the neck.
Pseudomembrane
Throat tissues respond to C.
diphtheriae infection by forming a characteristic
lesion consisting of damaged host cells and cells
of C. diphtheriae
Pathogenic strains of C. Diphtheria
carry a lysogenic
bacteriophage whose genome encodes a powerful exotoxin
called diphtheria toxin that inhibits protein synthesis in the
host, leading to cell death.
Death from diphtheria is due to a combination of
- partial suffocation by the pseudomembrane
- tissue destruction by diphtheria exotoxin
Diphtheria Diagnosis
Nasal or throat swabs are used to inoculate blood agar containing tellurite or Loeffler’s medium, a selective medium that inhibits the growth of most other respiratory pathogens.
Prevention of C. Diphtheria
a highly effective toxoid vaccine, part of the DTaP (diphtheria toxoid, tetanus toxoid, and acellular pertussis) vaccine
* Diphtheria is all but absent from developed countries where this vaccine is widely used.
Treatment of Diphtheria
Penicillin, erythromycin, and gentamicin are effective treatments for diphtheria
* in life-threatening cases, diphtheria antitoxin (an antiserum to diphtheria toxoid produced in horses) may be administered in addition to antibiotic therapy.
Pertussis
Acute, highly
infectious respiratory
disease
* Infants less than 6
months old (too young
to be vaccinated)
* highest incidence
of disease
* the most severe
symptoms.
Cells of B pertussis
attach to ciliated host cells of the
respiratory tract
* Excrete pertussis exotoxin
B pertussis produces
endotoxin, which may induce
some of the symptoms of whooping cough
Whooping cough is characterized by:
characterized by a recurrent, violent
cough that can last up to 6 weeks.
Where does the whooping sound come from?
Spasmodic coughing: a whooping sound results from the patient
inhaling deep breaths to obtain sufficient air.
pertussis prevention
Vaccination protocols
Treatment of pertussis
- Whooping cough can be treated with ampicillin, tetracycline, or
erythromycin - The immune response is as important as antibiotics in ridding the
pathogen from the body.
Mycobacterium TB was discovered by
Robert Koch, the founder of the field of medical
microbiology, isolated and described the
causative agent of tuberculosis, in 1882
Mycobacterium Leprae
causes leprosy (Hansen’s disease)
Mycobacteria are
gram positive bacteria
acid fast from waxy mycotic acid constituent of their cell walls
Mycolic acid allows organisms
retain the red dye
carbol-fuchsin after a mycobacterial smear on a slide is
washed in 3% hydrochloric acid in alcohol.
Colonies of M. tuberculosis grow
Slowly on plates and have a
characteristically wrinkled morphology.
Primary infection TB
Results from inhalation of droplets containing M.
tuberculosis, after which the bacteria settle in the lungs
and grow.
Tuburcles
The host mounts an immune response to M.
tuberculosis, resulting in the formation of aggregates of
activated macrophages
postprimary infection (reinfection)
In most individuals the infection is asymptomatic.
* The infection
* hypersensitizes the individual to M. tuberculosis
* typically protects the individual against postprimary infections
