Respiratory Pathogens

Question 1

P mechanism of spread

Answer 1

Aerosols are important for person-to-person transmission of
many infectious diseases.
Most pathogens survive poorly in air; thus, they are
effectively transmitted only over short distances

Question 2

Respiratory tract environments

Answer 2

Different pathogens characteristically colonize the respiratory
tract at different levels.
The upper and lower respiratory tracts offer different
environments (temperature, air flow, pH, etc.) and favor
different microbes.

Question 3

GAS

Answer 3

group A streptococci
commonly found in low numbers in the
upper respiratory tract of healthy individuals

Question 4

GAS diseases

Answer 4

Pharyngitis
Scarlet fever
Septicaemia
Toxic shock syndrome
Rheumatic fever
Rarely: Cellulitis and fasclitis

Question 5

pharyngitis

Answer 5

Streptococcus pyogenes (Group A Streptococcus; GAS) is a Gram-positive host-adapted bacterial pathogen.
It most often causes mild human infections such as pharyngitis or impetigo

Question 6

Scarlet fever

Answer 6

A Strep A infection (usually beginning with the throat) where erythrogenic
toxins such as SpeA, produced by the bacterium when it is infected by a bacteriophage (T12) causes a high fever, rash and ‘strawberry tongue’ that used to cause significant mortality in
children.

Question 7

Septicaemia

Answer 7

‘blood poisoning’ an infection of the bloodstream that can lead to septic shock
and death (50% mortality rate).

Question 8

Rheumatic fever

Answer 8

An inflammatory disease that affects the heart, joints, skin, and brain

Question 9

Rheumatic heart disease

Answer 9

Type of rheumatic fever
-An autoimmune response following a poorly treated Strep A infection
-The disease typically develops two to four weeks after a streptococcal throat infection. -The exact mechanisms that lead to
the disease are not clear, but it is understood that molecular mimicry of the bacterium results in the immune system targeting the heart valves, which results in valve scarring and damage.

Question 10

cellulitis + fasciitis

Answer 10

Streptococcus pyogenes under rare circumstances can occasionally cause
sudden and severe tissue infections such as: cellulitis, a subcutaneous skin
infection or erysipelas.
-fasciitis = (flesh eating disease)

Question 11

Diphtheria

Answer 11

A severe upper respiratory disease that typically infects children and caused by Corynebacterium diphtheriae, a Grampositive bacterium that forms irregular rods during growth

Question 12

Corynebacterium diphtheriae mechanism of spread

Answer 12

-Spreads by airborne droplets and enters the body via the respiratory route.
-Pathogenic strains lysogenized by bacteriophage β produce a powerful exotoxin that causes a pseudomembrane in the patient’s throat.
-Death due to a combination of partial suffocation by the pseudomembrane and tissue destruction in various organs due to dissemination of the toxin

Question 13

Resistance against Corney bacterium

Answer 13

Previous infection or immunization provides resistance.

Question 14

symptoms of diptheria

Answer 14

A swollen neck is a common symptom of
diphtheria.
-The pseudomembrane in
an active case of diphtheria restricts airflow and swallowing and is associated with a severe sore throat

Question 15

diptheria treatment

Answer 15

-Prevention of diphtheria is achieved by the DTP3/DTaP (diphtheria toxoid, tetanus toxoid, and acellular pertussis) vaccine.
-Antibiotics can be used for active infections/Diphtheria antitoxin is available for acute cases because antibiotics
take time that patients fighting off an exotoxin may not have

Question 16

Pertussis

Answer 16

-Also known as whopping cough
-Caused by Bordetella perussis
-Pertussis is an acute, highly infectious respiratory disease that frequently occurs in children but also in adolescents and adults.

Question 17

Pertusis symptoms

Answer 17

-It is characterized by a recurrent, violent cough that may lead to fatal complications such as pneumonia, pulmonary hypertension and encephalopathy.
-Usually the disease starts with mild, cold-like symptoms but this is followed by a prolonged
violent cough that can last for up to 10 weeks. -Small children may struggle to breathe.
-Inadequate vaccination has led to consistent upward trend of infections in recent years.

Question 18

Trend of pertusis infections

Answer 18

rises from 20% in 1981 to a local maximum at about 70% in 1990, then remains steady till 2001; then it rises to a
maximum at 85% in 2016 and remains steady till 2018

Question 19

Pertusis mechanism of infection

Answer 19

-Surface proteins of B. pertussis, including filamentous hemaglutinin and pertactin act as
adhesins and allow attachment to the epithelium in the upper respiratory tract.
-In infants, the bacteria form lower respiratory tract infections.

Question 20

Petusis mechanism of disease

Answer 20

-Toxins such as tracheal cytotoxin (TCT), a fragment of peptidoglycan, kills ciliated epithelial cells preventing mucus and debris from being removed from the upper respiratory tract.
-It is thought that pertussis toxins also cause elevated numbers of white blood cells in the
lung arteries causing a blockage of these vessels, known as pulmonary hypertension.
In infants this results in hypoxia (lack of oxygen) and brain damage/death via
encephalopathy, cerebral hemorrhage and cortical atrophy

Question 21

Treatment of pertusis

Answer 21

Antibiotics

Question 22

Tuberculosis

Answer 22

A respiratory disease, primarily of the lungs although it can also manifest in the brain, spine, kidneys. In fact, any part of the body

Question 23

Causative agent of TB

Answer 23

The causative agent is Mycobacterium tuberculosis, which was established
by Robert Koch in 1882. At that time TB killed 1 out of every seven people in
Europe. It still kills millions of people each year (1.5 million in 2020). South
Africa has one of the highest burdens of TB in the world.

Question 24

Mycobacterium descirption

Answer 24

Mycobacteria are aerobic rod-shaped bacteria that are unusual in that they have unconventional cell walls
which are rich in lipids called mycolic acids.

Question 25

Mycobacterium detection

Answer 25

m resistant to gram staining, instead they are stained with carbol-fuchsin and treated with
acid. Retention of the dye by the mycolic acids makes them acid fast.

Question 26

Cell type TB infects

Answer 26

The mycobacterium is phagocytosed by resident macrophages with the alveoli. The bacterium is potentially killed by this process
or survives within the specialised endosomes in which they were phagocytosed, called phagosomes.
M. tuberculosis is able to reproduce inside the macrophage
The primary site of infection in the lungs is known as the Ghon focus,

Question 27

Granuloma

Answer 27

-infected macrophages with TB, attract other cells and immune cells (macrophages, epithelioid cells, T lymphocytes, B
lymphocytes, and fibroblasts) which aggregate about the infected focus to form and aggregate called a granuloma.
-This structure prevents the bacterium from accessing lung tissue and prevents dissemination but also protects it from immune targeting.
-Bacteria in the granuloma become dormant but may be reactivated and reestablish infections in distal sites. The granulomas are
usually filled with dead cells that will eventually form cavities. These can be seen by X-Ray.
-Tissue destruction and necrosis are often balanced by healing and fibrosis

Question 28

TB latency

Answer 28

Approximately 9 out of 10 (90%) of TB infections that are not eliminated are latent and asymptomatic.
10% of latent infection will progress to overt, active tuberculous disease.

Question 29

Treatment of TB

Answer 29

Treatment of TB requires long courses of multiple drugs. However, the immergence of multi-drug resistant M.
tuberculosis strains sometimes renders these combinations ineffective. It is also often difficult to target dormant
bacteria within granulomas.

Question 30

TB drugs

Answer 30

Isoniazid
-Rifampicin
-Pyrazinamide
-Ethambutol