Bordetella Pertussis

Question 1

morphology and general characteristics

Answer 1

gram-negative coccobacilli - resembling Haemophilus influenzae.

• strict aerobe
• fastidious and will grow slowly only on charcoal blood agar or bordet -gengou agar - 3-7 days for growth

Question 2

transmission and epidemiology

Answer 2

B. pertussis is found only in humans

• survives briefly outside the human respiratory tract
• highly communicable and is transmitted from person to person via respiratory secretions
• common in infants and children -> dangerous if within first 6 months of life

Question 3

virulence factors (5)

Answer 3

1. Filamentous hemagglutinin (Fha)- mediates adhesion to ciliated epithelial cells of the upper
   respiratory tract. Pili and agglutinogens may play a similar role in adherence
2. Tracheal cytotoxin - immobilization and destruction of ciliated epithelial cells
   -toxicity is through the inhibition of DNA synthesis.
3. Pertussis Toxin (PT) -the major virulence factor of B. pertussis; an ADPR-transferase
   - classic A-B type exotoxin:
   - active or A subunit, transfers ADP-ribose from NAD to a G protein that regulates
   adenylate cyclase activity such that the host cell cannot turn off the production of cAMP.
   - binding or B subunits which mediate attachment to carbohydrate moieties on the host cell
   surface and translocates A subunit across the membrane
   - biological effects depend on cell type involved and include histamine sensitization,
   lymphocytosis, insulin secretion, and alteration of other immune effector cell functions (decreased
   oxidative killing capacity)
4. Invasive adenylate cyclase - enters host cell and raises host cell cAMP levels
   - hemolytic and interferes with chemotaxis and superoxide production
   by PMNs
5. B. pertussis produce a hemolysin and a dermonecrotic heat-labile toxin -role in disease is unknown.

Question 4

Pathogenesis and clinical considerations

Answer 4

-extracellular organism -> initiates infection by colonizing the ciliated bronchial epithelium and rapidly multiplying - immobilization and destruction of the ciliated epithelial cells occurs with no tissue invasion or dissemination

Question 5

3 stages of the disease

Answer 5

Three stages of disease -
a. catarrhal stage (1-2 weeks)
- malaise, fever, sneezing and anorexia may be present
- profuse and mucoid rhinorrhea
- highly communicable with a large number of organisms in the nasopharynx and mucoid secretions
b. paroxysmal coughing stage (2-4 weeks)
- coughing episodes 40-50 times per day, characteristic inspiratory whoop as air is drawn through
narrowed glottis
- due to coughing and disruption of breathing, child may turn red and sometimes blue, and may
result in vomiting or choking on respiratory secretions
-lymphocytosis - elevated white blood cell counts with 70-80% lymphocytes
c. convalescent stage (3-4 weeks) - gradual fade of symptoms
Infection is usually limited to the upper respiratory tract. Infrequent complications may include:
-Bronchopneumonia due either to B. pertussis or to superinfection with organisms such as
Staphylococcus, S. pneumoniae or H. influenzae.
- Acute encephalopathy, characterized primarily by convulsions resulting in death or life-long brain
damage.

Question 6

Laboratory diagnosis

Answer 6

culture - nasopharyngeal swab- during 1st 4 weeks -> charcoal blood agar

• direct immunofluorescent assay-> sent 50%
• PCR for rapid ID followed by confirmation by culture is standard

Question 7

Immunity

Answer 7

protective immunity but not life-long. second infections are mild if they occur. antibody that prevents attachment to ciliated epithelial cells or neutralize PT may be involved . Secretory IgA may be important in nasopharyngeal secretions

Question 8

treatment

Answer 8

erythromycin is the drug of choice
only useful in the catarrhal stages of the infection
and for prophylaxis of their exposed and susceptible individuals

once paroxysmal coughing has begun - treatment is primarily supportive

Question 9

prevention and control

Answer 9

Vaccination - part of the diphtheria, tetanus acellular pertussis DTaP
- vaccinated at 2,4 and 6 months
boosters at 15-18 months and at the time of school entry are recommended.

1st gen vaccine - heat-killed prep of whole virulent organism- post vaccinal encephalopathies occurs every 100,000-300,000

2nd gen acellular vaccine- DTaP is now used - neuro complication reduced. acellular vaccine consists of Fha, pertussis toxoid and outer membrane protein and 2 fimbrial hemagglutinating antigens