RHS15 - Respiratory Tract Infections 5

Question 1

What is acute bronchitis? What are its most common causes?

Answer 1

Inflammtion of the bronchi due to an upper airway infection resulting in a cough lasting more than five days

• Causes are usually viral
  
  • Influenza A and B
  • parainfluenza
  • Other typical URTI viruses

Question 2

What other disease can acute bronchitis be easily mistaken for? How do you tell the difference?

Answer 2

A regular URTI or pneumonia

• Indistinguishable from a URTI in the first few days but once there is LRT involvement it’s either acute bronchitis or pneumonia
• Acute bronchitis will not present with high grade fever, pleuritic chest pain, or SOB. Pneumonia will

Question 3

What is croup? What usually causes it?

Answer 3

Croup (aka - laryngotracheitis/laryngotracheobronchitis) is respiratory illness in children from 6mo - 3yo characterized by:

• Inflammation in larynx and sub-glottic area leading to the xray steeple sign (refer to image)
• Inspiratory stridor
• Cough (barking cough in infants)
• Hoarseness

Usually caused by human parainfluenza virus 1 (HPIV1)

Question 4

Answer 4

E

Question 5

What viral family are the HPIV and RSV viruses from?

Answer 5

Paramyxoviriniae

Question 6

Give the genome and envelope type for the HPIV and RSV viruses.

Answer 6

• All paramyxoviridae viruses have (-)ssRNA and an envelope

Question 7

Important note about synctium forming viruses.

Answer 7

• Because they mostly stay within the cells, they evade the immune system very well
• These viruses often start in the URT and migrate down into the LRT

Question 8

List the key HPIV viral proteins and say what they do.

Answer 8

• Fusion Protein [F] - viral entry and synctium formation (immune evasion)
• Phosphoprotein [P] - blocks interferon release (immune evastion)
• Hemagglutinin [H] - viral entry
• Neuraminidase [N] - viral exit
• Polymerase [L] - replicate genome
• Matrix [M] - assemble viral particles

Question 9

List the key RSV viral proteins and say what they do

Answer 9

• F protein - viral entry and synctium formation (immune evasion)
• Glycoprotein [G] - viral entry and exit

Question 10

How are HPIV/RSV transmitted? What are the predisposing factors for contracting these viruses?

Answer 10

• Respiratory droplets (aerosol for one hour)
• Predisposing factors
  
  • Vitamin A deficiency
  • Lack of breastfeeding
  • Malnutrition
  • Overcrowding
  • Environmental smoke or toxins

Question 11

What is bronchiolitis? What clinical feature is almost always caused by bronchiolitis?

Answer 11

• Inflammation of the bronchioles and small bronchi
• Wheezing and/or crackles (rales) in a child <2yo (asthma is usually not diagnosed in children <5yo)

Question 12

What is the most common cause of bronchiolitis? What are its clinical features?

Answer 12

• RSV
• Clinical features
  
  • <2yo
  • URIT Sx first
  • Wheezing and/or crackles (rales)
  • Fever < 38.3C (101F)
  • Cough
  • Respiratory Distress

Question 13

What are the risk factors for bronchiolitis?

Answer 13

• Prematurity
• Low birth weight
• Congenital heart disease
• Chronic pulmonary disease
• 2nd hand smoke
• Overcrowding/day care

Question 14

What is whooping cough? What causes it?

Answer 14

Whooping cough (aka - pertussis or hundred day cough) is a LRTI & URTI caused by bordetella pertussis and is characterized by a very persistent cough (up to 100 days).

Question 15

What type of bacteria is bodetella pertussis?

Answer 15

Gram negative coccobacillus

Question 16

What are the clinical features of whooping cough?

Answer 16

• Typically occurs in children with no DTap vaccine
• Symptoms present in stages:

1. Incubation Period - no Sx 5-10 days after exposure
2. Catarrhal Stage - dry cough for 1-2weeks
3. Paroxysmal Stage - whooping cough (cough followed by sharp inhale making a “whoop” sound) for the next 1-6 weeks
4. Convalescent Stage - dry cough for next few weeks to months

Key clinical feature is dry cough at first followed by whooping cough in an unvaccinated child

Question 17

Describe the pathogenesis of pertussis. Include the relevant virulence factors

Answer 17

1. Bacterial exposure through respiratory droplets
2. Bacterial attachment to ciliated epithelium using protein adhesins (pertactin, FHA, fibria)
3. Localized tissue damage caused by dermonecrotic toxin and tracheal cytotoxin. This prevents the cilia from clearing mucus which is what causes the whooping cough
4. Systemic toxic effects caused by pertussis toxin
5. Bacterial clearance

Question 18

Describe the lab diagnostic process for whooping cough.

Answer 18

1. Nasopharyngeal sample (not throat because there are no ciliated epithelium there) taken with a pertussis swab (cotton swab will dry out sample and kill bordetella pertussis)
2. Grown in Bordet-Gengou media