Respiratory Tract Infections: Viral Infections

Question 1

Name some upper respiratory tract infections

Answer 1

sinusitis
otitis media
pharyngitis
tonsillitis
epiglottitis
tracheitis
rhinitis

Question 2

Cause of common cold/coryza

Answer 2

rhinoviruses, parainfluenza viruses (babies)

coronavirsues

Question 3

Cause of pharyngitis/tonsillitis

Answer 3

viruses (adenoviruses)

bacteria - strep pyogens

Question 4

Croup

Answer 4

young children
inspiratory stridor due to narrowed airways
viruses: paraflu, RSV

Question 5

Epiglottitis

Answer 5

bacterial: haemophilus influenzae type b

potentially life-threatening, can block off upper airway

Question 6

Difference between URTI and LRTIs

Answer 6

URTI: common, relatively trivial
LRTI: potentially life-threatening, viruses and bacteria

Question 7

Viruses that cause LRTI

Answer 7

2 most common: influenza and respiratory syncytial virus

rare: varicella zoster, measles, MERS/SARS/coronavirus

Question 8

Viruses that cause infectious mononucleosis

Answer 8

Glandular fever
Epstein-Barr virus, cytomegalovirus, toxoplasmosis, HIV serconversion
(atypical mononuclear cells in peripheral blood)

Question 9

Symptoms of infectious mononucleosis

Answer 9

pharyngitis, lymphadenopathy (cervical, generalised), fever, malaise

Question 10

What happens in the body when E-B virus is present?

Answer 10

increased number of activated CD8 positive T cells

cytotoxic, causes proliferation of B cells

Question 11

Structure of influenza viruses

Answer 11

segmented negative ssRNA genome
8 segments which encode for 11 proteins
eg. segement 4 - haemagglutinin; segment 6 - neuraminidase
HA and NA are external attachment proteins

Question 12

Types of influenza viruses

Answer 12

A,B or C - on basis of internal proteins NP, matrix

only A has subtypes - on basis of surface proteins, HA and NA

Question 13

How many of each types of HA and NA are known and why is this important?

Answer 13

16 HA, 9 NA

each AA sequence differs by >20%, allows survival due to mutation

Question 14

Clinical features of influenza

Answer 14

respiratory tract symptoms - rhinitis, cough, SoB

systemic symptoms - fever, headache, myalgia (muscle aches and pains)

Question 15

Pathogenesis of influenza

Answer 15

pneumotropic virus infects cells lining the respiratory tract, down to the alveoli
ie. cytolytic - strips off respiratory epithelium
removes mucous secreting cells and cilia which are defense mechanisms
interferon production causes systemic response

Question 16

Complications of influenza

Answer 16

2 types of pneumonia in respiratory tract:
primary viral - mononuclear cell infiltrate
secondary bacterial - PMNL infiltrate
cardivascular
CNS - encephalitis after respiratory symptoms

Question 17

High risk for influenza

Answer 17

1. pre-existing diseases eg. lung, cardiac, endocrine, immunodeficiency
2. > 65 years
3. pregnant women, children (0-5 years)

Question 18

What is a pandemic? Relate to influenza

Answer 18

epidemic of disease that has spread across a large region

unpredicatable, world-wide epidemics with high mortality each winter

Question 19

What is an epidemic? Relate to influenza

Answer 19

a widespread occurrence of an infectious disease in a community at a particular time

Question 20

Why is there an annual epidemic of influenza?

Answer 20

antigenic drift

antigenic shift

Question 21

What is antigenic drift?

Answer 21

random, spontaneous mutation in viral genes encoding HA and NA, causing 1% AA sequence change
mutations clustered within key epitopes in HA an NA

Question 22

How does antigenic drift cause epidemics of influenza?

Answer 22

occurs in influenza A and B viruses

accounts for interpandemic epidemics ie. year on year recurrence of infection

Question 23

Describe antigenic shift using example of influenza

Answer 23

genetic reassortment between human and non-human viruses leading to new subtypes
human influenza A virus + avian influenza A virus reassort forming new subtype able to infect humans
eg. new segment 4 and 6 are avian (HA and NA), differ >20%, therefore virus has acquired complete different code
rest are human, therefore well-adapted to grow and replicate in human cells

Question 24

What influenza type does antigenic shift occur in and how does this allow epidemics of influenza?

Answer 24

type A
>20% AA difference leading to emergence of new pandemic strains against which the population has no pre-existing immunity

Question 25

Structure of Respiratory Syncytial virus

Answer 25

enveloped paramyxovirus

negative ssRNA encodes 9 polypeptides including 2 surface proteins: F(usion) and G(lycoprotein), not segmented

Question 26

RSV characteristics

Answer 26

highly seasonal infection
extremely common
causes LRTI in infants (0-1yrs) - bronchiolitis, pneumonia

Question 27

Mortality of RSV

Answer 27

low (<0.5%) unless, infant has:
congenital heart/lung disease (including prematurity)
immunodeficiency - congenital or acquired
required rapid diagnosis and infection control due to being acquired in hospital