Respiratory Tract Infections: Viral Infections Flashcards
Name some upper respiratory tract infections
sinusitis otitis media pharyngitis tonsillitis epiglottitis tracheitis rhinitis
Cause of common cold/coryza
rhinoviruses, parainfluenza viruses (babies)
coronavirsues
Cause of pharyngitis/tonsillitis
viruses (adenoviruses)
bacteria - strep pyogens
Croup
young children
inspiratory stridor due to narrowed airways
viruses: paraflu, RSV
Epiglottitis
bacterial: haemophilus influenzae type b
potentially life-threatening, can block off upper airway
Difference between URTI and LRTIs
URTI: common, relatively trivial
LRTI: potentially life-threatening, viruses and bacteria
Viruses that cause LRTI
2 most common: influenza and respiratory syncytial virus
rare: varicella zoster, measles, MERS/SARS/coronavirus
Viruses that cause infectious mononucleosis
Glandular fever
Epstein-Barr virus, cytomegalovirus, toxoplasmosis, HIV serconversion
(atypical mononuclear cells in peripheral blood)
Symptoms of infectious mononucleosis
pharyngitis, lymphadenopathy (cervical, generalised), fever, malaise
What happens in the body when E-B virus is present?
increased number of activated CD8 positive T cells
cytotoxic, causes proliferation of B cells
Structure of influenza viruses
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
Types of influenza viruses
A,B or C - on basis of internal proteins NP, matrix
only A has subtypes - on basis of surface proteins, HA and NA
How many of each types of HA and NA are known and why is this important?
16 HA, 9 NA
each AA sequence differs by >20%, allows survival due to mutation
Clinical features of influenza
respiratory tract symptoms - rhinitis, cough, SoB
systemic symptoms - fever, headache, myalgia (muscle aches and pains)
Pathogenesis of influenza
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
Complications of influenza
2 types of pneumonia in respiratory tract:
primary viral - mononuclear cell infiltrate
secondary bacterial - PMNL infiltrate
cardivascular
CNS - encephalitis after respiratory symptoms
High risk for influenza
- pre-existing diseases eg. lung, cardiac, endocrine, immunodeficiency
- > 65 years
- pregnant women, children (0-5 years)
What is a pandemic? Relate to influenza
epidemic of disease that has spread across a large region
unpredicatable, world-wide epidemics with high mortality each winter
What is an epidemic? Relate to influenza
a widespread occurrence of an infectious disease in a community at a particular time
Why is there an annual epidemic of influenza?
antigenic drift
antigenic shift
What is antigenic drift?
random, spontaneous mutation in viral genes encoding HA and NA, causing 1% AA sequence change
mutations clustered within key epitopes in HA an NA
How does antigenic drift cause epidemics of influenza?
occurs in influenza A and B viruses
accounts for interpandemic epidemics ie. year on year recurrence of infection
Describe antigenic shift using example of influenza
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
What influenza type does antigenic shift occur in and how does this allow epidemics of influenza?
type A
>20% AA difference leading to emergence of new pandemic strains against which the population has no pre-existing immunity
