influenza virus haemagglutinin surface protein (H) binds sialic acids on cell surface glycoproteins and glycolopids in the respiratory tract, allowing it to enter the cell.
how does the influenza virus prevent escaping virions from clumping together?
neuraminidase (N) on surface of virus allows it to escape by cleaving sialic acid bonds
influenza virus has a segmented genome (8 parts) so can reassort if two different viruses infect the same cell
influenza shift and drift: antigenic drift
neutralising antibodies against haemagglutinin block binding to cells
mutations alter haemagglutinin epitopes so that the neutralising antibody no longer binds
multiple reassortment events in virus genome can cause it to infect other animals eg. humans
treatment and prevention of influenza
active immunisation against haemagglutinin and neuraminidase
hand hygiene and droplet precautions
Epiglottis/ HiB
Haemophilus influenzae b infection
disease of adults
symptoms include:
drooling, dysphagia, distress
risk of sudden complete airway obstruction
ENT emergency
croup/ laryngotracheobronchitis
inflammation of the larynx, trachea and bronchi
= upper airway obstruction, especially at the narrowed subglottic region
parainfluenza virus most common
croup symptoms
barking cough, inspiratory stridor, hoarse voice
hypoxia is a late sign and very worrying
use of accessory muscles
croup management
reduce inflammation (steroids +- adrenaline)
acute bronchitis
lower respiratory tract infection
damage to bronchial walls -> increased mucus production + oedema of bronchus = productive cough
acute bronchitis symptoms
usually viral
assoc. with URTI symptoms
may be wheeze/ dyspnoea
no fever/ systemic upset
cough continues after infection cleared as bronchial wall has to heal - may take weeks
bronchiolitis
acute infection of the epithelial cells lining the small airways
results in oedema, increased mucus production, cell death
the debris and oedema obstructs the distal airways
disproportionate narrowing in expiration means air trapping and wheeze
what is the cause of bronchiolitis?
majority caused by RSV (respiratory syncitial virus)
usually children <2yrs
bronchiolitis symptoms
coughwheeze and tachypnoea
increased work of breathing
fever; corzya
bronchiolitis diagnosis and treatment
viral nose/throat swab or respiratory secretions for RT-PCR
treatment = supportive care
pneumonia - pathophysiology
pneumonia = infection of the lung parenchyma
alveoli full of inflammation = blocks oxygen transfer
pneumonia symptoms
fever, breathlessness, cough, sputum production
hypoxia, increased respiratory rate
pleuritic chest pain
sepsis
radiology - diagnosis of pneumonia
requires infiltrates on a plain CXR with supporting clinical features
consolidation: alveoli and bronchioles completely filled with inflammatory debris/pus/pathogens
heart borders or diaphragm obscured due to the loss of solid-gas interface
air bronchograms- air in larger bronchi outlined by surrounding consolidation
classifications- most useful:
community vs hospital-acquired - useful as pathogens involved differ in their % contribution
community-acquired pneumonia pathogens
Streptococcus pneumoniae
Haemophilus influenzae
Mycoplasma pneumoniae
Legionella pneumophila
Staphylococcus aureus
streptococcus pneumoniae
commonest organism - gram positive diplococci, acquired in nasopharynx