Viral Respiratory Tract Infections Flashcards
URTI
Upper Respiratory Tract Infections
Very common, often viral
Can predispose patient to secondary more severe illness
Rhinitis
Congestion in nose
Coryza
Common Cold
Rhinoviruses Parainfluenzas Coronaviruses Respiratory Syncytial Viruses (RSV) Adenoviruses Enteroviruses
Pathogen(s) responsible for Pharyngitis/Tonsilitis
Caused by viruses or bacteria
Bacteria is: Strep pyogenes
Infectious mononucleosis
Glandular Fever
Syndrome
Pharyngitis, lymphadenopathy, fever, malaise
Atypical mononuclear cells in peripheral blood
Can be caused by Epstein-barr virus, cytomegalovirus (CMV), toxoplamosis, HIV
Syndrome
Constellation of symptoms and signs, not an aetiological diagnosis
Croup
Seen in young children, characterised by wheeze due to narrowed airways
Epiglottitis
Bacterial
potentially life-threatening
Largely caused by an influenza virus
LRTI
Lower Respiratory Tract Infections
Influenza
Respiratory syncytial virus
SARS-CoV-2
Rarely: CMV Varicella Measles MERS/SARS
Types and Subtypes of Influenza viruses
A, B or C
- on basis of internal proteins; nuclear and matrix proteins
Subtypes - A only
On basis of surface proteins HA, NA (Haemagglutinin & Neuraminidase)
16HA, 9NA known - each differs by >20% sequence
e.g. A/Sydney/99/3 (H3N2)
Flu-like illness
2 Major components
- Respiratory tract symptoms, e.g. rhinitis/cough/shortness of breath
- Systemic symptoms, e.g. fever/headache/myalgia
Pathogenesis of influenza
Pneumotropic virus - infects cells of respiratory tract/alveoli
Cytolytic/cytocidal
Infection strips off respiratory epithelium
Sputum has rounded up dead epithelia
Removes 2 innate defence mechanisms - mucous secreting cells and cilia
Causes interferon production - Circulates in blood and causes systemic symptoms
Complications of influenza
Pneumonia
- Primary influenza pneumonia - mononuclear cell infiltrate
- Secondary bacterial pneumonia - granulocyte infiltrate
Cardiovascular complications
CNS complications
- Encephalitis
High risk patients for influenza
Those with comorbidities
- Lung disease
- Cardiac disease
- Renal disease
- Endocrine disease/diabetes
- Liver disease
- Immunodeficiency
- > 65 years
- Pregnancy/young children
Influenza epidemiology
Annual winter epidemics associated with excess deaths, hospitalisations and other serious consequences
Antigenic Drift
Occurs in influenza A and B
Accumulation of mutations in a virus in certain regions (HA and NA specifically)
The epitopes are the parts that the immune system forms immunity to but is also the part that the virus mutates rapidly, allowing for rapid reinfection
Antigenic shift
Remember this vs antigenic drift because it’s worse so you go like oh shi(f)t
Virus mixes with animal/other virus to make a new subtype with antigens we are drastically unfamiliar with that are far more infectious; can cause pandemics
