Respiratory infections Flashcards
State 3 common lung bugs
Streptococcus pneumoniae
Mycobacterium tuberculosis
Legionella Pneumoniae
Influenze Rhinovirus Aspergillus fumigateurs SARS Pneumocystis jirovecis
What is the difference between an upper respiratory tract infection and a Lower respiratory tract infection?
URTI affects nasal cavity, pharynx and larynx
LRTI affects trachea, bronchi, bronchioles and alveoli
Describe the pathogenesis of infection in lung.
Lungs constantly exposed to particulate material and microbes from upper airway
Lower airways usually devoid of conventional pathogens, in infection this is untrue
How does the innate immunity and acquired immunity keep the lower tract sterile?
INNATE
- Cilia- mucocilary escalator removes debris and pathogens
- Alveolar macrophages secrete antimicrobials; engulf and kill pathogens; recruit other WBCs; process and present antigens to T cells
ACQUIRED
- B/T cell responses- essential for intracellular pathogens inc. mycobacterium, viruses and fungi
- IgA secreted by plasma cells interferes with adherence and viral assembly
Explain the role of IgA in preventing respiratory infections in the lungs.
Forms additional epithelial protective barrier which prevent microbial adherence to epithelial surface and inhibits viral infections (influenza) by interfering assembly processes
Also binds pathogens for phagocytosis and antibody-dependent cell-mediated cytotoxicity
In response to infection, inflammation occurs. How does this occur and what are the cardinal signs?
Give an example of an inflammatory condition in both the upper and lower respiratory tract.
Redness, heat, loss of function, pain, swelling
- Vasodilation
- Increased vascular permeability
- inflammatory cells infiltrate area
URT: Rhinitus, sinusitis, pharyngitis, tonsillitis, laryngitis
LRT: Bronchitis, Bronchiolitis, Pneumonia, P.tuberculosis, P.abscesses, Empyema
Describe the common cold(URTI) in terms of epidemiology, aetiology and transmission
Recurs 5/7x in preschool kids; 2/3x per year in adulthood
Accounts for 40% of workdays lost
> 200 viruses cause it with commonest being rhinovirus (30-50%)
Transmission:
- Hand contact- direct/indirect . Viable on skin <2hrs, longer on surfaces
- Droplet
Infectious period: 2/3 days
Symptomatic period: 3-10 days - 2 weeks in 25% of ppl
How does the cold compare to the flu?
ONSET: Cold appears gradually, Flu quickly within hours
TARGET: Cold mainly nose and throat, Flu more than just nose and throat (systemic)
EFFECT: Cold no fever and ill but functional, Flu is exhausted and unwell (non functional),high fever.
Describe the aetiology and epidemiology of influenza
What does uncomplicated influenza look like?
Caused by influenza A or B
Occurs in outbreaks and epidemics worldwide- in winter (so swaps hemispheres over the course of the year)
Infectious period: 1-4 days
Abrupt onset of fever (38-41), headache, myalgia, malaise, cough, sore throat, nasal debilitating
ACUTELY DEBILITATING
What can cause influenza to become complicated?
Which groups of people are at risk of this?
- Primary viral pneumonia
- Secondary bacterial pneumonia
- CNS disease
Those on immunosuppressants or with chronic illness
Pregnancy (or 2 weeks postpartum)
<2y/o or >65
BMI >40
Briefly outline how viruses replicate
Attachment Penetration Synthesis of new components Assembly Release
Viruses must be able to replicate inside a cell, move from one infected cell to another and new host, as well as develop mechanisms to evade host defences
Describe how an influenza viron enters a host cell
Express hemogglutinin surface protein (H) which bind to sialic acid receptor on host cell in respiratory tract
This binding allows the iron entry into the cell
The iron also expresses neuraminidase (N) which allows it to escape host cell by cleaving silica acid bonds- otherwise the escaping irons all clump together
Suggest a target for treatment of influenza
Immunisation against Hemogglutinin surface protein (H) and Neurominidase (N)
Tamiflu = osel tamivir= (N) inhibitor
In terms of influenza, describe viral SHIFT
The influenza virus has a segmented genomes (8 parts) so in the case where a cell is co-infected by 2 or more different viruses they can reassort themselves which leads to viral diversity which is important in the evolution of influenza virus
This only occurs in influenza A as it can infect different species of animals. When viruses infect different species they adapt, by chance if one of reassorted viruses is infectious in humans –> swine flu e.g.
In terms of influenza, describe viral DRIFT
This can occur in influenza A or B
They have some of their own synthesis machinery- RNA dependent RNA polymerase. This isn’t very good at its job=mistakes=point mutations
These point mutations accumulate and change the shape of hemogglutinin surface proteins and/or neuraminidase such that it is no longer detected by the bodies pre-made antibodies
