19 Upper respiratory tract infections Flashcards
Introduction
We distinguish between upper and lower respiratory tract, even though it is a continuum. Some organisms have a preference (e.g nasopharynx - cornaviruses/ rhinoviruses)
Proximal to distal - Rhinitis, sinusitis, pharyngitis, laryngitis, tracheitis, bronchitis, bronchilotis, pneumonia
Some microorganisms are restricted to surface of epithelium. Some spread to other parts of body before returning to respiratory tract/ oropharynx/ salivary glands e.g mumps
What are “professional “ invaders, and “secondary invaders”
Professional successfully infect the normal healthy respiratory tract, and can evade local host defences, e.g attachment mechanisms for respiratory viruses
Secondary invaders cause disease only only when host defences are already impaired e.g staph aureus after influenza
Normal flora of respiratory tract
Common >50% people
Occasional <10% people
Streptococci Neisseria spp Moraxella Corynebacterium Bacteroides Candida albicans Haemophilus influenzae
Streptococcus pneumoniae
Streptococcus pyogenes
Neisseria meningitidis
Normal flora of respiratory tract
Uncommon <1% people
Residents in latent state in tissues
Corynebacterium diptheria
Klbesiella pneumoniae
Pseudomonas
E. Coli
Pneumocystis jirovecii Mycobacterium TB CMV EBV HSV VZV
Pathogens which gain access via upper respiratory tract through the surface
Short incubation period. Local defences breeched, and infection established before adaptive immune response active
Rhinoviruses Influenza Streptococci in throat Chlamydia (conjunctivitis) Diptheria Pertussis Candida albicans
Pathogens which gain access via upper respiratory via spreading through body
Little or no entry in respiratory system. Pathogen spreads throughout body, returns to surface for final multiplication and shedding. Adaptive immune system important in recovery, longer incubation (weeks)
Measles - respiratory tract Mumps - salivary gland Rubella EBV - salivary gland CMV - salivary gland
Professional invaders
What are examples of pathogens which -
- Adhere to normal mucosa (in spite of mucociliary system)
- Ability to interfere with cilia
Respiratory viruses - influenza, rhinovirus
Strep pyogenes
Strep pneumoniae
Chlamydia
Bordetella pertussis
Mycoplasma pneumoniae
Strep pneumoniae (pneumolysin)
Professional invaders
What are examples of pathogens which -
- Resist destruction by alveolar macrophage
- Damage local mucosa/ submucosal tissues
Legionella
TB
Corynebacteriym diptheriae (toxin) Strep pneuomniae (pneumolysin)
Secondary invaders
What are examples of pathogens which -
- Infect after initial damage by respiratory virus
- Infect when local defences impaired (e.g cystic
fibrosis) - Infect in chronic bronchitis, local foreign body or tumour
Staph aureus
Strep pneumoniae
Staph aureus
Pseudomonas
Haemophilus influenzae
Strep pneumoniae
Secondary invaders
What are examples of pathogens which -
- Infect when immune response depressed
- Infect when resistance depressed - elderly, alcoholism, CKD, liver disease
Pneumocystis jirovecii
CMV
TB
Strep pneumoniae
Staph aureus
Haemophilus influenzae
Respiratory viruses cause common cold. They induce flow of virus rich fluid (rhinorrhoea), and sneezing triggers release of virus particles into air - aerosol transmission.
Most respiratory viruses have surface molecules which allows them to bind to microvilli, so they are not washed away in normal respiratory secretions.
Once first cell is infected, virus progeny from spread to neighbouring cells and via surface secretions to new sites on mucosal surface. Damage to epithelial cells and release of inflammatory mediators such as bradykinin lead to cold type symptoms
How are most virus infections diagnosed?
Viral PCR used these days
Use throat swabs
Avoid nasopharyngeal aspirates, as risks aerosol production of pathogen
What is the attachment mechanism for the following viruses and what disease can it cause
- Rhinovirus (>100 types)
- Enteroviruses including:
Coxsackie virus A (24 types)
Echoviruses (34 types)
Enteroviruses (116 serotypes)
capsid protein binds to ICAM-1 (intercellular adhesion molecules expressed on wide variety of normal cells) - common cold
Capsid protein binds to ICAM-1
Common cold, hand foot and mouth
What is the attachment mechanism for the following viruses
- Influenza (A, B, C)
- parainfluenza (1,2,3,4)
- RSV (A, B)
Haemagglutinin binds neuraminic acid containing protein on cell surface
Viral envelope proteins binds to glycoside on cell
G protein on virus attaches to receptor on cell
What is the attachment mechanism for the following viruses and what disease does it cause
- Coronaviruses (several types)
- Adenovirus (41 types)
Viral envelope protein binds to glycoprotein receptors on cell - common cold, SARS, Middle East respiratory syndrome coronavirus (MERS CoV)
Penton fibre binds to cell receptor
Pharyngitis, conjunctivitis, bronchitis
Common viruses which cause acute pharnygitis 8
Viruses inevitably encounter the submucosal lymphoid tissue that form a defensive risk around the oropharynx.
Rhinoviruses Coronavirus Adenovirus Influenza Parainfluenza - more severe than common cold Enteroviruses including Coxsackie A16 - small vesicles on hard palate/ tongue (hand, foot and mouth) EBV HSV1 - hard palate/ tongue vesicles
Common bacteria which cause acute pharyngitis
Streptococcus pyogenes - usually 5-10 years old
Neisseria gonorrhoeae - often asymptomatic
Corynebacterium diptheriae - can be severe
Haemophilus influenzae - epiglottitis
Borrelia vincentti - Vincent’s angina
Routes of transmission for CMV
CMV humans are natural hosts
Saliva Blood Organ donor Urine Semen/ cervical Breast milk
CMV causes silent infection, often asymptomatic.
Spreads to lymphoid tissues, then systemically via circulating lymphocytes and monocytes to involve lymph nodes/ spleen and epithelial cells of salivary gland/ kidney tubules/ cervix/ semen, where it is shed to outside world.
How does CMV cause disease
Inhibits T-cell response by interfering with MHC class I expression Induces Fc receptors on infected cells to help spread
Causes no illness in children, mild disease in adults. Cell mediated immunity helps keep virus at bay, but cannot clear it, remains throughout life. Can cause disease one immunity impaired
