Minor resp 7&8 Flashcards
(37 cards)
What parts of respiratory tract have commensal flora and which are essentially sterile
The upper tract - nasal cavity pharynx larynx have commensal flora
The lower tract - trachea , bronchi and lungs are essentially sterile
Why is the respiratory tract the most common site for infection
It has direct contact with the physical environment
Exposed to many potential pathogens
15000 litres of air breathed every 24 hours
What are common characteristics of URT infections
URT infections are usually
benign, transitory and self-
limiting and the majority are caused by viruses
What are common characteristics of LRT infections
LRTs esp. Pneumonia can be
severe.
* Bacteria are main
pathogens in LRTIs
How does the respiratory tract resist infection and what happens if this is disrupted
Respiratory tract possesses a variety of defence
mechanisms
* Generally providing very effective resistance to infection.
* Lowering of resistance usually necessary for infection.
e.g. Viral infection often precedes bacterial infection.
How do viruses infect a cell and how does this lead to tropism
Animal viruses bind to specific receptors on
the host cell surface.
* Variation in the display of receptors in
different cell-types leads to tropism
of different viruses.
– Tissue tropism (Tissues the virus has a preference for)
– Host range (which species the virus can infect)
Describe the process of viral replication
1) Virus binds to specific receptors on surface of a host cell
2) The virus delivers its genome to the host cell via uncoating (3 methods uncoating at cell membrane - measles uncoating at endosmome- hep c uncooating at nuclear membrane - adenovirus
3) Replication occurs in which the virus synthesises mRNA. 7 classes of viral genomes determines replication pathway (RNA virus replication occurs in cytoplasm DNA virus occurs in nucleus)
4) Protein synthesis- viral genes encode proteins and use the host vells ribosomes to do this.
5) Viruses leave cell by budding (enveloped) or cell lysis (non enveloped)
What is the pharmacological strategy of antivirals
Antiviral agents do NOT ‘kill’ viruses, they inhibit replication
and/or spread.
How do viral specific agents work
interact with viral proteins or nucleic acids involved
in viral entry, transcription, replication of the viral genome, assembly, and
release of infectious viral particles.
How do host directed antivirals work
modulate the activity of host factors and pathways
involved in the synthesis, processing, and transport of viral building
blocks, as well as in the development of antiviral and inflammatory
responses.
What is the Adenovirus
Extremely hardy; can survive long periods
outside the host.
* A dsDNA virus with an icosahedral capsid.
Describe what the adenovirus causes and how its transmitted
Usually cause acute respiratory disease.
– More common in young than adults.
– Persistent infection may occur in tonsils.
* Infection usually via droplet transmission.
* Outbreaks most common in winter, spring and
early summer, especially in crowded institutions.
* Multiple human serotypes
How does adenovirus present
- Typically types 1-7 responsible for c10% acute
febrile URT infections. - Fever, rhinorrhea, cough, and sore throat (3-7
days). - Adenoviral lower RTI’s may mimic RSV infection
or influenza.
– Conjunctivitis in the presence of bronchitis suggests
adenoviral infection.
How is Adenovirus treated
Disease usually mild and self-limiting; supportive/
symptomatic only.
* Some antivirals used (e.g. Ribavarin and
Ganciclovir) to treat serious infection in the
immunocompromised.
– Vaccine developed for serotypes 4 and 7.
What is coronavirus and how is it transmitted and treated ?
Most coronaviruses cause acute, mild upper
respiratory infection (i.e. a cold!): mostly in
winter/early spring.
– Responsible for approx 10–15% of colds.
* Transmission is usually via airborne droplets to
the nasal mucosa.
– Virus replicates locally in cells of the ciliated
epithelium.
* Treatment is symptomatic; hygiene measures
may reduce transmission rate.
How is influenza transmitted and how does the body response
- Transmitted in aerosols of respiratory secretions.
– Virus multiplies in the respiratory mucosa.
– most contagious in the first 3-4 days of illness. - Influenza symptoms overlap those of many other viral
URTIs.
– A number of other viruses may initially cause influenza-like
illness.
– May cause Lower respiratory tract infection. - Cell-mediated- and antibody response develop post-
infection.
– Antibody provides long-lasting immunity against the infecting
strain.
What is croup
- Acute infection of the lining of larynx,
trachea and bronchi. - Usually viral (parainfluenza
virus in 80% cases). - May also affect epiglottis (epiglottitis).
- Particularly problematic in
young children and babies. - Infection can lead to swelling and
constriction of the airways (steroid
treatment). - 60% cases resolve in 48 hrs.
What is HPV how is it transmitted and what are the 4 main types
- A Paramyxovirus (enveloped ssRNA virus).
− related to influenza viruses. - Transmission is by droplets or direct contact.
- Cause mild or severe upper and lower
respiratory tract infections.
– Responsible for 30-40% of childhood colds, croup, bronchitis
and pneumonia. - 4 main types:
– Types 1 & 2: Major cause of croup in children under 5.
– Type 3: Bronchopneumonia <1 year (second only to RSV as
cause of pneumonia and bronchiolitis).
– Type 4: Mild upper respiratory infections.
What isa rhinovirus
ssRNA virus: Probably most common infectious agent in
humans.
* Over 100 different serotypes.
– Vaccine production almost
impossible.
– Most use the Intercellular adhesion
molecule-1 (ICAM-1) as the major
cellular receptor.
* Mostly restricted to URT.
– May cause otitis media and sinusitis.
– May also exacerbate asthma, cystic fibrosis, chronic
bronchitis, and serious LRT illness. e.g. In coinfections
with RSV.
What is the pathophysiology of a cold
Some virus specificity:
– e.g. Human RV infection alters
expression of genes associated
with immune response (incl.
chemokines). These inflammatory
mediators then produce the
symptoms.
What is RSV
- A Paramyxovirus (Enveloped ssRNA
virus). - Two major antigenic subgroups, A & B.
- Two surface glycoproteins; G and F:
– G: Major attachment protein
– F: Fusion protein
– F-glycoprotein only on viral surface
membrane and highly conserved
Across both subgroups.
What are the characteristics of RSV
- Common cause of colds AND the most frequent cause of serious
respiratory disease in infants and young children. - RSV initially replicates in the nose and throat before spreading
to the LRT. - Usually self-limiting (10–14 days) but may require
hospitalisation.
– c30,000 <5 year-olds hospitalised in the UK per year.
– 33 deaths per year in children under the age of five. - Can cause severe disease in adults.
– 8,000 deaths/year in 65+.
How is RSV transmitted
Reservoir of RSV is in older children.
* Transmission is primarily by large droplets or hand-to-hand contact.
* Outbreaks occur in autumn, winter and early spring.
* Nosocomial outbreaks (paediatric wards & nurseries) major
problem
What is the pathology of RSV
Replicates in ciliated epithelial cells (middle/lower respiratory tract)
Causes:
Enzyme release → inflammation
Necrosis, mucus, fibrin → plugs airways
Otitis media common in infants
