Respiratory Viruses and atypical respiratory pathogens Flashcards
-The complexity of the various compartments of the respiratory tract, and the microbial agents which cause infections in this system. -The types of infection presenting in the respiratory system and their causes. (including common cold, laryngitis, tracheitis, bronchiolitis) -Influenza as a major respiratory disease with worldwide significance. Focussing on: Nature of the disease, viral biology and complications. Classification of flu viruses Influenza as a recurring epidemic disease, due to
Respiratory tract
Begins with inhalation
Some viruses are restricted to certain areas
Lower respiratory and upper r tract
Types of infection - surface
Surface
- local spread - stay localised to epithelial layer
- short incubation
Types of infection - systemic
Spreads from mucosal site of entry to other site in body
returns to surface for final shelling
longer incubation of a few weeks e.g MMR
Professional invaders
Infect healthy resp tract
Secondary invaders
Infect compromised tract
Infections of nasopharynx
Rhinitis/sinusitis - common cold
Rhinitis and sinusitis =
common cold
spread by aerosol
not systemic
Lytic infection
Virus adheres to ciliated epithelium
Enters cells and replicates inside cells and spread
Inflammatory response results
Common cold virus examples
Rhinovirus, influenza, adenovirus
Adenovirus
Pentagonal capsule
Resistant to desiccation
Adhesins on end of penton fibres attach to cells
dsDNA
Pharyngitis and tonsillitis
70% caused by viruses
Common complication of common colds due to surrounding infections
complication of common colds
Mumps
Paramyxovirus
airborne spread during school
Most children vaccinated
Laryngitis and tracheitis
Caused by parainfluenza, influenza and adenovirus
Burning pain in larynx
Obstructed easily in children
Bronchitis and Bronchiolitis
Viral causes - coronavirus, rhinovirus Smoking related atypical pathogens e.g pneumoniae Secondary infections 75% caused by RSV
Respiratory syncytial virus
Mechanism
Signs in infants
Aerosol spread Large fused cells created Outbreak in winter causes 75% of bronchitis Cyanosis, cough, Rapid RR, pneumonia Some antivirals are used - ribavirin Some antigens on surface change seasonally therefore definite cure is hard to come across
Influenza virus
Transmission
Mechanisms
Aerosol droplet
Initial infection involves attachment of virus to silica acid receptors on epithelial cells via viral HA protein
1-3 days - liberated cytokines result in systemic chills, malaise, fever and muscle aches, runny nose and cough
1 week recovery
Some develop pneumonia and bronchitis
Secondary invaders can cause lethal infections: pneumococci, staph
Influenza structure
Two surface glycoproteins
HA haemaglutinin
NA neuraminidase
HA
types
mechanism
16 avian and mammalian
only 3 human adapted
adheres to sialylated surface receptors and internalisation
HA binds silica acid receptors on epithelial cell surface
major source of antigenic variation
NA
type
mechanism
9 known serotypes and 2 human adapted
neuraminidase and M2 proton ion channel- involved in release from the cell into the resp tract..
Three types of influenza
A - yearly epidemics and occasional serious worldwide - reservoirs in birds and pigs
B - yearly epidemic
C - minor resp illness
Antigenic drift
Small point mutations in H antigen and N antigen which accumulate in popn
Result in new variant viruses which reinfect
Mutations occur in antigenic parts of molecule to prevent antibody binding
Flu vaccines
Strains grown in hen eggs
contain one H3N2, H1N1 and one B strain
Don’t cover pandemics as they come from unexpected strain
Antigenic shift
Less common
Major shift in viral composition
Gene reassortment –>. new HA and NA types
Antigenic shift mechanism
Infection of human animal with human and other influenza virus
Reassortment of genes due to recombination with existing human virus
Spread through immunologically naïve popn
pandemic
