Respiratory Viruses Flashcards
What causes bronchiolitis (viral chest infection of lower respiratory tract)
RSV (respiratory syncytial virus)
Parainfluenza virus
Adenovirus
What causes Croup (laryngotracheobronchitis)
• RSV
• Parainfluenza virus
• Influenza virus
• Measles virus
What does respiratory syncytial virus (RSV) cause
LRTI in young children
• Bronchiolitis
• Usually children under 12 months
• Wheezing, increased respiratory rate. Cyanosis and apnoea in severe cases
Pneumonia
• May be life threatening
URTI in adults
• Common cold
• Elderly may develop pneumonia
Treatment includes
• Supportive management
• Antivirals eg ribivarin – in complicated cases
• IV Immunoglobulin in specific cases
What do coronavirus cause
Second most common cause of common cold (15-20%)
Usually milder infection
• 50% of infection may be asymptomatic
• Exception is SARS CoV, SARS – Cov 2 (Covid-19)
The virus
• RNA virus
• Family Coronaviridae
• Club shaped spikes on surface (crown-like on EM)
Pathogenesis of coronavirus
• After viral entry, initial immune response attracts viral specific T
cells to site of infection
• Infected cells eliminated before virus spreads, leading to recovery
in most people
• In patients who develop severe disease SARS – CoV 2 elicits an
aberrant immune response
What do adenovirus cause
Infections of respiratory tract, the eye, the GIT
• Transmission by droplet and contact
• Incubation period 5-10 days
• Usually causes URTI
• 50% of infections are asymptomatic
• Occasionally severe bronchopneumonia in infants
• May cause whooping cough-like disease.
The virus
• DNA virus
• 47 or more serotypes
Therapy – not available
Laboratory diagnosis
Viral antigen detection by PCR
What does parainfluenza virus cause
• Major cause of croup, bronchiolitis and pneumonia.
• Second to RSV as cause of serious RTI in infants and children
• Four serotypes
• Transmission is by contact or droplet spread
The virus
• RNA virus
• Family Paramyxoviridae
Therapy – none available
Laboratory diagnosis
• PCR antigen detection
What are the two types of influenza virus
A viruses :
• cause outbreaks most years and are the usual cause of epidemics and pandemics
• live and multiply in many different animals and may spread between them
• birds, particularly wildfowl, are the main animal reservoir
B viruses :
• tend to cause less severe disease and smaller outbreaks
• predominantly found in humans
• burden of disease mostly in children
Pathogenesis of influenza virus
• H – allows attachment of virus to respiratory epithelial
cells via receptors
• Virus is transported into cytoplasm in an endosome
• Acid PH in endosome activates/opens an ion channel called M2 protein, allowing H+ ions to enter the virus
• Acidification of the virus is necessary for viral uncoating, an essential step in replication
• N - digests neuraminic acid in respiratory mucus facilitating viral spread
What are the genetic changes in the influenza virus and what does it affect
• Changes in the surface antigens (H and N) result in the flu virus constantly changing
• Antigenic drift: minor changes (natural mutations) in the genes of flu viruses that occur gradually over time
• Antigenic shift: when two or more different strains combine. This abrupt major change results in a new subtype. Immunity from previous flu infections/vaccinations may not protect against the new subtype, potentially leading to a widespread epidemic or pandemic
Types of influenza vaccine
Two main types of vaccine available:
• inactivated – given by injection
• live attenuated – given by nasal application
• None of the flu vaccines can cause clinical influenza in those that can be vaccinated
Trivalent: flu vaccines contain two subtypes of Influenza A and one type B virus Quadrivalent vaccines contain two subtypes of Influenza A and both B virus types
As quadrivalent vaccines contain both lineages of B viruses and therefore may provide better protection against the circulating B strain(s) than trivalent flu vaccines, the live intranasal vaccine offered to children aged 2 years and over is a quadrivalent vaccine
How do covid vaccines work
• Nucleoside-modified messenger RNA vaccine (mRNA) vaccines
targeting the S protein
• mRNA vaccines use the pathogen’s genetic code as the vaccine;
this then exploits the host cells to translate the code and then
make the target spike protein
• The protein then acts as an intracellular antigen to stimulate the
immune response
• mRNA is then normally degraded within a few days
