Viral Pathogenesis Flashcards
Why can’t viruses infect the outer layer of skin?
Because skin’s outer layer is keratinous so the cells are essentially dead - viruses can’t infect dead cells
Which viruses infect the respiratory system and remain localised?
rhinovirus, respiratory syncitial virus, influenza virus
Which viruses infect the respiratory system but spread systemically?
mumps, measels, rubella, varicella-zoster
What are the most common viral causes of upper respiratory tract infections?
rhinovirus, coronavirus, adenovirus
What is the most common viral cause of pharyngitis?
adenovirus
What is the most common viral cause of croup?
parainfluenza
What is the most common viral cause of bronchiolitis?
respiratory syncitial virus, parainfluenza 3
What is the most common viral cause of pneumonia?
respiratory syncitial virus, parainfluenza 3, influenza virus, adenovirus
What is the cytopathic effect of respiratory syncitial virus?
Giant cells
What are koplick spots?
Spots on the inside of the mouth in measles - where lymphocytes come in to fight the virus
How does the measles virus get from the respiratory tract to a systemic infection?
By infecting local macrophages, lymphocytes and dendritic cells which then drain to the lymph nodes where they amplify and then enter circulation
How is measles transmitted to another person?
Because it returns to the epithelium of the lungs and mouth and is then breathed out (not coughed out)
Why does measles cause transient immunosuppresion?
Because it replicates in cells of the immune system
What kind of viruses enter via the alimentary tract?
Icosahedral viruses without an envelope and possibly multiple capsids - to have the best defence against the many barriers to infection
What virus stays local in the alimentary tract?
rotavirus
What viruses gain entry via the alimentary tract and then spread systemically?
poliovirus, hepatitis A virus
How do viruses gain entry to the alimentary tract if they don’t have receptors for the epithelial cells?
By a breach of the epithelial surface e.g. abrasions in rectum can lead to HIV and hepatitis B infections
How does rotavirus cause diarrhoea?
By infecting and destroying enterocytes which prevents them from absorbing water - and also by encoding for a protein NSP4 which acts like a cholera toxin to increase fluid loss
What happens when infected with an enterovirus?
The virus enters via aerosol or ingestion, then replicates in the oropharynx and is then ingested and replicates in the peyer’s patches, then spread to the circulation to cause primeria viremia and then spreads to a tissue to cause secondary viremia e.g. meninges, CNS, skin, muscle
What are the two types of viremia?
Where the virus is free in the plasma or where the virus is associated with a cell
What happens in primary and secondary viremia?
In primary viremia there is the initial infection in the blood only in a small amount, in secondary viremia the virus replicates in a target organ and then re-enters the blood at a larger amount
What happens if smallpox infects the foetus?
It will cause death of the foetus
What happens if rubella infects the foetus?
Will cause developmental abnormalities
How does infection at birth occur?
Through an infected birth canal, faecal contamination during birth or viremia
Why do certain viruses infect only certain species/tissues?
availability of receptors for the virus
Why does the rhinovirus only cause upper respiratory tract infections?
Requires a certain temperature to replicate only available in the upper airways
What virus has stability in extreme pH?
rotavirus
How do HIV and measles access many tissues?
By replicating in macrophages and lymphocytes
Why is it important whether the virus exits the cell at the apical or basolateral surface?
Viruses that exit at the apical surface will find it more difficult to infect deeper tissues
What enzyme does the influenza virus require?
tryptase Clara secreted by cells in the large airways
How do viruses cause disease?
Either by direct action of virus or as a consequence of the immune response
How does poliovirus cause paralysis?
By killing neurons in the spinal cord due to viral replication
How does rhinovirus cause loss of cell function?
Causes cilial stasis
What cytokines cause fever?
IL-1 and TNF
How does dengue fever cause shock?
By internalising virus-Ab complexes into the macrophage which enhances the infection
What is the rash in measles due to?
Accumulation of CD4 T cells
How does RSV cause bronchiolitis?
By inducing cytokines that recruit eosionophils
How does hepatitis B cause liver damage?
Leads to our own CD8 T cells killing hepatocytes
What are the symptoms of liver damage?
Yellow eyes and skin
What happens in molecular mimicry?
After the virus is gone antibodies attack own proteins which are similar to the virus
What viruses lead to immunosuprresion?
HIV and measles
What is the result of immunosuppresion?
Susceptible to secondary infections
