Lecture 3 - Viral Pathogenesis Flashcards
What are some important features of viruses?
- non living
- rely on a host cell to replicate
- non-motile
- no metabolism
- obligate parasites
Which two technologies allow us to visualise viruses?
X ray
Electron microscope
What are the two forms of capsid symmetry?
Helical symmetry
Icosahedral
Which viruses types have envelopes?
Helically symmetrical viruses
Some icosahedral viruses
What are the subunits of the capsid called?
Capsomeres
What is the symmetry of influenza virus?
Helical
What is the symmetry of adenoviruses?
Icosahedral
What is the symmetry of mumps?
Helical
What is the symmetry of herpes virus?
Icosahedral
What is the symmetry of papillomavirus?
Icosahedral
What is the symmetry of poxviruses?
Complex symmetry
All helically symmetrical viruses have a … genome
RNA
Describe how viruses gain access to cells
- Molecules (RECEPTOR BINDING PROTEIN) on the surface of the virus binds to the host’s receptor
- RME or / fusion of envelope with host cell
What determines the tropisms of viruses for cells, tissues, species etc.
- Receptor Binding Proteins
- Enzymes released by host cells (think Tryptase clara)
- Temperature
- Ability to get ‘free ride’ by replicating inside certain cells
What happens once the virus has penetrated the host cell?
Uncoating of the capsid to reveal the genome
What are the ways that a virus can leave the host cell?
1/ LYSIS: Non-enveloped: build up, lyse the cell
2/ EXOCYTOSIS: enveloped viruses, from plasma membrane / golgi
Which is the most common route of entry into the human body for viruses?
Mucosal epithelium
What are the defence mechanisms of the respiratory tracts?
Mucous Ciliated elevator in the trachea Tears Alveolar macrophages Surfactant
Which viruses infect the respiratory tract and remain localised?
Rhinovirus
RSV
Influenza
Which viruses invade via the respiratory tract and then invade further?
Measles
Mumps
Rubella
How does Herpes invade?
To where does it then spread?
Via the oro-pharynx
It remains localised
How does Rotavirus invade?
To where does it then spread?
Invades via the oro-pharynx
Then goes further –> enteritis
How does HIV invade?
Rectal route
What are the defences of the alimentary tract?
Mucous
Acid and Bile
Describe the pathogenesis of mumps
- Entry via respiratory tract
- Primary colonisation of cells of the URT
- Systemic infection of many organs (Sialic acid receptor)
- Mild meningitis (common)
- Encephalitis (uncommon)
- Salivary gland involvement
What is the receptor that mumps virus uses to spread to many organs all over the body?
Sialic acid
What does optimal temperature of replication affect?
The spread of the virus
eg. Rhinovirus needs a slightly cooler temperature, thus it remains localised in the nose
How do viruses usually access the blood?
Via lymph nodes
Why is the blood hostile for viruses?
- Inhibitors
- Antibodies
- Phagocytes
What is it called when there is virus in the blood?
Viremia
What is the difference between primary and secondary viremia?
Primary: low numbers, before amplification in the liver and spleen
Secondary: high numbers, after replication
What are some examples of viruses that spread round the body via the nervous system?
Rabies
Poliovirus:
- not part of its normal pathogenesis, however
Varicella zoster
Describe the pathogenesis of varicella zoster
- Infection of conjuntiva
- Primary virema
- Amplification
- Secondary viremia
- Infection of skin, vesicular rash
- Migration of the virus up the regional dorsal root ganglion
- Latency period
- Immuno-suppression –> Shingles
