Microbiology 5- Patterns of virus infection Flashcards
What is viraemia
Virus in the blood
Describe Varicella Zoster Virus chicken pox:
Virus enters the body through the respiratory route
VZV can infect many cell types including peripheral blood mononuclear cells (PMBCs) and skin cells
From the skin site it can infect sensory neurones where it remains latent
Virus can be reactivated when cellular immunity is impaired causing a painful rash at nerve endings - SHINGLES
You only get symptoms after secondary viraemia
Incubation Period: 14 days
What is tropism and what 3 things is it based on
the predilection of viruses to infect certain tissues and not others.
This is based on:
Susceptibility - receptor interactions
Permissivity - ability to use the host cell to complete replication
Accessibility - ability of the virus to reach the tissue
What is the tropism of HIV determined by
Receptor use
Some people have mutation in CCR5 (delta 32) which means they don’t make a proper CCR5 receptor and hence are resistant to HIV
Some people who are exposed and unaffected produce a large amount of chemokine which blocks the use of the co-receptors
You can get a tropism switch during HIV replication - viruses evolve to bind to other receptors (e.g. from CCR5 to CXCR4)
How does measles virus get in and out of cells
H receptor on virus binds to
CD155 (SLAM) on the way IN on immune cells
nectin 4 on the way OUT on airway epithelia
How does influenza infect cells of our body
Fusion of the viral membrane and uncoating can only happen if the protein of the virus has been snipped in two at a particular point
It is only in the fluid that lines our lungs that the right proteases are present.
Viruses mill around until they come into contact with the appropriate proteases which can chop the HA in two and activate the virus.
Define pathogenicity
the ability of a virus to cause disease
Define Virulence
describes the capacity of a virus to cause disease
Examples of acute infection (5)
Influenza Smallpox dengue polio rubella
Examples of persistent viral infections
chronic= papillomaviruses in wart
Latent- Herpes
Explain the oncogentic way papillomavirues work
Papilloviruses encode inhibitors of tumour suppressor p53, E6 and E7 genes - forces cells into S phase
Outcome of infection can vary depending (8)
Viral sequence
Virus load
Host immune repsonse/status
Host co-morbidity
Co-infections
Other medications
Host genetics
Host age/gender
