Patterns of viral infection Flashcards
Define tropism.
The predilection of viruses to infect some tissues and not others
What three factors are tropisms based on?
Susceptibility – receptor interactions
Permissivity – ability to use the host cell to complete replication
Accessibility – ability of the virus to reach the tissue
Describe the type of tropism exhibited by HIV.
GP120 on HIV interacts with CD4 on the T cell
It attaches to co-receptors CCR5 and CXCR4
Describe the type of tropism exhibited by Measles.
Measles bind to SLAM on immune cells when they enter the host
They bind to Nectin 4 on airway epithelia when the leave the host
Describe the type of tropism exhibited by Influenza.
Haemagglutinin on influenza binds to sialic acid to gain entry to the cell
Sialic acid is ubiquitous so, in theory, influenza can infect all cells
Once it’s in the endosome, the low endosomal pH allows a massive conformational change that is required for the virus to fuse with the endosome membrane and uncoat
The cleaving of the protein of the virus is essential for the viral genome to gain access to the host cell genetic material
So influenza can only infect cells that have the necessary proteases to cleave the protein
The fluid that lines our lungs have these proteases present
How can influenza tropism be changed?
Influenza tropism is extended by mutation of the HA cleavage site
The mutation could change the cleavage site meaning that more proteases, found in other parts of the body, can cleave the protein
At what point does Varicella-Zoster infection become symptomatic?
After the secondary viraemia
What is the classic triad of Rubella?
Eye Abnormalities (e.g. cataracts)
Deafness
Congenital Heart Disease
Describe the latency of Herpes simplex virus.
Herpes simplex virus can remain latent on nerve cells and then become activated in an attack of shingles
The virus then moves end of the neurones and replicates through the skin (forming a cold sore)
Give four examples of oncogenic viruses and the types of cancer that they cause.
HHV8 – Kaposi Sarcoma
HTLV-1 – Leukaemia
Merkel Cell Polyoma Virus – Merkel Cell Polyoma
HPV – Cervical Cancer
What type of cancer do Hepatitis B and C cause?
Hepatocellular Carcinoma
What types of cancer can Epstein-Barr Virus cause?
Burkitt’s Lymphoma
Hodgkin’s Lymphoma
Nasopharyngeal Carcinoma
Give an example of viral load affecting the outcome of an infection.
Second child in a household infected with chicken pox will have a worse infection because they’ll get a large dose from the first child
Give an example of co-infections affecting the outcome of an infection.
HHV8 can cause Kaposi Sarcoma in people who are infected with HIV and hence are immunocompromised
Hepatitis Delta Virus only infects people with Hepatitis B
Give an example of genetic resistance to a viral disease.
Delta 32 mutation causes the formation of a different CCR5 receptor and so these people are naturally resistant to HIV
