Blood Bourne Viruses Flashcards
What are capsids?
Protein coating of viral nucleic acids made up of only repeating units
What is a virus?
A small infectious agent that replicates only inside the living cells of other organisms
What are the two symmetries of capsids?
Icosahedral - form an almost spherical structure
Helical - found in RNA viruses that have capsids bound around helical nucleic acid
What is an enveloped virus?
When the nucleic acids and capsid proteins are surrounded by a lipid envelope derived from the host cell or nuclear membranes
What are lipid viruses sensitive to?
Substances that dissolve the lipid membrane
What can be viruses be classified by?
Genetic material
Mode of replication
Structure and symmetry of structural proteins (capsids)
Presence/absence of an envelope
What are the two classifications of DNA viruses?
Double stranded (dd) Single stranded (ss)
Name some dd viruses
Pox virus
Herpes
Adenovirus
How do DNA viruses normally replicate?
In the nucleus of the host cell
Produce a polymerase which reproduces viral DNA
(Viral DNA not normally incorporated into host DNA)
Two classifications of RNA viruses?
Sense (positive)
Antisense (negative)
How do RNA sense (positive) replicate?
RNA may serve directly as mRNA
Translated into structural protein and an RNA-dependent RNA polymerase
How can antisense (negative) viruses replicate?
Contain an RNA-dependent RNA polymerase that transcribes the viral genome into mRNA.
Alternatively, transcribed RNA can act as a template for further viral antisense RNA
What are retroviruses?
Viruses which possess ss+ RNA that cannot act as mRNA
Transcribe into DNA by reverse transcriptase and incorporated into host DNA
Subsequent transcription to make mRNA and viral genomic RNA is under control of host transcriptase enzymes
Classify HIV
Spherical enveloped RNA retrovirus
How does HIV replicate?
Uses reverse transcriptase to produce DNA copy from viral RNA
This is incorporated into the host nucleus to become a template for further viral RNA
What are the two types of HIV and which is most common?
HIV-1 most common
HIV-2 found mainly in west Africa
Which type of HIV is less virulent?
HIV-2
How is HIV transmitted?
Parenterally
Sexually
How is HIV spread in developing countries?
Heterogenous sex
Unscreened transfusions
Contaminated medical equipment
Which cells does HIV infect?
Those with a CD4 receptor
So T cells and macrophages
Pathogenesis of HIV?
Binds to host cells
Virus and cell fuse
This releases enzymes for reverse transcription and integration into host genome (using integrase)
T cell itself is activated by fighting an infection
Causes cellular transcription factors to be present which allows HIV to be actively produced
Mature in bud at host cell plasma membrane (long chains of proteins come together)
Buds off to infect another cell
Protein chains in new viral particle cut by protease into individual proteins which combine to make a working virus
Why is it difficult to design treatments for HIV?
Reverse transcription of HIV viral RNA to DNA is error prone so has a high mutation rate
What are the aims of management of HIV?
Minimise replication
Prevent emergence of resistant virus
Reconstitute immune response
What types of drugs are used in the management of HIV?
Non-nucleoside reverse transcriptase inhibitors (NNRTIs) Nucleoside RTIs (NRTIs) Protease inhibitors Fusion inhibitors Integrase inhibitors Co-receptor/enthusiasm inhibitors
How can transmission from mother to child be prevented?
Administration of HAART
C-section
Avoid breastfeeding
Principles of infection prevention of HIV?
Avoid high risk partners Avoid unprotected sex Blood products should be screened Free needle exchange programmes Anti-retrovirus prophylaxis for needle-stick injuries
Classify hep B
Hepadnavirus
Small
Enveloped
dd DNA
What does the DNA in HBV code for?
HBsAg, HBcAg, HBcAg - 3 surface antigens
Large active polymerase protein
Transactivator protein
What percentage of the world’s population have been infected with HBV? Proportion who are chronic carriers?
Third of the population has been infecte
5% are chronic carriers
What percentage of those who carry HBV will go on to develop liver disease?
25%
Mechanisms of infection of HBV?
Parenteral
Sexual
Congenital
Incubation period of HBV before development of acute hepatitis?
Up to 6 months
Complications of chronic hepatitis?
Cirrhosis
Hepatocellular carcinoma
Symptoms of HBV?
Fever
Malaise
Jaundice
Raised ALTs
Main treatment of HBV?
Peglycated interferon (IFN) is the best for sustained suppression without drug resistance Can also use a nucleoside inhibitor to reduce viral load but resistance can emerge
What can antiviral suppression of HBV for 2-5 years result in?
Ever say of hepatic fibrosis and prevents cirrhosis
If cirrhosis is established, can improve liver function and reduce cancer risk
Prevention of HBV?
Immunisation
Vaccine and immunoglobulin to neonates of infected mothers
Needle exchange programmes
Sexual health education
