0522 - Retro and Arboviruses Flashcards
HIV can integrate itself into the human genome. Is this ability unique to HIV?
No - there are 100,000 retroviruses that have integrated themselves into the human genome (5-8% of the genome). Some of these, endogenous retroviruses (check definition) have reached the stage where they no longer spread, just hang out in the genome.
What is a retrovirus? How can it integrate itself into the host genome?
All retroviruses can transcribe RNA into DNA (hence why retro). Once the DNA is circular and double-stranded, it can be integrated into the host genome. At this point it behaves like normal DNA for protein synthesis, and will be in the genome for all daughter cells.
How does reverse transcription work (steps)? What are its drawbacks?
Reverse transcriptase:
- Makes ssDNA from RNA template
- Destroys RNA template
- Makes second strand of DNA from DNA template.
- It does not amplify (so one RNA = one dsDNA) or proof-read the gene.
- Very high mutation rate.
What is a viral quasispecies? Use HIV as an example
A group of viruses with high and constantly evolving sequence diversity. The genome mutates too rapidly to be able to sequence it, think of it as a ‘swarm’ of genomes that mutates over time.
HIV is a quasispecies because of it’s poor genetic fidelity. It evolves, morphs and changes extremely rapidly, so that a person doesn’t have a single, genetically distinct virus, but a population that changes over time.
What are the molecular events that cause the genetic diversity seen in HIV?
Lack of ability to proofread the gene with 3’-5’ exonuclease.
Ease of recombination between 2 viruses in same cell
Rapid replication and high viral load in infective tissues
Immune selection of variants.
Why is it hard to assign viral aetiology to human disease? (KEY EXAM CONCEPT!!!!)
Viruses are often proposed as a cause, but sensitive detection (e.g. PCR) is prone to contamination and error.
Ensure adequate sample sizes and strong statistics, appropriate controls, detection by more than 1 method, independent verification. Association does not equal causation.
What is the significance of arthropod vectors and bird/animal reservoirs in arbovirus infections?
Arthropod-borne viruses. Humans are incidental/dead end hosts, but may be human. The vectors and reservoirs provide a means of preventing or combating the spread of disease. Vector control, and removal from reservoirs, can be very effective in removing the disease.
What are the main arbovirus threats to human health in the local region and in Australia?
Australia - Murray Valley Encephalitis, Dengue,
Ross River, Barmah forest viruses.
Murray valley big one for local region.
