7 Evolution and Emergence of New Viruses Flashcards
Q: Why do viruses evolve so fast? (3)
A: Replicate Fast
Replicate in Large Numbers
High Mutation Rate
*Q: What is a quasispecies (in terms of HIV)? (2)
A: Within a single infected person, you will get HIV genomes which are slightly different because they evolve while they are in the host
=group of viruses related by similar mutations competing within a highly mutagenic environment
Q: What may a virus encounter during replication? Result?
A: Bottlenecks (limiting conditions)-> only one or two of the quasispecies genomes will make it through -> create a whole new quasispecies in another host
Some mutations will improve viral replication and some will emerge to be more predominant than others
*Q: What has relative fitness got to do with drug resistance?
A: could gain a mutation which makes it resistant to a certain drug -> but in doing so could become crippled and no longer be able to replicate and therefore not pass on resistance gene
*Q: What would monotherapy of HIV result in? How would we prevent this? Today?
A: proliferation of a resistant population of HIV (just needs a single mutation to do this)
give a combination of antiviral drugs that target different parts of the HIV life cycle eg protease inhibitors
for a virus to be resistant, it would need 5 or so simultaneous mutations which is unlikely
use HAART
*Q: What is antigenic drift? solution for flu virus?
A: process of antibodies driving evolutionary change over time
vaccine is updated every year to best represent the circulating strains
*Q: Describe antibodies as a selection pressure for evolution. (3)
A: If a person is infected with a virus for which the patient already has antibodies for HA, then the person is immune and protected
BUT, if the person infected has a subneutralising amount of antibody - the virus will replicate in that person and only the fittest viruses survive - ones which change their spike proteins
(antibodies target specific aa sequence on virus so if that sequence were to change-> resistant and become the dominant strain)
*Q: What do rhinoviruses not show? Result?
A: don’t show antigenic drift -> undergo evolutionary expansion but all continue to circulate at the same time
likely to catch many of them in your lifetime = difficult to treat
*Q: How do new viruses emerge? (5)
A: Zoonosis = from animals (adapted to become human viruses)
- Genetic Variation (would require some level of)
- Increased Exposure - travel or world population (often caused by)
- Increased Exposure - spread of vector
- New Discoveries
Q: What are the global influences of emerging infections? (7)
A: -Environmental modifications/demographics
- World population
- Climate change
- Travel
- Farming practices; monocultures
- Immunosuppressed humans
- Medical progress
*Q: What are arboviruses? Example of virus type? 4 examples. Vector? Concern?
A: class of viruses transmitted to humans by arthropods such as mosquitoes and ticks
flaviviruses - single strand positive-sense RNA genomes
- Yellow Fever
- Dengue
- West Nile
- Chikingunya
Mosquito host (replicate within the mosquito) -global warming leads to an increase in the global distribution of mosquitoes
*Q: What’s the vector of the West Nile Virus? Host? Type of virus? causes?
A: Culex tarsalis (mosquito)
bird and mosquito virus that can occasionally affect humans and horses (replicate in us and cause death)
Belongs to Japanese encephalitis group of flaviviruses - cause disease by going to the brain
Q: What is a dead end host? example?
A: With some of these arboviruses, humans and horses are dead end hosts - it doesn’t spread any further
*Q: Describe the outbreak of West Nile Virus was found in New York. RT-PCR showed? Why does it still remain today?
A: hot summers day with lots of mosquitoes in NY
Some elderly people succumbed to a brain disease - crows and birds at the zoo became ill
RT-PCR showed that the virus originated from Israel
in wild bird resevoirs
Q: What is dengue? Describe the process of being infected with it. Serotypes?
A: arbovirus that causes aches and pains usually (first time)
vector= Aedes aegypti mosquito that bites infected human and spreads to someone that’s not (replicates inside mosquito)
4 for dengue virus
