evolution and emergence of new viruses Flashcards
why do viruses evolve fast?
- replicate fast
- replicate in high numbers
- high mutation rate
what happens when a bottle neck happens?
- only one or two of the genomes will make it through
how to prevent drug resistance in HIV drugs?
- must give a combination of antiviral drugs because that means that more simultaneous mutations are needed
- this is unlikely
- Error rate is roughly 1 per 10,000 nucleotides and as each genome is roughly
10,000 nucleotides long,
therefore multiple drugs are needed
how do antibodies also exert selection pressure on viruses ?
- if the person has enough antibodies to kill the virus then they are fine
- if the person only has enough antibodies to neutralise the amount of antibody the virus will replicate but only the fittest will survive
- this is called antigenic drift
- shown in influenza
how might new viruses emerge?
- zoonosis
- genetic variation
- increased exposure
- new discoveries
what are arboviruses?
- A class of viruses transmitted to humans by arthropods such as mosquitoes and ticks.
what are examples of arboviruses?
- yellow fever
- dengue
- west nile
- Chikingunya
what are flaviviruses?
- single strand positive-sense RNA genomes
what is west nile virus?
- belongs to a japanese group of flaviviruses
- it causes disease by going to the brain
how do the effects of dengue fever change?
- first time you get it you are not very sick
- second time with the disease you are infected by a new serotype
- the antibodies from before make you more sick
- This is called Antibody Dependent Enhancement of the Infection
what are risk factors for dengue fever?
- Pre-existing anti-dengue antibody
- virus strain
- age
- higher risk in secondary infection
what happens if the dengue virus binds to homologous antibodies?
- these antibodies are a perfect match to the virus
- the viral antigens will bind the antibodies TIGHTLY and stop it from entering the cell
-
what happens if the dengue virus binds to non homologous antibodies?
- If infected by a different viral serotype - the antibodies bind loosely to the antigens but don’t block it
- antibodies can bind to Fc receptors on immune cells
- virus is carried to the immune cells
- this leads to a cytokine storm and dengue haemorrhagic fever
how is SARS transmitted?
- respiratory droplets
how does SARs affect people ?
- elderly people show high mortality
- Patients did not become contagious until quite late into the infection once
they had become symptomatic - this means you can see who has SARs and isolate them
what is a coranovirus?
- positive-sense RNA genome
what are the SARS coronoviruses?
Mammalian = Groups 1 + 2 Avian = Group 3
what is MERS
Coronavirus
- uses zoonosis
what does antigenic drift do?
- it causes the virus to completely change
- Humans live long enough to be re-infected so their antibodies can drive
evolution
