Evolution and emergence of new viruses Flashcards
Why do viruses evolve quickly?
- Fast replication
- Replicate in large numbers
- High mutation rate
What is a quasispecies?
- Viral genomes within person which are slightly different because evolved
- Some make it through and become drug resistant because genome changes
- Bottlenecks occur every now and then through which only one or two quasispecies genomes make it through
How do you prevent viral drug resistance?
- Must give combo of drugs e.g HIV so must acquire more mutations
- HAART highly active anti retroviral therapy
What is another evolution mechanism?
- Antibodies also select selection pressure
What is antigenic drift?
- antigens gradually change because selections pressure from antibodies
- If person has sub-neutralizing amount of antibody virus replicates and only those who change spike proteins survive
How do new viruses emerge?
- Environmental modification
- Travel
- World population
- Climate change
- Farming practice
- Medical progress
- Immunosuppressed human
- Zoonosis
- Genetic variation
- New discoveries
What are arboviruses?
- class of viruses transmitted to humans by arthropods
- Eg yellow fever, dengue, west nile virus
- Many are flavivirus: single strand positive sense RNA genome
- Flavi- and alphaviruses
What is antibody dependent enhancement of infection?
- antibodies from 1st infection make you more sick
What are the risk factors for dengue hemorrhagic fever?
- Pre existing antibody
- Virus strain
- Age
- Higher risk f secondary infections
- Higher risk in area with 2 or more serotypes circulating simultaneously at high levels (hyperendemic transmission)
What is chikingunya?
- Similiar to dengue fever
- More chronic
What are human viruses from animal sources?
- SARS coronavirus ○ Positive sense RNA genome ○ Bats then civet cats - HIV (primates) - MERS - MERS coronavirus ○ Zoonosis from camels
What are some emerging viruses?
- MERS
○ Limited transmission
○ Diverse clinical signs
○ No vaccine, no antiviral
- H7N9
○ Limited transmission
○ No vaccine but technology to make one
known
○ Antivirals but resistance tolerated
How do new viruses with new properties emerge?
- Recombination of 2 or more viruses
- Due to antigenic drift
- Humans live long enough to be infected with same virus
- E.g swine flu
What is zoonosis?
New viruses that infect humans often cross over from animal reservoirs.
Why does zoonosis not happen very often?
host range barrier.
What is antigenic shift?
new virus spreads rapidly around the world and most often displaces any virus previously circulating.
e.g influenza
What is reassortment?
jumping from species
What is the natural host of the west nile virus?
infection of mosquitoes and birds are the natural host.
What type of virus is norovirus and what does it cause?
small RNA viruses that cause diarrhoea and vomiting.
What does the complement system do?
the complement system punches holes into bacteria
