rapid evolution in viruses

Question 1

Why do viruses evolve so rapidly?

Answer 1

3 main reasons:

1. Fast generation time – Viruses can evolve in hours, while humans take years.
2. High mutation rates – RNA viruses have no proofreading mechanisms.
3. Natural selection – New variants can evade immune responses, like antibodies.

Question 2

How does fast generation time contribute to rapid evolution in viruses?

Answer 2

Viruses have a short generation time (sometimes less than an hour), allowing them to evolve much faster than organisms with longer generation times, like humans (which is about 25 years).

Question 3

How do high mutation rates contribute to rapid evolution in viruses?

Answer 3

RNA viruses lack proofreading during replication, leading to high mutation rates. This increases genetic variation and the potential for new viral strains.

Question 4

How does natural selection drive viral evolution?

Answer 4

Natural selection acts on viral variations. New variants may evade immune detection (e.g., antibodies), allowing them to survive and replicate, which speeds up viral evolution.

Question 5

How does the mutation rate affect Influenza virus evolution?

Answer 5

• Influenza is an RNA virus with a high mutation rate due to lack of proofreading by RNA replicase.
• The genome has 8 segments, so new strains can arise from mixing two different strains in a host cell.
• Antigens (like haemagglutinin) can change, creating new strains (e.g., H1N1, H3N2), causing pandemics.

Question 6

Why do influenza strains need frequent vaccination updates?

Answer 6

Influenza strains evolve quickly due to antigen changes (e.g., haemagglutinin), leading to new strains each year. This is why annual vaccinations are necessary to keep up with evolving strains.

Question 7

How does the mutation rate affect HIV virus evolution?

Answer 7

• HIV has one of the highest mutation rates due to reverse transcriptase (which doesn’t proofread) and host enzymes (e.g., cytidine deaminase).
• This high mutation rate generates many different strains within an infected person.
• HIV can mutate to avoid immune detection and develop resistance to drugs.

Question 8

How does HIV evolve to escape the immune system?

Answer 8

Mutations in the env gene (which codes for the surface protein) allow HIV to bind to and infect different cell types, helping it evade immune responses and make infections chronic.

Question 9

Why is combination therapy important for treating HIV?

Answer 9

HIV evolves resistance to antiretroviral drugs quickly. A combination of drugs is necessary to combat this rapid mutation and effectively treat the infection.