Evolution

Question 1

What is a viral quasi-species?

Answer 1

population of related viruses in a host, which have minimal mutations, and therefore not strictly identical copies

Question 2

What does the R0 (R-naught) number mean?

Answer 2

Basic reproductive number is number of secondary infections that can arise in a large population of susceptible host, from a single infected individual during its life span

Question 3

What factors are part of the R0 (R-naught) equation?

Answer 3

R0 =

• probability of infection e.g mode of transmission, respiratory is easier than contact
• average contact between infected and non-infected. i.e do people stay at home when they are infected
• duration of infectivity

Question 4

What factors are part of the R0 (R-naught) equation?

Answer 4

R0 =

• probability of infection e.g mode of transmission, respiratory is easier than contact
• average contact between infected and non-infected. i.e do people stay at home when they are infected
• duration of infectivity

Question 5

What are benefits of drawbacks of viral virulence?

Answer 5

Causing disease is a way to ensure transmissibility e.g respiratory symptoms

However, can make hosts die fast, reducing exposure to the uninfected. And if debilitating, may make people stay at home in bed, reducing exposure to further hosts

Most viruses have a balance between virulence. Enough to ensure disease and transmission ,but not enough to kill hosts

Question 6

What are the “r” and “K” replication strategies for viruses?

Answer 6

r-replication - virus produces large numbers of progeny particles, which ensures some will survive

K-replication - lower reproductive output, but better competition for resources

Question 7

Viral mutations can help escape immune system/ treatment

What are drawbacks of this?

Answer 7

Can make virus less fit - many mutations are detrimental

Can cause lethal mutagenesis - population driven to extinction, because less fit mutations mean virus can no longer survive

Question 8

What is segmented viral nucleic acid?

Answer 8

viral genome sometimes split into separate parts - segmented

non-segmented - whole viral genome consists of one piece of RNA. e.g HSV has one linear dsDNA molecule

segmented - enables virus to generate reassortants in co-infected cells. RNA molecules of different virus strains mixed or reshuffled together. e.g influenza A has 8 ssRNA segments

Segmented viruses are all RNA viruses

Question 9

What are the benefits of segmentation of viral genome?

Answer 9

Ability to reassort genes means that virus can mutant and adapt easier