Evolution

Question 1

Methods of control of malaria

Answer 1

Vector Control: killing vector (mosquito control)
Drug: killing parasite
Decreasing contact between humans and vector

Question 2

drug treatmetns in humans leads to

Answer 2

drug resistance in parasites

Question 3

why is there drug resistance in parasites

Answer 3

1. Genetic variation in parasite sensitivity to drugs
2. Under drug pressure less sensitiv/more resistance strains survive better and remove competitiors

Question 4

insecticide resistance

Answer 4

treatment with organophoshate between 1968-1990 because of resistance allele

Question 5

why are antibiotics a major force of selection for bacteria

Answer 5

• susceptible genotypes killed by antibiotics
• resistant genotypes survive

Question 6

Plasmids and Horizontal Gene Transfer

Answer 6

resistance genes can be transferred among bacterial cells via extra-chromosomal loops of DNA called plasmids

Question 7

Life Cycle of HIV

Answer 7

1. HIV is a dsRNA retrovirus
2. infects hosts CD$ helper T cells
3. Viral enzyme (reverse transcriptase) turns RNA into DNA
4. Embeds genome into host DNA
5. Viral Genes transcribed and translated by host machinary
6. New virus buds out of host cells

Question 8

AZT resistance in HIV

Answer 8

• AZT drug binds to and inactivates HIV enzyme
• new mutant enzyme arose with binding site that was resistant to AZT

Question 9

why does HIC evolve so fast

Answer 9

• massive population size
• short generation time
• high mutation rate

Question 10

solutions for drug resistance

Answer 10

1. Higher dose
2. earlier treatment
3. combinations of drugs

Question 11

virulence

Answer 11

• disease severity as assessed by reductions in host fitness due to infection
• interpeted as the additional mortaility rate that a pathogen imposes on an infected individual

Question 12

Conventional Wisdom

not true

Answer 12

pathogens that harm their hosts therby harm themselves

Question 13

conventional wisom predictions

Answer 13

• over time, the coevolution of pathogens and their host will lead to a mutualistic association
• evolution would eventully lead to avirulance
• instances of highly virulent pathogens are cases where host-pathogen relationship is recent**

** applies to ebola and bird flu

Question 14

challenges to conventional wisdom

Answer 14

tuberculosis (has been around sincee 3000 BCE)
Myxoma: (rabbit disease) over time, it adapted to an intermediate vrulence which cannot be explained

• biggest challenge

Question 15

tradeoff hypothesis

Answer 15

• level of virulence is consequence of pathogen replication in host => cost of replication
• Benefit: pathogen replication is required for transmission between hosts
• Replication rate of pathogen and virulence evolves to maximize overall tranmission and spread

Question 16

Model of virulence evolution
(equation)

Answer 16

R0=T(r) x D(r)
T(r)= # of new infections/ day (transmission rate)
D(r)= # days infection lasts (duration)
increased r (replication rate) increases transmission rate but decreases duration

pathogen cannot increase infection without decreasing duration

Question 17

optimizing virulence
most virulent=x, least virulent= y

Answer 17

most virulence= high transmission but kill host quickly
least virulent= long infections but transmit poorly
**Prediction: ** strains of intermediate virulence will increase in frequency

this prediction was upheld in myxoma

Question 18

Modes of Disease transmission

Answer 18

direct host to host transmission
Vector transmission

Question 19

direct host to host transmission

Answer 19

hosts must be mobile and functioning relatively well in order to transmit disease
prediciton low replication rate and low virulence

Question 20

vector transmission

Answer 20

host do not need to be mobile to transmit
prediction high replication and high virulence

Question 21

virulence evolution

Answer 21

• virulance is unvaoidable consequence of parasite transmission
• parasites need to exploit hosts to transit to new hosts
• increase in transmission due to replication = cost of increase in virulence

transmission is the benefit, virulence is cost

Question 22

benefit-cost of parasites is maximized

Answer 22

at intermediate levels
at intermediate replication rate, marginal beneft = marginal cost

for single parasite

Question 23

at low replication rates
at high replication rates
marginal benefit vs cost

Answer 23

marginal benefit > marginal cost (selection for increasing replication
marginal benefit < marginal cost (selection for decreasing replication)

for single parasite

Question 24

Multiple infections

Answer 24

favour evolution of more virulent parasites

Question 25

tragedy of the commons

Answer 25

strains compete for same resource
more virulent strain has higher relative transmission