Infectious diseases

Question 1

Charlton Endogenous Parasitism

- Dawkins, paradox of the organism (conflict)

Answer 1

Conflict between selfish genes goals and the whole organism. Genes will collaborate to maintain their ‘vehicle’, their only route into future generations - work together

Question 2

The Red Queen theory of the evolution of sex

Answer 2

“now here, you see, it takes all the running you can do to keep in the same place” -Carroll, in Through the Looking Glass
The idea that new and unfamiliar combinations of genes could be presented to parasites, preventing them from preying on the organism. The parasites evolve counter-adaptations to these new combinations, leading to the organism needing more advanced adaptations…. co-evolution, arms race

Question 3

Like the host and parasite arms race of co-evolution:

Answer 3

Replicating somatic lineages are in competition with the organism: lineages will tend to evolve into ‘free-riders’, become more parasitic, exploit advantages of the intra-organismal environment without paying the costs of cooperation. Can even kill it in extreme cases

Question 4

EP as a mechanism for senescence

Answer 4

Accumulation of free-riding = reduced cooperation = dysregulation, internal environment is a challenge to survival of the organism

Question 5

Senescence at the level of the genes

Answer 5

Caused by natural selection rather than the accumulation of random mutations. Success = escaping somatic duties…
However, organisms tend to be killed by reproducing, evolving competitors than by natural causes. More relevant to the Red Queen hypothesis

Question 6

Ewald (1993) why is virulence varied?

Answer 6

1- mode of transmission
2- ability to survive outside the host
3- effect of human behaviour

Question 7

1 - mode of transmission

Answer 7

If immobility of the host impairs transmission, virulence should be mild
If it doesn’t, virulence should be rapid
In rhinovirus, movement is critical to spreading the infection, so V remains mild
In a disease with a vector, V can remain high because it doesn’t require host mobility

Question 8

2 - ability to survive outside of host

Answer 8

Are more injurious and cause more mortality. No limit to how bad they can become

Question 9

3- effect of human behaviour

Answer 9

Some activities create cultural vectors. E.g. hospitals, attendants inadvertently carry pathogens on their hands, high risk of infecting newborns. 1 in 20 US patients acquire an infection during a hospital stay

Question 10

Changing the course of virulence

Answer 10

Invest in interventions: to reduce sexual transmission (already occurring, we are seeing an unplanned experiment between those engaging in risky sexual behaviour and those practising safer sex, in the disease of HIV), improve hand-washing practises in hospitals, and improve water purification, mosquito-proof houses