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Ecology and Environment > Lecture Twenty-One - Host-Parasite Dynamics and Disease > Flashcards

Lecture Twenty-One - Host-Parasite Dynamics and Disease Flashcards

1
Q

Describe microparasites.

A
  • Small
  • Usually intracellular
  • Exist in vast numbers within hosts
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2
Q

What are the smallest parasites called?

A

Microparasites

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3
Q

Give three kinds of micro parasite.

A
  • Measles (virus)
  • Typhoid (bacterium)
  • Plasmodium (protozoa)
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4
Q

What is prevalence?

A

The number of hosts parasitised at a particular time.

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5
Q

Describe macroparasites.

A
  • Grow on or in hosts

- Create infective stages which transmit within hosts

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6
Q

Give four macroparasites.

A
  • Tapeworms
  • Ticks
  • Common dodder (in plants)
  • Mistletoe
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7
Q

What are some differences between the habitat of a free-living organism and a parasite’s habitat?

A
  • Biology of the host can influence its susceptibility to the habitat, e.g. immune reactions, evolution.
  • Host has its own population dynamics.
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8
Q

How do parasite-host models differ from predator-prey models?

A
  • Contact between hosts results in transition between parasites; parasites depend on movement patterns of hosts themselves, rather than direct contact between predator and prey.
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9
Q

Give a species that requires a vector.

A

Plasmodium falciparum, causing malaria (requires mosquitos)

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10
Q

Give the three types of host in the host-parasite model.

A
  • Susceptible hosts
  • Infected hosts
  • Resistant hosts
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11
Q

What are susceptible hosts?

A

Hosts that can pick up the infection.

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12
Q

What are resistant hosts?

A

Following infection, hosts become resistant and are no longer susceptible.

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13
Q

Give the equation for the change in the number of susceptible hosts over time.

A

dS/dt = b(S + I + R) - dS - BSI

B = parameter for rate of transition.

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14
Q

What is Beta in the parasite-host model?

A

Probability that contact between susceptible and infected host results in infection.

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15
Q

Give the equation for the change of the number of infected individuals over time.

A

dI/dt = BSI - dI - AI

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16
Q

In the parasite-host model, what is Alpha?

A

Declines via natural and parasite-induced mortality.

17
Q

Give the equation for host-parasite model that takes into account the number of resistant individuals.

A

dI/dt = BSI - dI - AI - GI

18
Q

In the host-parasite model, what is gamma?

A

The number of infected hosts becoming resistant.

19
Q

Give the equation for the change in resistant individuals over time.

A

dR/dt = -dR + GI

20
Q

What is the basic reproductive rate of a parasite?

A

The number of new infections arising from one infection.

21
Q

What is R0 representative of?

A

The basic reproductive rate.

22
Q

What is the basic reproductive rate determined by?

A

1) The number of susceptible individuals.
2) The transmission parameter.
3) The length of time that each infected individual remains contagious.

23
Q

What is the value of R0 for

a) Measles?
b) Rubella?
c) Smallpox?
d) HIV/AIDS?
e) Ebola?

A

a) Measles = 12-18
b) Rubella = 5-7
c) Smallpox = 5-7
d) HIV/AIDS = 2-5
e) Ebola = 1.5-2.5

24
Q

Which disease has the

a) Larges R0?
b) Smallest R0?

A

a) Largest R0 = Measles

b) Smallest R0 = Ebola

25
Q

When does disease spread?

A

If R0 is greater than 1.

26
Q

What is meant by low transmission threshold?

A

Does not require many individuals to be able to spread.

27
Q

If a parasite has a large Beta, what does this signify?

A

That it is highly infectious

28
Q

If a parasite has a large L, what does this signify?

A

It has a long period of infectiousness

29
Q

What do species with a high transmission threshold require to persist?

A

A large host population

30
Q

Give a disease with a high transmission threshold.

A

Measles (Morbillivirus)

31
Q

What can be said about the epidemic curve for a species with high R0?

A
  • Faster growth

- Faster removal of Susceptibles

32
Q

What population number does Measles require to clear the number of susceptibles?

A

300,000

33
Q

What is the control of disease outbreak dependent on?

A

Movement of infected individuals.

34
Q

Give the equation for the minimum proportion of population to immunise.

A

pc = 1 - (1 / R0)

35
Q

What is pc?

A

The minimum proportion of population to immunise.

36
Q

For measles, approximately what percentage of the population needs to be immunised to eradicate the disease?

A

Approx 93%

37
Q

Why might parasites or pathogens have an R0 of less than 1?

A
  • Not adapted to the host
  • Due to control measures, e.g. vaccination
  • Environmental conditions of host dynamics do not allow spread.
38
Q

What allowed HIV to spread so readily in Africa?

A

Changes to partner acquisition.

39
Q

Give a species with cyclic population dynamics, and the parasite likely to cause this cyclic pattern.

A

Red grouse, caused by Nematode worms.

Ecology and Environment (22 decks)

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