Transmission and Virulence

Question 1

What are hosts better able to do?

Answer 1

Hosts are better able to resist and tolerate parasites.

Question 2

What are parasites better able to do?

Answer 2

Parasites are better able to feed and reproduce.

Question 3

What is transmission?

Answer 3

Transmission is the spread of a parasite to a host.

Question 4

What is virulence?

Answer 4

Virulence is the potential of a parasite to cause harm to a host.

Question 5

Describe the relationship between transmission rate and virulence.

Answer 5

THE HIGHER THE TRANSMISSION RATE, THE GREATER THE VIRULENCE.

Question 6

Give two methods by which a parasite can be passed on from host to host.

Answer 6

1. Vertical – from parent to offspring e.g. HIV or Rubella

2. Horizontal – from one generation to another

Question 7

When are transmission rates greatest?

Answer 7

• Overcrowding of hosts, such as in places with high population density.
• A means of transmission, such as the presence of vectors, e.g. mosquitoes, or water for water borne parasite, e.g. cholera.

Question 8

Give 4 methods of transmission.

Answer 8

1. Direct skin contact e.g. herpes simplex virus (cold sores)
2. Respiratory route e.g. flu virus
3. Sexual contact e.g. HIV
4. Close proximity e.g. Fleas

Question 9

What do most successful parasites have?

Answer 9

The most successful parasites have efficient modes of transmission and rapid rates of evolution.

Question 10

What are parasites that can maximise transmission favoured by?

Answer 10

natural selection.

Question 11

Explain the extended phenotype.

Answer 11

The most successful parasites have adapted means to exploit and change host behaviour in order to increase transmission rates.
In effect the parasite makes the host behave in such a way that transmission of the disease increases.

Question 12

Give examples of host behaviours may be altered to increase transmission rates. (5)

Answer 12

	Foraging 
	Movement 
	Sexual Behaviour 
	Habitat Choice 
	Anti-predator Behaviour