2.5c Transmission and virulence

Question 1

Transmission definition

Answer 1

Transmission is the spread of a parasite to a host.

Question 2

Virulence

Answer 2

Virulence is the harm caused to a host species by a parasite.

Question 3

Transmission of ectoparasites

Answer 3

Ectoparasites are generally transmitted through direct contact or by consumption of intermediate hosts.

Question 4

Transmission of endoparasites

Answer 4

Endoparasites of the body tissues are often transmitted by vectors.

Question 5

Factors increasing transmission rates

Answer 5

• The overcrowding of hosts when they are at high density.
• Mechanisms, such as vectors and waterborne dispersal stages, that allow the parasite to spread even if infected hosts are incapacitated.

Question 6

How do parasites affect the hosts behaviour?

Answer 6

Host behavior is often exploited and modified by parasites to maximise transmission. For example, alteration of host foraging, movement, sexual behaviour, habitat choice, or anti-predator behaviour.

The host behaviour becomes part of the extended phenotype of the parasite.

Question 7

Factors that increase virulence?

Answer 7

Parasites often suppress the host immune system, so that it can reproduce and surive without being attackted by hosts defences.

Modify host size so it grows larger and can support the asexual reproduction of more parasites.

Reduce the hosts reproductive rate in ways that benefit the parasite growth, reproduction or transmission by less energy spent on the hosts reproduction.