AH Biology - Unit 2 - KA5(c) - Transmission and Virulence

What is transmission?

Transmission is the spread of a parasite to a host.

What is virulence?

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

What is an ectoparasite and how are they transmitted?

An ectoparasite is a parasite found on the surfaces of the host. For example, fleas or ticks. They are transmitted by:

• Direct contact

• Consumption of an intermediate hosts.

What is an endoparasite?

An endoparasite is a parasite found inside host tissues. For example, viruses. They are transmitted by vectors.

What are the two main factors that increase the transmission rate?

The two main factors that increase the transmission rate are:

• Overcrowding of hosts when their population density is high

• Mechanisms, such as vectors and water borne dispersal stages, that allow a parasite to spread, even if the infected host is incapacitated (can’t move).

What is often done to host behaviour by a parasite, and what does this become part of?

Host behaviour is often exploited and modified by a parasite to maximise its transmission. This modified behaviour becomes part of the extended phenotype of the parasite.

What modified host behaviours might extended phenotypes include?

Extended phenotypes may include modified host behaviours such as alterations to:

• Host foraging

• Host movement

• Host sexul behaviour

• Host habitat choice

• Host anti-predator behaviour

Aside from modifying the host’s behaviour what else can the parasite do?

Aside from modifying the host’s behaviour, the parasite can also:

• Suppress the host’s immune system

• Modify the host’s size

• Modify the host’s reproductive rate to benefit the parasite’s growth, reproduction, or transmission.