topic 10 Host-parasite & host-disease interactions

Question 1

four kinds of attackers

Answer 1

• Predators
  
  • Parasites
  • Parasitoids
  • Herbivores

Question 2

*

* Parasitoid lifestyle

Answer 2

An animal that develops and grows on or inside a living host and kills the host when it emerges as an adult

Question 3

• Parasitoid population dynamics

Answer 3

• Parasitoid-host dynamics similar to predator-prey dynamics
  
  • • Often oscillatory, with parasitoid lagging behind prey
  • • Stabilized by similar mechanisms

Question 4

Parasite:

Answer 4

• Parasite: an organism that lives on or in (& feeds on) another living organism (its host), without necessarily killing it
•
• May or may not cause disease
• Most organisms have a suite of parasites
Not necessarily severely negatively affected

Question 5

disease, pathogen, effect?

Answer 5

• disease: an atypical condition in living organisms that causes some sort of physiological
impairment.
Pathogen: anything that can produce disease
Effect may be:
• Lethal (direct effect on d)
• Sub-lethal
– Reduced b
– Indirect effect on d (captured easily by predators, compromised immune system)
• Microparasites usually more pathogenic e.g., virus
(HIV), bacteria (salmonella)
• Macroparasites usually less pathogenic
– e.g., tapeworms, ticks

Question 6

horizontal vs vertical transmission? Transmission of parasites

Answer 6

• Horizontal vs. Vertical
• Horizontal transmission: the transfer of disease among
different individuals of the same generation.
• Vertical transmission: the transfer of disease from
parent to offspring.
Ectoparasites (e.g., leeches, bot flies)
• Repeated transmission between hosts
• Usually capable of independent movement outside host
(active transmission)
○ Ex leech swims to host = active transmission
• Endoparasites (e.g., tapeworm, hookworm, Giardia)
• Usually transmitted once/parasite generation (or less)
• Often not capable of independent movement outside host
(must rely on other routes of transmission

Question 7

Transmission of parasite ways

Answer 7

• Direct: parasites passed by contact of an infected individual with an uninfected
individual (mononucleosis virus)
• Environmental: parasites transmitted through air or water
– Giardia or Beaver Fever (protozoan)
• Vectored: transmitted by another unaffected species
– West Nile vectored by unaffected mosquitos
– Population dynamics of vectored parasites depend on
hosts & vector populations
• Indirect: transmitted via an intermediate host (who is also attacked)
– Common among parasitic worms: tapeworms, nematodes

Question 8

SIR model assumes

Answer 8

• IMPORTANT MODEL ASSUMPTIONS:
○ All individuals within each sub population are equal
○ Does not consider disease abundance within a host (infected or not)
○ Does not consider variation in individual susceptibility (nutrition, genetics)

Question 9

• Population dynamics of disease

4 interesting phenomena

Answer 9

○ Critical host population size (critical threshhold)
○ Immunity and disease cycles
○ Herd immunity
○ Disease eradication

Question 10

• Critical host pop. Size

Answer 10

Direct transmission ineffective in small populations

• Many diseases have a critical host population size required for persistence

Question 11

• Disease cycles and immunity

Answer 11

Diseases tend to cycle in prevalence (epidemics/epizootics)
Immunity: resistance to infection often acquired by a host
after experience with infection
ex rabies

Vaccination programs suppress cycles

Question 12

• Herd immunity

Answer 12

• Resistance of a population to the spread of a disease due to high rates of
immunity among individuals within the population.

Question 13

• Disease eradication

Answer 13

Worldwide vaccination programs can permanently eradicate diseases
• Smallpox eradicated in 1977
• Rinderpest (viral disease of ungulates)
eradicated in 2001
• Polio nearly eradicated in 2013
(~300 cases in Pakistan, Afghanistan & Nigeria)