11. Evolution and origin of symbionts & spread of new epidemics

Question 1

What are symbionts?

Answer 1

• organisms living together

Question 2

Commensal

Answer 2

symbionts that benefits and does not harm the other

Question 3

Parasite

Answer 3

Symbiont that benefits and harms the other partner

Question 4

Mutualists

Answer 4

Symbionts that both benefit each other

Question 5

What is demodex?

Answer 5

• a harmless commensal

* type of mite

Question 6

Sarcoptes

Answer 6

• an ectoparasite that burrows under the skin and causes scabies

Question 7

Describe host-parasite evolution

Answer 7

• parasite evolves to be less harmful

* hosts evolve to be resistant - resistance hosts reproduce more

Question 8

Why do parasites evolve to be less harmful?

Answer 8

• a parasite is not transferred if the host is killed rapidly
• parasite benefits if the host is abundant

Question 9

What do commensals found commonly in our guts do?

Answer 9

Eat compounds that we cannot digest

Question 10

What do mutualists thats found commonly in our guts do?

Answer 10

• Partly digest food - we then absorb it
• some manufacture B&K group vitamins
• some produce useful compounds (stimulate immune system)
• some feed on harmful excretions of other bacteria

Question 11

What is the bifidus bacteria?

Answer 11

Bifidus bacteria is found on vagina, nipples of lactating women
• ensure the baby gets bifidus
• protects by decreasing other bacteria

This ensures the antibody system starts - it is important that pathogens are low/absent

Question 12

Explain why the tasting behaviour of babies is beneficial

Answer 12

• stimulates crossover immunities

* ensures child is exposed to all common bacteria

Question 13

Name of bacteria that causes the plague

Answer 13

Yersina pestis

Question 14

How is the bubonic plague transmitted?

Answer 14

• ball of bacteria - blockage in flea’s gut
• flea is hungry and looks for new host
• sucks harder, fails, recoil shoots bacteria into bite wound

• also humans can transmit it through coughing

Question 15

What are the risks factors that exotic zoonoses will enter Australia?

Answer 15

• animal hosts/ vectors are in Australia already
• host lives close to humans
• disease incubation period long (ie. long time before symptoms show and treatment can be sought)

Question 16

What factors affect the spread of disease amongst a population?

Answer 16

• density and movement of hosts
• size of host population
• nutritional & knowledge status of host population

Question 17

How does density and movement of hosts affect spread of disease?

Answer 17

• high density = greater contact between individuals

* more movement

Question 18

How fast do diseases spread?

Answer 18

Depends on transmission between hosts
•horizontal transmission - between individuals or via vector/intermediate host

•Vertical transmission - between generations, mother to child

Question 19

What assumptions do we have when tracking the number of infected?

Answer 19

• assumes the population is large

* very few immune

Question 20

What is the rate of spread of a disease?

Answer 20

• r= P x C x D
• P = probability of passing on disease (At each contact)
• effective average # of contacts / year
• D = duration of infectiousness

Question 21

How do we know if these is an epidemic using the formula?

Answer 21

• if r>1 there is an epidemic

* where r = P x C x D

Question 22

What role does ecosystem disturbances have on infectious disease?

Answer 22

• brings humans into contact with new hosts & parasites
• contact bw domestic and wild animals
• increases nutritional stress in wild populations
• greater chance of spreading any native pathogens

Question 23

How should we achieve bio-awareness?

Answer 23

• reduce bio-pollution
• immunisation
• public health measures
• better control of pests
• minimise evolution of resistance
• expand bio-control research
• anticipate climate change effects