Week 5: Questions

Question 1

What does it mean to say that a pathogen is resistant to drugs?

Answer 1

That the drug is no longer able to kill or disable it because the pathogen has built a resistance to it.

Question 2

What does it mean to say that a human is resistant to a pathogen?

Answer 2

That our bodies have evolved and learned to fight off the pathogen

Question 3

Name and briefly describe one of the organisms living in or on your body that fits into each of the categories:

Answer 3

Commensalism- eyebrow mites (they eat dead skin cells and excess oil from hair follicles, but do not help or harm them in any way)

Mutualism- species in our digestive tract (help us to digest food, but also eat our food, so we are both benefiting)

Pathogenic- malaria (they infect red blood cells, reproduce inside them and burst the cells to release new parasites, so they benefit but cause harm to us)

Question 4

Can an organism change from one category of species interaction to another? Explain your answer

Answer 4

Yes because an organism may start off as being helpful (commensalism/mutualism), but if something transpires such as a population explosion it can become harmful (pathogenic)

Question 5

Why do bacteria and fungi produce antibiotics?

Answer 5

So that they can fight off and become resistant to the bacteria that they are in competition with

Question 6

Explain how the two conditions that are necessary and sufficient for natural selection to produce evolution of antibiotic resistance are met in a bacterial population

Answer 6

Condition #1: there must be variation in a population with respect to a specific trait, and this variation must have a genetic basis- some bacteria have antibiotic resistance while others do not, those with it can pass it on when they reproduce

Condition #2: variant individuals must differ in the number of healthy, reproductive offspring that they produce- those with the resistance will be able to survive longer because they can fight against antibiotics meant to kill them, therefore they can reproduce more

Question 7

What variation in antibiotic resistance is present in the bacterial population?

Answer 7

When bacteria is exposed to antibiotics, some will die, but there will be some that survive and become resistant to it

Question 8

Does this variation in antibiotic resistance have a genetic (heritable) basis? (Describe the effects of genes that produce antibiotic resistance in bacteria.)

Answer 8

Mutations cause some bacteria to have the resistance gene, which is passed on as they reproduce
Effects include being generally outcompeted by other non-resistant cells if antibiotics are absent

Question 9

Do bacteria with and without antibiotic resistance have a fitness advantage in an environment without antibiotics? In an environment with antibiotics? Explain your answers.

Answer 9

Bacteria with resistance

In an environment with antibiotics: yes because since they have a resistance, they will be able to fight it off
In an environment without antibiotics: no because it will actually use more of their energy when it isn’t required

Bacteria without resistance

In an environment with antibiotics: no because they will not be able to fight it off, so they will die
In an environment without antibiotics: yes because they will not be using extra energy where it isn’t required

Question 10

Some fruit flies evolved resistance to DDT in order to survive.

Answer 10

True

Question 11

Individual fruit flies became more resistant to DDT over time

Answer 11

False, since this is a process that occurs as a result of natural selection: Populations of fruit flies became more resistant to DDT over time

Question 12

When DDT was widely used, fruit flies with DDT resistance had greater evolutionary fitness than fruit flies lacking DDT resistance.

Answer 12

True

Question 13

Alleles for DDT resistance arose by mutation during the period of DDT use because of selection for pesticide resistance.

Answer 13

True

Question 14

Explain why highly virulent cholera bacteria were at a selective advantage during this outbreak

Answer 14

Because they did not have an antibiotic to fight against, so it was able to just keep spreading and make individuals more sick

Question 15

Over the course of the outbreak, would you expect that the disease became more virulent, less virulent, or stayed at the same level of virulence? Explain your reasoning

Answer 15

More virulent because its transmission is increasing

Question 16

The cholera outbreak spread into neighbouring countries like South Africa, where water purification was available. Do you expect that the disease became more virulent, less virulent, or stayed at the same level of virulence in neighbouring countries with water purification? Explain.

Answer 16

It became less virulent because there was reduced transmission

Question 17

In past years, Simon Fraser University has been very active in raising money for insecticide treated mosquito bed-nets. Using the principles of evolutionary medicine, explain why use of these bed-nets not only reduces transmission of malaria, but also selects for lower virulence of the malaria parasite.

Answer 17

They reduce transmission because it prevents mosquitos from being able to infect people with malaria
This selects for lower virulence because malaria is unable to transmit as much, therefore its virulence will decrease

Question 18

The video describes an American tourist who contracted Marburg virus, a hemorrhagic fever, when visiting bats in a Uganda cave. Search for information about Marburg disease or Marburg hemorrhagic fever on the Internet and determine which of the stages in Figure 10.17 the disease has reached.

Answer 18

Stage 4: epidemic

Question 19

Your textbook states that changes in behavior and ecology may help pathogens move through the stages in Figure 10.17 to infect, be transmitted by, and cause epidemics in a new species. What features of the behavior and ecology of humans and other primates led to the transmission of HIV/AIDS from chimps and sooty manganey monkeys to humans and may lead to the transmission of diseases from humans in Bwindi Impenetrable Forest to mountain gorillas?

Answer 19

People in Africa were initially exposed to HIV through the hunting of chimps

When they are the chimps, their blood entered the human bloodstream, infecting it

Larger human settlements allowed the virus to spread more easily

When there were attempts of controlling the disease, syringes were reused, which helped to further spread it

Question 20

Why did the Vancouver Rat Project focus on the Downtown Eastside neighborhood?

Answer 20

Because factors associated with poverty promote rat infestation and rat human contact

Question 21

What human diseases were found in the rats captured in this project? What are the symptoms of these diseases? Is there evidence that people living in the Downtown Eastside have contracted disease by contact with neighborhood rats?

Answer 21

Leptospiral (can cause kidney or liver failure), MRSA (infected skin area)

There is not evidence of human contact

Question 22

What problems may arise from trapping or poisoning rats in the Downtown Eastside?

Answer 22

It can contaminate water

Question 23

What actions should Health Canada take to reduce the spread of antibiotic resistance?

Answer 23

Reduce use of antibiotics

This will make it so that the bacteria become less resistant and the antibiotics work more efficiently

Vaccinations

Administer vaccines so that when our immune system does come into contact with certain pathogens, it will already have been exposed to it and able to fight it off better
These vaccines could also target behaviours rather than the organism itself (this way, the cells will continue to live, but not produce toxins because they won’t be in competition)

Reducing a disease’s transmission rate

This will select for milder strains of the disease because diseases that require personal contact are less lethal than those who do

Question 24

Should the government simply make recommendations for prescription and use of antibiotics, or should they bring in legislation enforcing best practices for antibiotic use?

Answer 24

Bring in legislation so that antibiotic use is reduced and only used when its really necessary

Question 25

With reference to the two conditions that are necessary and sufficient for natural selection to produce evolutionary change, explain how the diphtheria vaccine has brought about lower virulence in populations of diphtheria bacteria.

Answer 25

Condition #1: there must be variation in a population with respect to a specific trait, and this variation must have a genetic basis- there will not be variance in the population that some cells are antibiotic resistant, so they will not need to make the toxin necessary to fight off competition (which makes us sick)

Condition #2: variant individuals must differ in the number of healthy, reproductive offspring that they produce- cells will not reproduce and pass on the antibiotic resistance gene because they do not have it

Question 26

On page 307, your textbook describes how behavioral and social practices may select for more or less virulent strains of HIV. Insite, the only legal supervised drug injection site in North America, has been operating on East Hastings Street in Vancouver in 2003. It provides fresh needles and supervision for addicts injecting drugs. Would use of fresh needles by injection drug users tend to select for a more or less virulent strain of HIV?

Answer 26

Because this will result in less transmission, which means the strain will not become more virulent