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Lyme disease is caused by a bacterium transmitted to humans

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Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following, if true, strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes lyme disease in humans.

B. There are no known cases of a human's contracting lyme disease through contact with white-footed mice

C. A deer tick feeds only once while in the larval stage

D. a single host animal can be the source of bacteria for many tick larvae.

E. none of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans.

[Reveal] Spoiler:
i found the same stem but different question. can anyone explain this?
[Reveal] Spoiler: OA

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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Responding to a PM.

Question 54: (S) Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument?
A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans

I think, given the terminology and sentence structures used, this passage is not very easy to understand. Let's first understand the passage:

Understanding the passage:

1. Disease: Lyme
Caused by: bacteria
Source of bacteria: Deer ticks
2. Deer ticks pick the bacterium in their larva stage, from infected white footed mice
3. White footed mice is not the only food of Deer ticks - there is some food which does not contain this bacteria
4. Conclusion: If this 'other' food, which does not bacteria, is increased:
a. the number of deer ticks, who get bacteria, will reduce
b. the number of humans, who get infected by Lyme disease, will reduce

Prethinking:

If we read 3 & 4 together, we can see that the link between the premise and the conclusion is that once these deer ticks will have 'other' food to feed on, they'll stop or reduce eating white footed mice.

One more thing to observe, before we move on to the option analysis, is that there are two parts of the conclusion; therefore, a strengthener can strengthen either of these two parts.

Analysis of Answer Choices:

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans - Whether Ticks suffer or not is not our concern here. This is Out of Scope.

B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice - This means that humans acquire this from Deer Ticks only - same as first statement of the passage. No new information provided. Thus, this cannot be the correct choice. Incorrect.

C. A deer tick feeds only once while in the larval stage. - If a deer tick feeds only once in the larval stage, then once it has eaten something which is not infected, it'll not acquire the bacterium through this way. Therefore, if we increase the amount of uninfected feed, the probability that a larvae will eat uninfected feed will increase and therefore, its probablity of acquiring the bacterium will decrease. This, therefore, seems to strengthen the argument. For surity, let's also look at the remaining two choices.

D. A single host animal can be the source of bacteria for many tick larvae. - Whether a single host affects only one tick larvae or multiple larvae, it doesn't impact the conclusion at hand. Increasing the amount of uninfected feed should still decrease the probability of deer tick feeding on these infected mice.

E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans - The issue is about Lyme disease only. Therefore, this is out of scope.

On the basis of our analysis, we can see that option C clearly emerges as the correct answer choice.

Hope this helps :)

Thanks,
Chiranjeev
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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This is a very interesting and somewhat tricky question. Here is my analysis of this question.

Bacteria -> whitefooted mice -> larvae of deer ticks -> humans
Larvae also feed on 'other species' which do not harbor the bacterium.

Conclusion: Increase the population of 'other species'; fewer people will get Lyme disease.

Strengthen the conclusion:

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.

Out of scope.

B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.

Out of scope. Argument doesn't discuss whether humans can directly contract Lyme disease. The argument only deals with Lyme disease through deer ticks. Let me elaborate on this. Say 100 people contract Lyme disease every year. At least some of them are through infected deer ticks. If number of infected deer ticks is reduced, the number of infected humans will reduce too. It is immaterial whether there are other ways of contracting lyme disease. If all 100 humans get infected through deer ticks, the number of infected humans might go down to 50. If half get infected directly and half through deer ticks, number of infected humans may go down to 75. In any case, we do expect the number of humans infected to go down. Hence, we can say that option (B) has no relevance as far as our conclusion goes. We are only concluding that there will be a decrease - not the amount of decrease.

C. A deer tick feeds only once while in the larval stage.
If there are more uninfected food sources, it is likely that when the larvae feed, they feed on uninfected food. If the larvae do not feed again, it is probable that they will not carry the bacterium of Lyme disease and hence fewer humans will get affected. Answer (C)

D. A single host animal can be the source of bacteria for many tick larvae.
It doesn't strengthen our plan since bacteria could still proliferate if a single host can be source for many tick larvae. So we may not see much decrease in Lyme disease in humans.

E. None of the other species on which deer tick larvae feed harbor other bacteria that
ticks transmit to humans.

Out of scope.
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Here is the conclusion of the argument.

If the population of these species(species which even after eating infected white-footed mice do NOT pickup bacterium) increased, more of the larvae(deer ticks species) would be feeding on uninfected hosts, so(Conclusion indicator) the number of ticks acquiring the bacterium would likely decline.

In other words, we can say that the argument is concluding by stating that if the population of the species which do not pickup bacterium even after eating infected white-footed mice is increased, then most of the infected white-footed mice will be eaten by these species. And the rest of the food is somewhat better for the deer ticks species and this can reduce to some extent the number of deer ticks acquiring bacterium which inturn reduces the number of humans getting Lyme disease.

Now look at the answer choices – which support this conclusion - reason for deer ticks acquiring bacterium reduction / humans getting the Lyme disease reduction

1. Consequences from carrying bacterium have no impact on the number of humans getting Lyme disease. Rule out this option.
2. Cases of Human’s contracting Lyme disease thru contract is white-footed mice have no impact on reducing the number humans getting Lyme disease. Rule out this option.
3. This looks supporting the conclusion because – deer ticks(a species) feeds only once while at larval stage and at this stage if the feed available is NOT contaminated, then they do not pick up the bacterium and there by reduce the number of humans getting Lyme disease. Possible ans.
4. One host animal being the source for many deer tick larvae to pick up the bacterium --> indicates even with one infected animal many deer ticks can pick up bacterium --> leading to more humans getting Lyme disease. Weakening the conclusion. Rule out this option.
5. Deer ticks getting other bacterium is irrelevant because the argument is taking abt the bacterium leading to Lyme disease. Rule out this option.

My pick is C.

here is a link detailing the explanation on how to solve this question type. (Note that there is slight change in the wordings of the conclusion.)

http://www.manhattangmat.com/forums/post2001.html
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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raviram80 wrote:
Hi All

Could some one help with the cr question below. This is from the GMAT Prep CR.pdf document

Question 54: (S) Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument?
A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that

I could not understand the answer choice


First, you should comprehend the contend of the argument.

Dear ticks contain bacteria (Lyme disease) only in white footed mice, the other species that the dear ticks feed on them do not contain bacteria => Notice: All of the dear ticks are on larvae stage

Conclusion:
IF Other species increase, THEN ticks (have bacteria) & people (get the Lyme disease) will decline

The question is strengthen type. You can also use Negate technique. Negating choice C, If the deer ticks can feed on another stage beside larva stage => Ticks possibly develop on others animals and contain diseases. So, will weaken

=> Choice C is the correct one

Hope that helps
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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X disease -> to humans -> from deer ticks.
larva deer ticks -> from feeding white footed mice (culprit)
Other food sources of "deer ticks" do not cause infection.
So if other food sources are increased, "deer ticks" would feed on them and refrain from feeding white footed mice.


What if, deer tick larva feeds both on white footed mice and alternative source ? My conclusion won't be valid in that case.

Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.
I am not bothered about suffering if ticks
B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.
Does not help. Number of white-footed mice remain same before/after increased other food sources for larvae. Humans would be benefited by decreased infected ticks.
C. A deer tick feeds only once while in the larval stage.
If deer ticks feed only once in larval stage and they have abundant infect free sources, then there will be less infected ticks and our conclusion that humans will be safer holds valid.

D. A single host animal can be the source of bacteria for many tick larvae.
That is possible, but we are not concerned on number of mice. If alternative food sources are availble, atleast some ticks would be non-infected.
E. None of the other species on which deer tick larvae feed harbor other bacteria
already clarified in the premise, " certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species "
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following, if true, strengthens the argument?

a. Ticks do not suffer any adverse consequences from carrying the bacterium that causes lyme disease in humans.
This is irrelevant


b. There are no known cases of a human's contracting lyme disease through contact with white-footed mice
Again Irrelevant

c. A deer tick feeds only once while in the larval stage
If they feed once, then by the concept of mathematical probability, the less the proportion of the infected host the less the chances of the spread of the bacterium

d. a single host animal can be the source of bacteria for many tick larvae.
Actually weakens the argument

e. none of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans.
Irrelevant

Hope this helps...
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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Choice E talks about other bacteria that also cause Lyme disease, but the argument talks about Lyme disease that is caused by only bacteria transmitted to human according to the argument. The other bacteria, we do not know how it can make human be disease. So, it is out of scope.

P/S: you should edit your choice E in the initial post to help other members see the full meaning. Thanks
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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scp wrote:
Chranjeev and E-gmat

This definitely helped.

there is another version of this question
Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

Which of the following would it be most important to ascertain in evaluating the argument?

(A) Whether populations of the other species on which deer tick larvae feed are found only in the areas also inhabited by white-footed mice.
(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
(C) Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice.
(D) Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed.
(E) Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans.

Can we say that evaluate and strengthen is the same?
Also see my analysis on this one ( based on the the prethinking you did :)

A) Not relevant because even if other species is found in the area inhabited by white footed mice, it does not mean that other species will pick bacterium
B)Can be relevant - if the animals to feed on are not limited we cannot say that deer ticks larvae will move to other species. Lets park it
C) OFS, the conclusion is different than this solution
D)On first glance this looks relevant but than a careful read of the passage tells us that " deer ticks pick up the bacterium while in the larval stage" so they cannot pick up the infection as adults. Though I get the logic but i am still tempted by this choice and might pick this on test day becaue it in a way is saying that the plan of reducing the infectiong by introducing other species might not work ???
E) Any other bacteria is OFS

let me know if my analysis is correct and how can I definitely eliminate D? Would applying variance test work?

Thanks a lot


Hi Scp,

You are correct that Choice D is indeed tempted. However, that is so till the time we don't understand the nuances of the passage and the conclusion. Let's understand this:

".... so the number of ticks acquiring the bacterium would likely decline" - If we eliminate one way of acquiring infection, wouldn't "incidence of infection" likely decline - even if there are other ways of acquiring infection (as suggested by option D. Option D, though tempting, doesn't really effect the conclusion.

Besides, if we read the passage, it says that "...Generally, deer ticks pick up the bacterium while in the larval stage..." - this means that getting infected at larvae stage is one of the most common ways to acquire infection. Thus, eliminating this should surely help.

Now, why option B is correct?

This is because it asks us to know the presence of any preference of deer ticks towards white footed mouse.

(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.

If the answer is yes, then it means that deer ticks probably eat white footed mice due to lack of other food and if that other food is increased, they will probably stop eating these infected mice. Therefore, the conclusion will hold.

If the answer is No, then it means that deer ticks eat these white footed mice in spite of other abundant food, so these deer ticks probably have some preference for these mice - therefore, increasing other food might not help. Therefore, the conclusion will not hold.

Hope this helps :)

-Chiranjeev
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Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally
deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that

Why option B is wrong


Hi,

I'll just focus on your question that why B is incorrect.

Let's first identify the conclusion:

Conclusion: if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

So, this is a causal argument i.e. an argument which says that if you do X, you'll achieve Y.

In this specific case, it says

IF population of these other species were increased (X), then,
1. the number of ticks acquiring the bacterium would likely decline(Y)
2. and hence the number of people contracting Lyme disease would likely decline (Z)

A strengthener is a statement which increases our belief in the conclusion. Let's look at option B to find out if it does so.

B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice.

It means that humans cannot directly acquire Lyme disease through white-footed mouse. But how does it affect the conclusion? If one of the ways of acquiring a disease is reduced, it should lead to a "decline" in the incidence of disease, irrespective of the fact that there are other ways to acquire a disease.

For example: If a disease X can be acquired through two mediums: A and B.

If I decrease A, then it should lead to a decline in X, irrespective of the fact that there are other ways to acquire the disease.

However, there is a catch. If the conclusion had stated that the disease will be eliminated, then in that case I would need to consider whether there are other ways to acquire the disease or not.

Hope this helps :)

Let me know if you have any further queries.

Thanks,
Chiranjeev
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monikaleoster wrote:
Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally
deer ticks pick up the bacterium while in the larval stage from feeding on infected white footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline.

Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that
causes Lyme disease in humans.
B. There are no known cases of a human’s contracting Lyme disease through contact
with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that

Why option B is wrong


Hi,

Here is the detailed analysis of this question.

Understanding the Passage

Premises:

1. Lyme disease is caused in humans by DT (Deer Ticks)
2. DT pick up the bacteria in the larva stage by feeding on infected WFM (White Footed Mice)
3. DT also eats other species which don't have bacteria

So, (conclusion) if we increase these OS (other species), the number of DT with bacteria will reduce and this will lead to reduction in the number of incidence of disease in humans.

Can you understand how the conclusion is drawn?

Let's understand it.

DT eats OS and WFM.

For illustration, let's suppose there are 50 OS and 50 WFM. In such a scenario, the probability of a DT eating WFM is 50%. Now, suppose we increase the number of OS to 450, then we have total of 500 eatables out of which only 10% are WFM, so now the probability of DT eating WFM has come down to 10%.

Therefore, if we increase OS without increasing WFM, the number of DT acquiring bacteria should reduce. This is the conclusion.

Prethinking

Here, let's think of an assumption built in the above conclusion.

It's a bit difficult if you are not very comfortable with random events and probabilities.

The assumption is that DT does not have a preference of eating WFM over OS because if DT does have a preference, then even if we increase OS, DT will still eat WFM as long as WFM exists. Thus, for our conclusion to hold, this assumption is required.

For people familiar with random events and probability, read this; other can skip directly to Analysis of Option statements

Look at the example we took above in which we said that increasing OS to 450 and keeping WFM at 50 will make the probability of eating WFM 10%. This is based on the assumption that eating by DT is a random event or in other words, DT eats randomly whatever is lying in front of it. If we keep more OS, then the probability of eating OS will increase. However, if eating by DT is not a random event and is rather skewed towards certain possibilities, then increasing OS might not help.


Analysis of option statements

Before marching on, remember that we are here to find a strengthener to the conclusion that increase OS will lead to lesser DT acquring bacteria and eventually lesser humans acquiring the disease

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. - Whether they suffer or not, it doesn't matter. They make us (humans) suffer. Not relevant. Incorrect.

B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. - This option indicates that humans don't acquire Lyme disease directly from WFM.

Let’s take the opposite and say that humans could contract Lyme disease from WFM. Now, when we increase OS, then DT will eat less of WFM. This will lead to an increase in WFM numbers. Since humans can acquire the disease directly through WFM, it would lead to increase in incidence of Lyme disease in humans. This creates doubt about the conclusion. So, this option, by indicating that humans don't acquire the disease through WFM, eliminates the doubt and hence, should be a strengthener.

But there is a catch – a flaw in the above reasoning. The truth is that DT don't kill WFM and then eat them. DT are very small insects - they can't really kill mice. Like a mosquito doesn't need to kill us to feed on us. So, even if DT feeds less on WFM, it won’t lead to an increase in the numbers of WFM.

Therefore, population of WFM doesn’t change on the implementation of the plan. Therefore, whether human can acquire Lyme disease directly through WFM doesn't affect the conclusion. Incorrect

C. A deer tick feeds only once while in the larval stage. – This requires some understanding.

Consider two scenarios:
1. Deer tick feeds only once
2. Deer tick feeds 20 times

First scenario: Deer tick feeds only once

Suppose we have 80 OS and 20 WFM. What is the probability of deer tick getting the bacteria?
Simple. Probability = 0.2 (i.e. same as proportion of WFM)

Second scenario: Deer ticks feeds 20 times.

What is the probability of deer tick getting the bacteria?
Remember that DT gets the bacteria even if it feeds on WFM for only once out of 20 times.
So, we can say that Probability = 1 – P (DT not feeding on WFM even once)
= 1 – (0.8)^20
= 1 – 0.11
= 0.89

So, what do we see?
If DT eats more number of times, then even with the same proportion of OS and WFM, more DT gets bacteria.
Therefore, when DT eats only once, reducing the number of WFM will have the most impact in terms of reducing the number of infected DT.

Therefore, this option strengthens the conclusion. Correct.

D. A single host animal can be the source of bacteria for many tick larvae. – This is fine but this will apply to both OS and WFM. If it applied to only OS, then it would strengthen our case like Option C. But since it applies to both, it doesn't impact the conclusion. Incorrect.

E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans – We are only concerned about bacteria related to Lyme disease. This doesn't affect the conclusion. Incorrect.

Hope this helps :)

Chiranjeev
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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New post 26 Oct 2009, 10:28
Very similar, but different post at tough-cr-lyme-disease-81209.html
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New post 01 May 2011, 10:45
Central argument: If populations of *other* species which deer ticks feed on in their larval stage increased, then fewer of the ticks would feed on white-footed mice, then the infection rate of the ticks would go down.

A - strengthens >> if the ticks don't suffer, then more of them survive to carry bacterium

B - irrelevant at best (the ticks are the issue, not the mice), weakens the argument at worst (if the mice have ticks, then argument would suggest contact with and infection of humans)

C - doesn't matter >> whether they feed once or 10x, they still will get the bacterium

D - strengthens >> if it's between one mouse and one "other species" then the effect one way or the other would be magnified

E - irrelevant >> "other bacteria" not in question


IMHO, D is a better answer than A. While A strengthens somewhat, D really makes the point that a single alternative host can mean the difference between lots of ticks getting the bacterium and lots not getting it. Add a few more species and the situation is magnified. Oppositely, take away alternatives to the mice and things get a whole lot worse.

If there's any hole in my reasoning, I welcome comments. As I can benefit from it too :-)
(Thanks in advance.)
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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New post 19 Aug 2011, 00:24
+1 C, reasons as stated above.

Please post the OA after sufficient discussion, this question is 2 years old and no OA/OE.
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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New post 20 Nov 2011, 10:26
OA is C
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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New post 20 Nov 2011, 19:37
i guess it is C
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Re: Lyme disease is caused by a bacterium transmitted to humans [#permalink]

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New post 04 Dec 2011, 05:22
+1 for C
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New post 27 Dec 2011, 22:38
Yes C it is. Thanks for the explanations guys.
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New post 28 Dec 2011, 17:54
+1 C
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New post 31 Dec 2011, 00:52
As bacteria in larvae stage feeds only once chances are it would feed on the non infected animals as they are more in number hence C.
Re: Lyme disease is caused by a bacterium transmitted to humans   [#permalink] 31 Dec 2011, 00:52

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