Lyme disease is caused by a bacterium transmitted to people by deer ti

The passage does tell us that the bacterium can be transmitted when deer ticks feed on an infected host, and that ticks can transmit the bacterium to people. At the same time, as you suggest, it never directly states that deer ticks can ONLY pass on the bacterium while feeding. Given all that, let's see if process of elimination helps with this one.

According to the passage, ticks in the adult stage CAN be infected with the bacterium. Since we know ticks can transmit the bacterium to people, there is no reason to think adult ticks can't infect people. Eliminate (A).

We know that the bacteria is transmitted when ticks feed (ticks "can pick it up from feeding on an infected host"). Does that mean ticks transmit the bacterium ONLY when they feed? We don't know that for sure, but that's not an unreasonable idea based on what the passage tells us. And if that's true, (B) would have to be true. Hold onto it for now.

The passage directly supports the idea that both nymph and adult stage ticks can be infected. Just as with (A), since we know that ticks CAN transmit the bacterium to humans, we have no reason to think nymphs or adults won't be able to infect people. Eliminate (C).

We know that ticks "can pick it up from feeding on an infected host in any of the tick's three successive stage of development: larva, nymph, adult." Since (D) is directly contradicted by the passage, we can eliminate it.

Just as with (A) and (C), we know that nymphs can be infected, and that ticks can infect people. By the same logic as (A) and (C), we have no reason to think that nymphs can't infect people. Eliminate (E).

That leaves us with (B), the correct answer.

While we don't have conclusive proof that the disease can ONLY be passed on when deer ticks feed, all the other answer choices have clear flaws. Additionally, since the passage tells us that the bacterium can be transmitted when deer ticks feed, (B) is logical and consistent with the passage. So while we can't prove it 100%, it is still the answer that "most logically completes the argument."

I hope that helps!

chetan2u

Could you explain why D incorrect? Is it an out of scope answer?

Thanks

Hi,

the reasoning is

the deer tick gets infected by feeding on a HOST carrying the disease. ALSO, the deer tick can feed on ONLY three persons in its entire life- ONE each in larva, nymph, adult.
1) The deer tick may not get infected at all if all these THREE host are disease -free...
2) OR it can get infected in any one of these stages and transmit the disease to its host in next stage...

what does D tell us--

D. People infected with the Lyme disease bacterium cannot transmit bacterium to adult deer ticks..

If an adult deer tick has not got infected in larva and nymph stages, and then it feeds on an infected person, the adult deer tick can get infected BUT it cannot transmit it to ANYONE else as it does not feed on any other person after feeding on ONE person in that stage..

so D is not OUT of context But it does not follow the logical reasoning of the PARA..

Thanks for this explanation. I was (and frankly still am) still thrown off by the 1st sentence of the stimulus, which says that deer ticks transmit Lyme disease, not that people transmit Lyme disease back to ticks. It seems like to even begin to arrive at the OA, you need to consider to be true that there can be human > tick transmission. This feels quite bizarre.

I was also split between A and B, but I picked A because the stem explicitly states "Once infected, a tick remains infected through any subsequent developmental stages" which means adult stage, too, hence A. Could someone explain why this is omitted from the analysis? Thanks!

The word "only" is the issue in option A. It is not correct that humans get infected ONLY by larval stage or nymph stage ticks - humans may ALSO get infected by adult stage ticks. (In that case, the adult tick must have taken up the basteria in larval stage or nymph stage.) Hence A is wrong.

Thank you! This makes sense but B is still contradictory because people CAN (not cannot) be infected by a tick that picked up the Lyme disease bacterium in the adult stage

No, people CANNOT be infected by a tick that picked up the Lyme disease bacterium in the adult stage . The reason is as follows:

The tick can feed "on ONLY ONE host in each stage". Suppose a tick comes to adult stage without any infection. Now in the adult stage it feeds on a host who is infected and picks up the disease. Now in adult stage this tick will NOT be able to infect anybody since it will NOT feed on any other host in the adult stage ( feeds on only one host in each stage). The tick can only infect a person in the SUBSEQUENT stage after picking up the disease. Since the tick dies after completion of the adult stage, it can't infect anybody after adult stage.

A deer tick can get infected by feeding on an infected host. But a tick can feed on only one host in each stage.

Possibilities:
1) Larva: Feeds and gets infected; Nymph: can transmit the bacteria; Adult: can transmit the bacteria
2) Larva: uninfected; Nymph: Feeds and gets infected; Adult: can transmit the bacteria
3) Larva: uninfected; Nymph: uninfected; Adult: Feeds and gets infected --> Cannot transmit the bacteria

Answer: B

A. Incorrect. 'only' makes the reasoning too strong as people can be infected even by adult stage deer tick
C. Incorrect. It is possible in both the scenarios
D. Incorrect. It may be possible.
E. Incorrect. Need not be true.

can someone explain the argument in a simplified way please??

can humans be the host?? so the deer feeds on human??? it doesn't make sense at all

how can the disease be transmitted? is it by feeding?? if it's by feeding then ok B) makes sense

OK .. trying to explain as simply as I can:

Deer ticks: an insect that has three phases (say I, II and III) in life. This insect is carrier of a bacteria (say X) that causes Lyme disease. The insect gets the bacteria X from someone else (say H1) while feeding on H1, who is already infected with the bacteria. Later the insect delivers the bacteria X to someone else (say H2) while feeding on H2.

The condition is that taking up and delivering of bacteria X cannot happen in the same phase of the insect's life because the insect feeds on only one animal or person in one phase of it's life (it cannot feed on both H1 and H2 in the same phase). If the insect gets the bacteria in phase I, it can deliver it in phase II or III. If the insect gets the bacteria in phase II, it can deliver it in phase III. If it gets in phase III, it cannot deliver at all.

Hosts: Hosts are the entities (could be humans or any animal) on whom the above insect feeds. H1 and H2 are both hosts (hosts of the insect).

Now read the explanations in the previous posts and hopefully you will understand the argument.

This is an INFERENCE question.
So, based on the given information, what can we conclude with certainty?

Let's start by summarizing the premises.
PREMISE: Deer ticks give people Lyme disease via bacterium.
PREMISE: Deer ticks seldom born infected with bacterium
PREMISE: Deer ticks get bacterium by feeding on infected hosts during 1 of 3 stages (larva, nymph, adult)
PREMISE: Tick remains infected through any further stages
PREMISE: Tick feeds on only one host in each stage

Next, we should try to come up with our own conclusion that follows from the premises.
NOTE: Don't spend too long doing so.
I can't think of a conclusion that follows from the premises, so let's head to the answer choices.

KEY: As we examine each answer choice, we should ask "Based on the given premises, MUST this conclusion be true?"

A. People can be infected only by being bitten by a tick that is either in larval stage or in the nymph stage
MUST this be true?
No. if a tick become infected during its nymph stage, it can later transmit the bacterium during its adult stage.
ELIMINATE A

B. People cannot be infected by a tick that picked up the Lyme disease bacterium in the adult stage
MUST this be true?
YES!!!
We're told that ticks feed on only one host in each stage. So, if a tick picks up the Lyme disease bacterium during the adult stage (the LAST stage of its development), then that tick got the bacterium from its ONE AND ONLY host during that adult stage.
Since the tick will not have any other hosts during that adult stage, and since the adult stage is the tick's LAST stage, there is no way that it can transmit the bacterium to a human
KEEP B.

C. It is not possible for a person to be infected by a tick that is in the nymph stage or by a tick that was infected with the bacterium while in the nymph stage
MUST this be true?
No!
We're told that deer ticks are seldom born infected with bacterium. So, it's POSSIBLE that a deer tick is born infected with bacterium, which means it can pass on the bacterium to a human host during it's nymph stage.
ELIMINATE C

D. People infected with the Lyme disease bacterium cannot transmit bacterium to adult deer ticks
MUST this be true?
No.
Deer ticks get bacterium by feeding on infected hosts. So, if a deer tick has a human host that is infected with Lyme disease bacterium, then a tick could become infected by the person.
ELIMINATE D

E. Only deer ticks that are adults can transmit the Lyme disease bacterium to people
MUST this be true?
No!
See rationale for eliminating C
ELIMINATE E

Answer: B

Cheers,
Brent

Dear GMATPrepNow Brent

I have a question about 'host'. Can the 'host' be a person? or others such animal, plants..etc? If it can't be a person, can tick pick up Lyme from an infected animal and transfer it to a person?

I'm confused.

Hi Mo2men,

I imagine that the host can be any animal (including people).
Yes, the deer tick can pick up Lyme from an infected animal and then transfer it to a person.
Which part of the question confuses you?

Cheers,
Brent

Hi Brent,

If people are not considered as 'host', then simply choice B is invalid. The tick can pick up Lyme from an anime (excluding human beings) during its adult stage and then bite a human being. But according to you, a human being is host too. So B makes sense.

The problem in that question is that I did not know what tick is but I took word 'deer tick' as if there a deer and its type called 'tick'. I did not understand until I googled it and understand what tick looks like. Then comes word 'host' and its definition. So the confusions stem from many places.

Thanks from help out as always

You're right, much of the question centers on the definition of "host"

Cheers,
Brent

I think the most important word in the question stem is "One Host" this tells us that deer ticks do not change the host (if deer tick feeds on a person A, it wont feed on person B) hence if the deer tick acquires an infection in adult stage (from Person A) it wont Transmit it back to person A (he/she is already infected!!). So B makes sense!