#25 - Must Be True

[Administrator]

Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=11562)

The correct answer choice is (B)

The justification for the correct answer can be found on:

(lines 22-30; 49-59)

In the passage discussion of rhinoviruses, which cause the common cold, they are presented as examples of less virulent, directly transmitted pathogens whose lifespan is measured in hours. Correct answer choice (B) explains why such viruses are less virulent; they can be transmitted directly but cannot last long outside their hosts. The other answers are incorrect, because the rhinovirus’ limited virulence is not attributable to premature host immobilization, as suggested by answer choice (A), rhinoviruses are transmitted directly, not by vectors, as suggested by answer choices (C) and (D), and answer choice (E) would not explain limited virulence.

[jrc3813]

I had trouble choosing between B and C. Initially I chose B because the last paragraph mentions how some "wait and see" pathogens can be the most lethal, unlike rhinoviruses which die quickly outside the host. That supports B really strongly but I wanted to better understand why C is wrong. I understand that rhinoviruses are not transmitted by vector but are instead transmitted directly, but I didn't think C necessarily implied that rhinoviruses are transmitted by vector. Paragraph 3 explains why vector based pathogens are more deadly and that's because they are able to be passed on despite immobilizing the host, and because they can reproduce to such a concentration that a mosquito can obtain a high dose. I kind of thought about it in conditional terms I suppose:

High virulence High concentration/Dose Vector based Not Transmitted directly.

So if you are transmitted directly, you don't produce in sufficient numbers to pass on high dosages to a vector and are therefore not as lethal.

Basically if a pathogen is vector based, it has mechanisms that allow it to be more deadly. If you are a direct transmitter pathogen you aren't afforded those same mechanisms and are thus not as deadly. That's what I interpreted C to mean. Does that make any sense?

[Adam Tyson]

It does indeed make sense, JRC, but there is one aspect of your analysis and of answer C that should kill it for you, and that is the key difference between "survive long enough" and "reproduce in sufficient numbers". Vector-borne pathogens have no relationship to long-survival rates of the pathogens (at least, none that is described for us in the passage). Rather, they are related to the high concentration of the pathogens in the incapacitated hosts. Long survival times do not appear to be required for vector-borne pathogens - they just need to reproduce in large enough numbers so that a vector can pick up enough of them at one time to transfer a sufficient dose to infect a new host. Where long survival times matter is with the "wait and see" pathogens, which are not vector-borne. Tricky, right?

You're doing good work! Keep pounding!

[lsatstudying11]

Hello!

I can see why B is the correct answer, but I am struggling with understanding the problem with C. Since the third paragraph explains that the high virulence of some pathogens is a result of the fact that they reproduce in numbers large enough to allow vectors to get a high dose of the pathogen and then pass it on, wouldn't C make sense? It feels to me like C indicates that rhinoviruses are not likely to be especially virulent because they do not fit the pattern of vector-borne pathogens defined in paragraph 3. Where am I going wrong here? Thank you!

[Adam Tyson]

I see two problems with that answer, studying. First, the passage never implies that rhinoviruses are less virulent because they cannot reproduce enough to be carried by vectors. That causal argument is backwards, if anything - they don't reproduce enough to be carried by vectors because they are not virulent enough! The second problem is that the discussion of vectors in the third paragraph is not about rhinoviruses, but about pathogens that ARE carried by vectors, implying that rhinoviruses simply aren't that kind of pathogen. Rhinoviruses and vectors are not connected in any way, so the passage is not implying anything about a relationship between them other than that there is no relationship.

So, while C may be true (or may not), it is not implied by the passage, and since the question is asking for an implication we can draw from the text, we have to reject it.