though introduces a contrast which is not required here

while introduses a case happening at the same time when the other is occuring...

and IMO the s/c here is describing that the disease is afflicting some people while sparing others is more appropriate then saying that

the disease afflicts some people , though it spares other

E for me
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This is a tricky question in so far as whether it tests pronoun ambiguity or //ism. However, together with these two factors, in my personal opinion, there is a third but IMO primary factor, namely the use of appropriates a subordinate conjunction. The text intends to say that it afflicts some people at the same time it spares some others. This simultaneity is the essence of this topic, I feel.


(A) though it spares… The pronoun’s ambiguity, though not very critical, is in play and the conjunction – though - shows contrast but not concurrentness

(B) where it spares… The pronoun’s ambiguity, though not very critical is in play and the conjunction – where - shows a place of action rather than concurrentness

(C) despite sparing ------ Despite does not bring out simultaneity

(D) when sparing ------ When does not bring out contrast
(E) while sparing -------- while brings out contrast as well as simultaneity; hence, the preferred choice.

However, do GMAT questions skate on such thin ice? Very odd.
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Answer E.
I can tell why when and where are wrong
and why is option A here is wrong due to the usage of "it"
Despite --- in spite of
I dont know why despite is wrong but I preferred While over despite.
usage of While
It can actually mean two things:
1) while = at the same time as.
2) while = although, or some sort of contrast.
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OA is E. The point is that we need a description that can either contrast the two situations (different groups of people), or demonstrate their happening simultaneously.

(A) though it spares
Wrong for two reasons.
(1) In GMAT, we can say for sure that it is incorrect to use one SAME PRONOUN more than twice.
(2) You often use "though" to introduce a fact that you regard as less important than the fact in the main clause.

(B) where it spares
Wrong for "it". In GMAT, we can say for sure that it is incorrect to use one SAME PRONOUN more than twice.
Note: "where" is correctly used here.
You use "where" to introduce a clause that contrasts with the other part of the sentence.regard as less important than the fact in the main clause.

(C) despite sparing
Wrong for "despite"
You use "despite" to introduce a fact that makes the other part of the sentence surprising.

(D) when sparing
Wrong for "When"
You use "when" to introduce a fact that makes the other part of the sentence surprising or impossible.

(E) while sparing
Correct.
You use "while"
(1) before making a statement, to introduce a fact that partly conflicts the following statement.
(2) to introduce a fact that happens simultaneously with the following statement.

In A and B, it is not that the pronoun ‘it’ has no proper referents. The problem is that ‘it’ refers to two different things. The first ‘it’ refers to the bacterium and the second ‘it’ refers to the disease. Ambiguity is not an issue but the multiple references are.

Despite is inappropriate in this context because despite always involves a paradox. Say like: Despite my low GMAT score, I got admitted into the Ivy League; Churchill was sure of his victory despite the series of defeats until the very end. etc, etc.

So E wins
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