This is a set of facts that we need to consider in order to find the answer choice that is most strongly supported. Our task is simply to fact find. There is no need to predict an answer choice and there is no need to ponder before going to the answer choices.
Once you start considering each answer choice, ask yourself whether it is strongly supported by the passage or not. It will either be paraphrased directly from the passage or a the result of combining multiple facts together.
Let's now examine answer choice A.
It states that West Nile virus will never be a common disease among humans. But this is not supported in the passage at all. For all we know, it is very possible that humans inhabit an area where there are many infected mosquitos. There is nothing to suggest that it would not become common among humans in this case. Or perhaps, an animal with West Nile virus is brought to a West Nile virus-free area. This animal then affects the mosquitos that bite it, which in turn affects the human population.
Answer choice E is correct because a human doesn't transmit the virus to mosquitos when they are bitten. This means that it won't spread from this human to others through mosquitos. Note that this is a most strongly supported question, and not must be true. It is still possible that a human did bring this disease to North America if they donated blood or some other means of sharing blood. But it is most strongly supported based on the argument that a human is not the source of virus spreading.
I hope this helps. Please let me know if you have any other questions!