The fear was infectious – fear is not an object that can physically infect people, therefore this quote is a metaphor. This means that it doesn’t make sense as fear is not infectious, therefore this quote is incorrect but it has a greater meaning which overall makes it acceptable.
The greater meaning of this quote is that something is making joe Simpson scared. This could be from an object such as the crevasse, or a sudden realisation that he is most likely going to die. As joe has seen or realised these things, the fear corrupted him like an infection, but only living things can be infectious. As fear can be infected from something else like in these situations, it is acceptable to describe fear as infectious.
The effect this quote gives is that you feel bad for joe. This is because the fear is described as infectious, so if you were in his position, you would be scared.