Kiran bir sethi uses words that are often associated with disease, like contagious and infection, to explain education and learning. why do you think she makes these associations?

Education and learning do have to do with contagiousness and infection. When a teacher teaches something, it is kind of like a contagious disease. You pass that information on to others very quickly. It "infects" your brain in such a way that retains that info so that it can be used in the long run.