There are two main differences between infect and infest. First, infection involves germs or viruses, while infestation involves a menacingly large number of pests or parasites (e.g., mosquitos or rats). Second, an infection applies to a body, while an infestation applies to a place. For example, when rats infest a city, they might carry diseases that can infect people.
These words get tricky when used metaphorically, but it’s easy to keep them straight if you remember the literal distinctions. For example, corruption can infect a government if we think of the government as a metaphorical body, and bad thoughts can infest the mind if we think of the mind as a sort of place and the bad thoughts as pests.
It’s amazing how many of the academy’s bad ideas leak out from campus and begin to infect the body politic. [National Review]
The infamous computer virus Stuxnet was able to infect computers that have no external connection. [Wall Street Journal]
Rinderpest can infect cattle, buffalo and yaks, as well as swine, giraffes and kudus. [Los Angeles Times]
As a seasoned professional farmer, he knows the field needs to be reploughed before pests infest the weedy growths left behind. [Telegraph]
Rural NSW is has been infested with the worst mouse plague in 50 years. [The Canberra Times]