What is EEE? The mosquito-borne virus that killed a New Hampshire man, explained.

A New Hampshire man has died of eastern equine encephalitis, also called EEE, prompting questions about the rare mosquito-borne disease.

The 41-year-old was hospitalized due to severe central nervous system disease and died within a week. He was healthy and had no underlying conditions.

Eastern equine encephalitis is "exceedingly rare," Dr. Céline Gounder, CBS News medical contributor and editor-at-large for public health at KFF Health News, said on "CBS Mornings" Wednesday.