Rickettsialpox is a mild, self-limiting disease caused by the bacterial organism Rickettsia akari. It is transmitted by the bite of an infected mouse mite (Liponyssoides sanguineus). Primarily an urban disease, it was first discovered in New York City in 1946. Since then a small number of cases are reported in NYC each year. In 2007, there were 14 cases reported among New York City residents (rate of 1.7 cases per 1,000,000 persons).
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You can read more about the history and background of Rickettsialpox in this Wikipedia entry or reference additional info on this NIH/MedlinePlus web page on Rickettsial pox.