Parinisti measles was a medical condition.

In early 2371, six members of USS Voyager's crew came down with the Parinisti measles. Although it was touch-and-go for a while, The Doctor was able to isolate the endoplasmic virus and replicate it in order to form an antibody. And, although it wasn't altogether clear that he could create an effective vaccine, he worked at it for seventy-four hours straight and was successful in creating an inoculation stopping the virus' spread before it became an epidemic.

He told the story of this achievement to several Vikings later that year, on his first away mission in the holodeck. (VOY: "Heroes and Demons")