|"Don't stand so close to me."|
Darnley 'was sick of the petite vérole which we call measles.' Although at Stirling at the time of James' baptism, he wasn't at the ceremony, and kept to his chamber.
The unfortunate Darnley didn't have the option of an MMR vaccine of course, and in any case it is generally thought he was suffering from smallpox, or quite possibly syphilis, rather than measles. Certainly, if it was measles it was the second time he had been claimed to have the disease within two years (which is physically impossible). On both occasions the bout of 'measles' lasted far longer than either it or smallpox should. Likewise syphilis would be entirely consistent with what is know of Darnley's extra-marital activities, and the two outbreaks of rash that can typify the disease's progression in its secondary stage.
A dose of the pox, however, was the least of Darnley's worries, as he was murdered at Kirk o' Fields in Edinburgh on 9 February, but the news had yet to reach France.
All in all, a bad start to the year for him, then.
More on Darnley's conjectured bouts of syphilis can be read here: http://medicalhistory.blogspot.ca/…/how-spirochete-secured-…, and while modern diagnoses of historical diseases is often a highly speculative business, it seems one thing we can be fairly sure of is that Darnley didn't have measles.