a murrain on you

from The Collaborative International Dictionary of English v.0.48

Murrain \Mur"rain\, n. [OE. moreine, OF. morine, fr. OF. morir,
   murir, 8die, L. mori, moriri.] (Far.)
   An infectious and fatal disease among cattle. --Bacon.
   [1913 Webster]

   {A murrain on you}, may you be afflicted with a pestilent
      disease. --Shak.
      [1913 Webster]