the invention concerns the use of fosfonowych lysine and arginine analogues of the general formula i, in which r is substituent (4 - amino) butanoic acid, (3 - guanidyno) propanoic acid, (4 - amino) benzyl (4 - guanidyno) benzyl (4 - guanidyno) phenyl, (4 - amido) phenyl as protease inhibitors ekspresjonowanej p for west nile virus (wnv).