how many diseases are there in the world
The current ICD-9 coding has 13,000 entries for different disease states common enough to merit their own code (including those that get placed under otherwise unspecified). So as of this moment in time, there are 13,000 different disease states that are significant enough to require separate insurance-level coding. All this will magically change on October 1st, 2015, when all doctors are mandated to switch over to the ICD-10, which contains 68,000 different coding states for diseases.