perhaps a bit more debugging?

Failed to call hook 'OnEntityDeath' on plugin 'Diseases v1.0.4' (KeyNotFoundException: The given key was not present in the dictionary.)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x0001e] in <fb001e01371b4adca20013e0ac763896>:0 
  at Oxide.Plugins.Diseases.GetConfigBool (System.String menu, System.String key) [0x00012] in <1ccd47d87d8d4789950165f76ff85f01>:0 
  at Oxide.Plugins.Diseases.OnEntityDeath (BaseCombatEntity entity, HitInfo info) [0x0003f] in <1ccd47d87d8d4789950165f76ff85f01>:0 
  at Oxide.Plugins.Diseases.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x005ec] in <1ccd47d87d8d4789950165f76ff85f01>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <80b90e8213db44b29ec2d4111764172c>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <ec05e0208c9149bba43236ca58fea105>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <ec05e0208c9149bba43236ca58fea105>:0 

oh.. and as a side note.....
perhaps a check if the player is admin ....

After debugging, testing, and rewriting all day, I found that the root issue was adding/removing infected players while the same list is being iterated over in OnTick. There is a now a queue that handles adding/removing players that will only do so after iterating is complete. So this should be fixed in 1.0.5.