Every disease is explained in the manual that the mod adds!
Here it is:
Gives a strange FOV effect to the playerand slows him down.
Slows the player and with Hydrophobia you wil get damage by swimming In water.
Slows the player and has a 50% chance of killing him.
As for the bubonic plague a new mob was added (not really just silverfish retextured) :
The Black Rat
Influenza and Rabies have got a cure:
The Cure is crafted with 1 bucket 2 sugar and 1 redstone!
The Cure will have 4 uses.
Tap on the ground to use one.
First of all, to use any mod/mods you will need Blocklauncher
or Blocklauncher pro. You can find it on the app store (for kindle and android only).
Step 1 : Download any mod/mods of your choice.
Step 2 : Open Blocklauncher(free/pro).
Step 3 : Click the wrench icon near the top of your screen.
Step 4 : Click the manage ModPE scripts option.
Step 5 : Click the import button.
Step 6 : Click the Local storage button.
Step 7 : Find where the mods that you downloaded went (usually under downloads).
Step 8 : Click the mod that you wish to install.
Step 9 : Enjoy the mod/mods that you installed.