Honestly....
In India , precaution is the key word as is everywhere else you travel to in the 3rd world sense. Yes , JE is a disease caused by the mosquito, there are plently around period after the monsoon months , Hep A&B and typhoid , are basically either food or water borne , so dont eat out ( Street Cart ) and NEVER drink water out at a restaurant , preferably order some bottled water which is readily available. The same goes for home , most of us buy canned water with a bubble dispenser.Like I said in the start its about the common sense you administer to yourself which will see you through , however having said that , there are no gaurantee's in life , so be prepared to face some fevers , sinus headache ( air pollution ) and the occasional upset tummy , they wont kill you , they will toughen you up though and I am sure that this visit to india will by the end of it leave your immune system much stronger.
Just my 2 paise worth , make what you will out of it.
Cheers
Vimd23