any swelling of the joints??? Also, where are you (with as much, or as little, specificity as you wish to offer)? If you answer India, or "the Valley", CA then Newcastle is, unfortunately, much more likely - though it was believed eliminated in CA as of early this year.
In Europe, Avian Influenza is (or was, recently) pretty widespread.
What % of your flock, do you estimate, is infected? How big is your flock (so we can guess at mortality rates)? Are they cage kept? tractored? free range? How close are the neighbors? Do they have birds, and are they showing any symptoms? Do you have other avians (ducks, geese, turkey, quail), and do they appear infected?
Not to be morbid, but those things can help with disease differential diagnosis.