Federal regulators moved today to block new home-health agencies from starting up in the Dallas and Houston areas. The reason, in a word: fraud.Specifically, the regulators said they wouldn’t let any new agencies bill Medicare, the federal health insurance program for seniors. The moratorium starts tomorrow and is expected to last at least six months.The move comes nearly two years after federal prosecutors in Dallas said they had busted the largest home-health fraud ever orchestrated by a single doctor. That physician, Rockwall resident Jacques Roy, has since lost his license. He is still awaiting trial.