ABC News has hired a top government doctor as part of an expansion of its medical coverage.

Dr. Richard Besser, who was acting director of the U.S. Centers for Disease Control and Prevention when the swine flu epidemic began, will join the network as senior health and medical editor.

ABC also promoted its longtime health commentator Dr. Timothy Johnson to chief medical editor. Johnson is a regular on “Good Morning America,” “Nightline” and “20/20.”

Besser, a pediatrician, plans to report on obesity, swine flu and other public health issues for multiple programs starting in September.