Deadly Evolution - Virulence of Viruses

A flu suddenly becomes deadly and kills more than 20 million people. Malaria, once easily treated, has become one of the most persistent diseases of our time. Even new viruses such as HIV exhibit variations in the virus's ability to kill. A variety of factors influence the spread and deadliness of disease, but some biologists think a critical influence has been overlooked--evolution. Producers Marjorie Centofanti and Loretta Williams explore the evolution theories that could lead to change in the treatment of infectious disease.