In “Evolution of Infectious Disease”, 1996, Dr. Paul Ewald, an evolutionary biologist, proposed the faster pathogens are transmitted from person-to-person, the more virulent and resistant to treatment the pathogens become. In “Plague Time: The New Germ Theory of Disease”, 2000, Dr. Ewald proposed that antibiotic resistance is of greater concern when treating acute disease, because pathogens are transmitted more quickly and easily from person-to-person during acute disease than in chronic disease. He also proposed the same antibiotics should never be fed to animals for the same diseases the antibiotics are used for in humans, or the antibiotics would become ineffective.