In Pasteur's vaccine demonstration, attenuation proved effective against which animal bacterial disease?

• A. Anthrax
• B. Rabies
• C. Cholera
• D. Diphtheria

Answer: (A)

Attenuation weakens a pathogen so it can provoke an immune response without causing the disease. In Pasteur’s famous demonstration, he produced an avirulent form of the anthrax organism, Bacillus anthracis, and used it to vaccinate sheep. When later exposed to the virulent pathogen, the vaccinated animals were protected, showing that the immune system could be trained to defend against a real bacterial infection. This experiment provided strong proof that vaccination with a weakened microbe could prevent disease. The other diseases listed involve different agents or later vaccine approaches, but the historic demonstration focused on protecting against an animal bacterial disease—anthrax.