The Salmonella cholerasuis vaccine used in swine is best described as which of the following?

• A. It is a killed vaccine.
• B. It is an inactivated vaccine.
• C. It is a live attenuated vaccine.
• D. It is an avirulent live vaccine.

Answer: (D)

The main idea is that this vaccine uses a live organism that is avirulent in swine. Because the strain can still replicate, it mimics natural infection enough to train the immune system, but it does not cause disease. This combination gives a strong, long-lasting immune response, including mucosal and cellular immunity important for intracellular Salmonella. It’s not a killed or inactivated product, which cannot replicate and typically provides a weaker or differently focused immune response. While a live attenuated description is close, labeling it avirulent emphasizes that the strain is non-disease-causing in pigs, making avirulent live vaccine the most precise description.