Which test best indicates protection against distemper?

• A. Neutralizing antibody
• B. ELISA for IgM
• C. PCR
• D. IDEXX fecal panel

Answer: (A)

Protection against distemper is best indicated by neutralizing antibodies because they directly block the virus from infecting cells, providing a functional measure of immunity. A test that assesses neutralizing activity shows whether circulating antibodies can prevent viral replication, which is the key correlate of protection after vaccination or exposure. Binding antibody tests like ELISA for IgM indicate a recent or active response but do not guarantee the antibodies can neutralize the virus. PCR detects viral genetic material and signals current infection, not protective status, while a fecal panel is not used to assess distemper immunity. So, measuring neutralizing antibody titers best reflects protective immunity.