What is the difference between the scrapie susceptibility test and the scrapie diagnosis?

• A. The susceptibility test is a genotype test to determine the DNA sequence of the 171 and 136 codons of the gene for the prion protein; the diagnosis of scrapie is made using an immunohistochemistry test to visualize the prion proteins in brain or lymphoid tissue
• B. There is no difference; they are the same test
• C. The susceptibility test is a neurologic evaluation based on
• D. The susceptibility test is an immunohistochemistry test on brain or lymphoid tissue; the diagnosis of scrapie is a test for antibody, the presence of antibody is indicative of infected because once an animal is infected it is infected for life

Answer: (A)

The difference being tested is between a genetic susceptibility assessment and a disease-detection test. In scrapie, susceptibility is tied to the prion protein gene (PRNP), so the susceptibility test looks at the DNA sequence at key codons 136 and 171 to identify which variants an animal carries. This tells you how likely the animal is to develop scrapie if exposed, and it’s used to guide breeding for resistance—not to diagnose an infection.

Scrapie diagnosis, by contrast, confirms whether an animal is currently infected. It does this by detecting the abnormal prion protein (PrP^Sc) in tissues such as brain or lymphoid tissue, typically with an immunohistochemistry test. This shows the presence of the disease process, independent of the animal’s genotype.

So, the susceptibility test is genetic and predictive, while the diagnosis is a tissue-based test that confirms actual infection. The other options mischaracterize the tests: neurologic signs aren’t sufficient for diagnosis, and diagnosis is not about antibodies but about detecting PrP^Sc.