Characterizing subclinical infection and strain evolution in gene-targeted mouse models of CWD (Authors: Kristen Gregg, Maria Arifin, Anja Itum, Raychal Ng, Samia Hannaoui, Sabine Gilch)

Chronic Wasting Disease (CWD) is the most contagious prion disease and has spread across North America and abroad, affecting deer, moose, elk, and reindeer/caribou. The Prnp gene of cervids is highly conserved, but species-specific single nucleotide polymorphisms (SNPs) have been identified that sometimes lead to single amino acid substitutions in PrP. We have found that the S138N substitution in reindeer has been associated with decreased susceptibility to CWD, with extended pathogenesis and subclinical infection using gene-targeted mice as a model. Here, we seek to understand if subclinically infected 138NN animals contribute to CWD transmission and determine if passage through the S138N environment allows for a new strain of CWD to emerge. CWD isolates from orally infected reindeer expressing either WT or 138SN genotypes were inoculated into gene-targeted mice expressing either the WT or 138NN caribou PrP. None of the 138NN animals showed clinical signs but had evidence of subclinical infection in the fist passage. RT-QuIC positive brain and spleen homogenates of subclinical 138NN mice was inoculated into WT and 138NN gene-targeted mice. Samples from this second passage will be biochemically characterized using PK resistance, conformational stability, and seeding activity. None of the 138NN animals of the second passage showed clinical signs of CWD at the experimental endpoint. Notably, spleen homogenates, in particular of 138NN mice inoculated with 138SS reindeer CWD induced a higher clinical attack rate than brain material in mice. Our findings will shed light on the contributions of subclinical infections on CWD transmission and strain evolution.