Preclinical diagnosis of chronic wasting disease in captive mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus) using tonsillar biopsy.

The usefulness of tonsillar biopsy on live deer for preclinical diagnosis of the transmissible spongiform encephalopathy chronic wasting disease (CWD) was evaluated. Disease was tracked in a CWD-endemic herd using serial tonsillar biopsies collected at 6 to 9 month intervals from 34 captive mule deer (Odocoileus hemionus) and five white-tailed deer (O. virginianus). Tonsillar biopsies were examined for accumulation of PrP(CWD), the protein marker for infection, using immunohistochemical (IHC) staining. 26/34 (76%) mule deer and 4/5 (80%) white-tailed deer had PrP(CWD) accumulation in tonsillar biopsies; CWD was subsequently confirmed by post-mortem examination in all 30 of these tonsillar-positive deer. Six mule deer with IHC-negative tonsillar biopsies had positive brain and tonsillar IHC staining upon death 12 to 40 months following the last biopsy. PrP(CWD) accumulation in tonsillar biopsy was observed 2 to 20 months before CWD-related death and up to 14 months before onset of clinical signs of CWD. Tonsillar biopsies from 3-month-old mule deer (n=6) were IHC negative, but PrP(CWD) accumulation was detected in tonsillar biopsies from 7/10 mule deer by 19 months of age. Tonsillar biopsy evaluated with IHC staining is a useful technique for the preclinical diagnosis of CWD in live mule deer and white-tailed deer when intensive management approaches are possible.