Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2007
Publication Date: 10/18/2007
Citation: Spraker, T., Gidleweski, T., Greenlee, J., Keane, D., Hamir, A., Orourke, K. 2007. Detection of PrP**CWD in retinal tissues in white-tailed deer (Odocoileus virginianus) and Rocky Mountain elk (Cervus elaphus nelsoni) with CWD [abstract]. American Association of Veterinary Laboratory Diagnosticians 50th Annual Meeting. p. 47.
Technical Abstract: Introduction. Chronic wasting disease (CWD), a transmissible spongiform encephalopathy, has been reported in captive and free-ranging mule deer (Odocoileus hemionus hemionus), white-tailed deer (Odocoileus virginianus) and Rocky Mountain elk (Cervus elaphus nelsoni). An abnormal isoform of a prion protein (PrP**CWD) that has been associated with CWD has been reported in numerous internal organs other than the brain and lymphoid tissues, including the retina of mule deer. The objective of this project was to investigate the possibility of PrP**CWD in the retina of white-tailed deer and Rocky Mountain elk with CWD. Materials and methods. Eyes from 80 captive white-tailed deer that were killed during a depopulation program were collected and placed in 10% neutral buffered formalin. None of these 80 white-tailed deer showed any clinical signs suggestive of CWD prior to euthanasia (gun shot); however 79% were positive for CWD by using immunohistochemical staining of the brain stem and head lymphoid tissues. Eyes from 7 captive and 2 research elk were collected and placed in Davison’s fixative. Clinical signs typical of CWD were observed in 5 elk (3 with M/M genotype, 1 M/L and 1 L/L). The other 4 were non-clinical (3 with genotype M/M and 1 L/L), but did have a previous positive rectal biopsy. The globe from each animal was trimmed and embedded in a single paraffin block and sectioned at 5 µm. Tissue sections were stained with H&E and immunostained with Anti-Prion 99 and P4 for the detection of PrP**CWD. Results. Prion was only found in the retina, all other regions of the eye (cornea, lens, ciliary body, iris, choroid, sclera) were free of PrP**CWD in the deer. Examination of the eyes from the white-tailed deer revealed 4 to have detectable PrP**CWD within the retina. PrP**CWD was restricted to the inner and outer plexiform layers of these deer. Sections from all 9 elk had PrP**CWD in 8 of the 10 retinal layers and in the optic nerve. All other regions of the eye were free of PrP**CWD. The most prominent features in the elk were heavy PrP**CWD staining in the inner and outer plexiform layers with minimal intracytoplasmic staining in ganglion cells in the M/M and M/L elk. The 2 L/L elk had minimal PrP**CWD staining in the plexiform layers, but relatively heavy staining in the cytoplasm of ganglion cells and an unusual accumulation of PrP**CWD just inside outer limiting membrane layer. An occasional ganglion cell within the ganglion cell layer contained an intracytoplasmic vacuole in the M/M elk. Discussion/Conclusion. Deer and elk do have an abundance of PrP**CWD in retinal tissues and optic nerve (elk). This accumulation of PrP**CWD may affect vision especially in elk. Genotypes did result in different patterns of PrP**CWD accumulation in elk. The LL genotype at codon 132, which has a prolonged incubation period, had much less PrP**CWD in the retina, especially within the inner and outer plexiform layers. In addition, the LL elk seemed to have more intracytoplasmic staining within ganglion cells as compared to the MM and ML elk.