Diagnosis of preclinical CWD in farmed white-tailed deer in Canada by the immunohistochemical examination of recto-anal mucosa- associated lymphoid tissue (RAMALT)

Authors: BALACHANDRAN, ARU - Canadian Food Inspection Agency; THOMSEN, BRUCE - Animal And Plant Health Inspection Service (APHIS); GIDLEWSKI, THOMAS - Animal And Plant Health Inspection Service (APHIS); SPRAKER, TERRY - Colorado State University; MITCHELL, G - Canadian Food Inspection Agency; SOUTYRINE, ANDREI - Canadian Food Inspection Agency; HARRINGTON, NOEL - Canadian Food Inspection Agency; MUNGER, RANDY - Animal And Plant Health Inspection Service (APHIS); Schneider, David; O'Rourke, Katherine

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/12/2009
Publication Date: 9/22/2009
Citation: Balachandran, A., Thomsen, B.V., Gidlewski, T., Spraker, T.R., Mitchell, G., Soutyrine, A., Harrington, N.P., Munger, R., Schneider, D.A., Orourke, K.I. 2009. Diagnosis of preclinical CWD in farmed white-tailed deer in Canada by the immunohistochemical examination of recto-anal mucosa- associated lymphoid tissue (RAMALT). NeuroPrion Workshop: New developments in TSEs of domestic and wild animals. pg.9

Interpretive Summary: Diagnosis of prion disease [for example, scrapie in sheep and chronic wasting disease (CWD) in elk and deer] relies upon sensitive detection of disease-associated prion protein in the brain or tissues containing lymph follicles. Live animal testing for scrapie disease in sheep has included evaluation of biopsy samples of the tonsil, third eyelid and rectal mucosa. Similarly, diagnosis of CWD in live elk has been recently accomplished through biopsy of the rectal mucosa. This invited report to the annual NeuroPrion meeting summarizes the diagnostic performance (test sensitivity) of various tissue sampling sites that were collected after death. The report summarizes the findings from two different populations of captive white-tailed deer from Saskatchewan, Canada. The diagnostic performance of the rectal mucosa samples were similar but lower than that achieved in two other lymphoid tissues, but greater than that achieved in the brain. While these studies were conducted on tissues collected after death, the findings demonstrate the comparative potential for biopsy of the rectal mucosa in live deer not yet showing signs of disease. While many factors may influence test performance in other deer populations, these studies showed that false-negative diagnosis occurred most often in deer presumed to be in an early stage of disease and carrying a mutation in the prion protein gene (codon 96).

Technical Abstract: This report summarizes the comparative diagnostic performance of postmortem rectoanal mucosa-associated lymphoid tissue (RAMALT) sampling in two white-tailed deer farms from Saskatchewan, Canada. The apparent prevalence of disease in these two farms was 21% and 31%. None of these deer were demonstrating signs consistent with CWD. The overall tissue-specific test sensitivities were ranked: RPLN>tonsil>RAMALT>obex. Test sensitivities in deer having at least one PRNP G96S allele were generally lower but similarly ranked. False negative RAMALT results were associated with early disease progression, as assessed by PrPCWD accumulation scores in the obex, and/or the PRNP G96S allele. The proportion of CWD-positive RAMALT follicles were generally lowest in deer early in disease progression and/or heterozygous at PRNP codon 96. And, as expected, variation in the proportion CWD-positive RAMALT follicles was inversely related to the total number of observable follicles per sample. These comparisons made on samples collected postmortem suggest general diagnostic evaluation of RAMALT samples in white-tailed deer would have intermediate test sensitivity as compared to evaluation of RPLN and obex. While many factors may influence actual test performance, early stage of disease progression and the PRNP G96S allele are two that were associated with lower test sensitivities.