title: Field performance of two rapid screening tests in active surveillance of transmissible spongiform encephalopathies in small ruminants.
abstract: Recently, screening tests for monitoring the prevalence of transmissible spongiform encephalopathies specifically in sheep and goats became available. Although most countries require comprehensive test validation prior to approval, little is known about their performance under normal operating conditions. Switzerland was one of the first countries to implement 2 of these tests, an enzyme-linked immunosorbent assay (ELISA) and a Western blot, in a 1-year active surveillance program. Slaughtered animals (n = 32,777) were analyzed in either of the 2 tests with immunohistochemistry for confirmation of initial reactive results, and fallen stock samples (n = 3,193) were subjected to both screening tests and immunohistochemistry in parallel. Initial reactive and false-positive rates were recorded over time. Both tests revealed an excellent diagnostic specificity (>99.5%). However, initial reactive rates were elevated at the beginning of the program but dropped to levels below 1% with routine and enhanced staff training. Only those in the ELISA increased again in the second half of the program and correlated with the degree of tissue autolysis in the fallen stock samples. It is noteworthy that the Western blot missed 1 of the 3 atypical scrapie cases in the fallen stock, indicating potential differences in the diagnostic sensitivities between the 2 screening tests. However, an estimation of the diagnostic sensitivity for both tests on field samples remained difficult due to the low disease prevalence. Taken together, these results highlight the importance of staff training, sample quality, and interlaboratory comparison trials when such screening tests are implemented in the field.
authors.affiliation: Department of Clinical Research and Veterinary Public Health, NeuroCentre, Reference Laboratory for TSE in Animals, Vetsuisse Faculty, University of Berne, Switzerland. torsten.seuberlich@itn.unibe.ch
authors.forename: Torsten
authors.initials: T
authors.lastname: Seuberlich
authors.forename: Marcus G
authors.initials: MG
authors.lastname: Doherr
authors.forename: Catherine
authors.initials: C
authors.lastname: Botteron
authors.forename: Alexandra
authors.initials: A
authors.lastname: Nicolier
authors.forename: Heinzpeter
authors.initials: H
authors.lastname: Schwermer
authors.forename: Hervé
authors.initials: H
authors.lastname: Brünisholz
authors.forename: Dagmar
authors.initials: D
authors.lastname: Heim
authors.forename: Andreas
authors.initials: A
authors.lastname: Zurbriggen
mesh_terms: D000818:Animals; D015511:Goat Diseases / Q000175:diagnosis* / Q000453:epidemiology; D006041:Goats; D011159:Population Surveillance; D017096:Prion Diseases / Q000453:epidemiology / Q000662:veterinary*; D011328:Prions; D012756:Sheep; D012757:Sheep Diseases / Q000175:diagnosis* / Q000453:epidemiology; D013557:Switzerland / Q000453:epidemiology; D013997:Time Factors
chemical_list: D011328:Prions