Suitability of protuberances on the third eyelids of sheep as a biopsy site for lymphoid follicles

Adaptation and evaluation of a rapid test for the diagnosis of sheep scrapie in samples of rectal mucosa

In recent publications, it was shown that disease-associated prion protein (PrP(d)) accumulates in the lymphoid tissue of the rectal mucosa of a high proportion of scrapie-infected sheep at clinical and preclinical stages, regardless of several host factors; PrP(d) can also be detected in biopsy specimens of rectal mucosa, with an increased probability proportional to age or incubation period and with an efficiency almost identical to that of tonsil biopsies. Rectal biopsies have the advantages of providing higher numbers of lymphoid follicles and of being simpler to perform, which makes them suitable for scrapie screening in the field. In biopsy samples, PrP(d) could be demonstrated by immunohistochemical (IHC) and Western immunoblotting methods, and the purpose of the present study was to optimize and evaluate a "rapid test" for the diagnosis of scrapie in rectal biopsy samples. The HerdChek CWD (chronic wasting disease) antigen EIA (enzyme immunoassay) test was chosen and, once optimized, provided specificity and sensitivity figures of 99.2% and 93.5%, respectively, compared with IHC results in the same samples obtained at a postmortem. The sensitivity of the assay increased from 82.1%, when a single rectal mucosa sample was tested to 99.4% for those sheep in which 3 or more samples were analyzed. Similarly, sensitivity values of the HerdChek CWD antigen EIA test on biopsy samples increased from 95% to 100% for sheep subjected to 1 or 2 sequential biopsies 4 months apart, respectively. Thus, a preclinical diagnosis of scrapie in live sheep can be achieved by a combination of a simple sampling procedure, which can be repeated several times with no detrimental effect for the animals, and a rapid and efficient laboratory method.

Clinical and pathological features of experimental scrapie in Irish Blackface Mountain sheep

There have been no reports of natural scrapie in Irish Blackface Mountain (BM) sheep which account for approximately 16% of the Irish national sheep flock. The aim of this study was to determine if Irish BM sheep had unusual clinical and/or pathological features of scrapie which would account for failure to diagnose the disease in this breed. BM (n=7), Texel (n=3) and Suffolk sheep (n=1) of scrapie-susceptible PrP genotypes (ARQ/ARQ and VRQ/ARQ) were orally challenged with scrapie-infected brain inoculum. The incubation period, clinical signs, pathology and distribution of disease specific prion protein (PrP(d)) in scrapie-affected BM sheep were similar to scrapie in the Texel and Suffolk sheep. It was concluded that there was no evidence to suggest that scrapie in BM sheep differs clinicopathologically from scrapie in other breeds of sheep.

Immunohistochemical distinction between preclinical bovine spongiform encephalopathy and scrapie infection in sheep

Sheep are susceptible experimentally to bovine spongiform encephalopathy (BSE), the clinical signs being indistinguishable from those of scrapie. Because of the possibility of natural ovine BSE infection, laboratory tests are needed to distinguish between scrapie and BSE infection. The objectives of this study were to determine whether (1) PrPSc accumulates in biopsy samples of the tonsil or third eyelid, or both, of BSE-infected sheep before the appearance of clinical disease, and (2) such samples from BSE- and scrapie-infected sheep differ in respect of PrPSc accumulations. Homozygous ARQ sheep (n = 10) were dosed orally at 4-5 months of age with a brain homogenate from BSE-infected cattle. Third eyelid and tonsillar biopsy samples were taken at < or = 6 monthly intervals post-infection and examined immunohistochemically for PrPSc. Third eyelid protuberances were difficult to identify, resulting in many unsuitable samples; however, third eyelid samples shown to contain lymphoid follicles were invariably negative for PrPSc. In contrast, tonsillar biopsy samples became positive for PrPSc from 11 to 20 months post-infection. Consistent differences in the morphology of PrPSc granules in tingible body macrophages (TBMs) between BSE- and scrapie-infected sheep were detected with anti-peptide antibodies directed towards amino acids 93-106 of the ovine prion protein: thus, PrPSc appeared as single granules in TBMs of tonsillar sections from BSE-infected sheep, whereas clusters of PrPSc granules were observed within TBMs in the tonsils of scrapie-infected sheep. In contrast, antibodies against epitopes situated N- and C-terminally from the 93-106 region of the ovine prion protein revealed no differences between BSE- and scrapie-infected sheep in terms of PrPSc granules in TBMs.

A paired case–control study of risk factors for scrapie in Irish sheep flocks

We did a case-control study of the association of several animal, flock and management factors with scrapie in Irish sheep flocks. The characteristics of 61 sheep flocks with at least one laboratory-confirmed case of scrapie (1990-1998) were compared to 61 flocks with no history of scrapie and matched by geographical location and attending veterinary surgeon. The 61 scrapie-affected flocks were from the database of known scrapie flocks in the Republic of Ireland at the start of the study. In conditional multiple logistic regression, factors associated with increased odds of scrapie in a sheep flock were (i) larger breeding-flock size, (ii) purchasing replacement sheep through the market, (iii) spreading sheep compost on the land and (iv) disposing of the placenta in the compost. Factors associated with decreased odds of scrapie were (i) using cattle slurry on the land and (ii) feeding proprietary concentrates to lambs.

Scrapie and chronic wasting disease

Scrapie and CWD share many features. There are marked similarities in the clinical presentations, the lesions, and the pathogenesis of these diseases, and some similarities in the epidemiology. Extrapolation from the scrapie model of TSE disease to CWD--which occurs in three different species, and should not be considered to be uniform in their response--may be erroneous, however. Such differences may influence diagnostics (e.g., the amount and distribution of PrPC in these different species), pathogenesis (e.g., the influence of genetics on susceptibility and resistance), and epidemiology (e.g., the mode and dynamics of transmission and influences of domestication). IHC is used widely for diagnostics and in the study of the pathogenesis of scrapie and CWD. This technique holds promise for antemortem diagnosis of infection in the peripheral lymphoid tissues such as lymphoid follicles of the nictitating membrane and the tonsil.

Evaluation of peripheral lymphoreticular biopsy techniques and their clinical side effects in sheep

Tissue samples were collected postmortem from 126 sheep at five lymphoreticular sites by different techniques. The three most successful combinations of sites and techniques were: the third eyelids, using a forceps and scissors, which provided a mean (se) of 5.32 (0.70) lymphoid follicles per 5 microm tissue section, a mandibular lymph node, using a Biopty gun, which gave 1.19 (0.26) lymphoid follicles per 5 microm tissue section, and tonsil, using a biopsy forceps, which gave 1.14 (0.27) lymphoid follicles per 5 microm tissue section. These three techniques were repeated once a month for five months on five sheep under general anaesthesia, and their clinical effects were compared with five control sheep which were restrained and anaesthetised in the same way but from which no biopsies were taken. Most lymphoid follicles (3.47 [0.58] per 5 pm tissue section) were obtained by using the third eyelid biopsy technique. There were no clinical side effects associated with the biopsy procedure. There were increases in the plasma concentration of cortisol in all the animals, suggesting that the restraint and anaesthesia were more stressful than the biopsy procedure.