Evidence of scrapie transmission via milk

Abstract

BackgroundThe risk of scrapie infection increases with increased duration and proximity of contact between sheep at lambing. Scrapie infectivity has not been detected in milk but cellular prion protein, the precursor of disease-associated prion protein PrPd, has been found in milk from ruminants. To determine whether milk is able to transmit scrapie, 18 lambs with a prion protein genotype associated with high susceptibility to scrapie (VRQ/VRQ) were fed milk from twelve scrapie-affected ewes of the same genotype, and 15 VRQ/VRQ sheep reared on scrapie-free dams served as controls.ResultsThree lambs fed milk from scrapie-affected ewes were culled due to intercurrent diseases at 43, 44 and 105 days of age respectively, and PrPd was detected in the distal ileum of the first two lambs, whilst PrPd was not found in lymphoreticular tissues in the third lamb. A control lamb, housed in a separate pen and culled at 38 days of age, was also negative for PrPd in a range of tissues. Samples of recto-anal mucosa associated lymphoid tissue collected from the remaining 15 live lambs at seven months of age (between five to seven months after mixing) were positive for PrPd in the scrapie milk recipients, whereas PrPd was not detected in the remaining 14 controls at that time. A subsequent sample collected from control lambs revealed PrPd accumulation in two of five lambs eight months after mixing with scrapie milk recipients suggestive of an early stage of infection via lateral transmission. By contrast, the control sheep housed in the same building but not mixed with the scrapie milk recipients were still negative for PrPd.ConclusionThe presence of PrPd in distal ileum and rectal mucosa indicates transmission of scrapie from ewe to lamb via milk (or colostrum) although it is not yet clear if such cases would go on to develop clinical disease. The high level of infection in scrapie-milk recipients revealed by rectal mucosal testing at approximately seven months of age may be enhanced or supplemented by intra-recipient infection as these lambs were mixed together after feeding with milk from scrapie-affected ewes and we also observed lateral transmission from these animals to lambs weaned from scrapie-free ewes.

Expression patterns of Doppel in differential ovine PRNP genotypes: quantification using real-time RT-PCR

“…Lezmi et al (2006) analyzed the accumulation of disease-associated prion protein [PrP(d)] using biochemical and immunohistochemical methods, and the two ARQ/ARQ sheep that had scrapie-like clinical symptoms showed PrP(d) in the central, sympathetic and enteric nervous systems and in lymphoid organs. In VRQ/VRQ lambs fed with VRQ/VRQ scrapie sheep milk, Doppel was detected in the distal ileum 43 days later and in the lymphatic system 44 days later (Konold et al, 2008). The present findings were similar to previously reported data, where PRND mRNA was higher in ARR/ARQ than ARH/ARQ in brain, colon, ileum, cecum, and uterus, and where PRND mRNA was higher in ARH/ARQ than ARR/ARQ in thalamus and rectum.…”

Examination of the Offspring of a Japanese Cow Affected with L-Type Bovine Spongiform Encephalopathy

“…Scrapie transmission from ewe to lamb probably occurs via the postnatal route. Detection of scrapie infectivity in the placenta [1] and milk [10] has supported this hypothesis. Further, PrP Sc distribution in cattle experimentally affected with L-BSE was limited to the central nervous system, and little PrP Sc accumulation was observed in the peripheral nerve tissue and adrenal gland at the clinical stage [9].…”

High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect ofPRNPgenotype and age

“…Following earlier epidemiological observations reporting a higher risk of scrapie amongst lambs sucking from infected dams than in those reared artificially [7], evidence of scrapie infectivity in sheep milk [24] and of transmission via sheep milk and/or colostrum has been documented [23]. Sharing of milk/colostrum and cross-fostering of animals were frequent practices within this commercial dairy herd and may have contributed to the rapid increase of disease after the diagnosis of the index case in 2005.…”