Sheep with scrapie and mastitis transmit infectious prions through the milk.

Prions are misfolded proteins that are infectious and naturally transmitted, causing a fatal neurological disease in humans and animals. Prion shedding routes have been shown to be modified by inflammation in excretory organs, such as the kidney. Here, we show that sheep with scrapie and lentiviral mastitis secrete prions into the milk and infect nearly 90% of naïve suckling lambs. Thus, lentiviruses may enhance prion transmission, conceivably sustaining prion infections in flocks for generations. This study also indicates a risk of prion spread to sheep and potentially to other animals through dietary exposure to pooled sheep milk or milk products.

Association of N176K and L141F dimorphisms of the PRNP gene with lack of pathological prion protein deposition in placentas of naturally and experimentally scrapie-affected ARQ/ARQ sheep.

The placenta is important in the horizontal transmission of the aetiological agent in scrapie-affected sheep. It has been demonstrated that the placentas of fetuses carrying the dimorphism Q171R of the PRNP gene is resistant to pathological prion protein (PrP(Sc)) accumulation in the placenta. To test whether other PRNP polymorphisms are associated with a lack of placental PrP(Sc) deposition, we carried out a study on 26 naturally and 11 experimentally scrapie-affected ewes with or without clinical signs. PrP(Sc) was detected in the placenta of ARQ/ARQ(wild type) fetuses by Western blot and immunohistochemical analysis, but not in ARQN(176)/ARQK(176) or, as expected, ARQ/ARR samples. Furthermore, three of four AL(141)RQ/AF(141)RQ placentas were also PrP(Sc) negative, suggesting that the dimorphism at codon 141 may also mediate placental deposition of PrP(Sc). This finding demonstrates for the first time that fetal PRNP polymorphisms, other than those at codon 171, are associated with the lack of placental deposition of PrP(Sc).

Intraepithelial and interstitial deposition of pathological prion protein in kidneys of scrapie-affected sheep.

Prions have been documented in extra-neuronal and extra-lymphatic tissues of humans and various ruminants affected by Transmissible Spongiform Encephalopathy (TSE). The presence of prion infectivity detected in cervid and ovine blood tempted us to reason that kidney, the organ filtrating blood derived proteins, may accumulate disease associated PrP(Sc). We collected and screened kidneys of experimentally, naturally scrapie-affected and control sheep for renal deposition of PrP(Sc) from distinct, geographically separated flocks. By performing Western blot, PET blot analysis and immunohistochemistry we found intraepithelial (cortex, medulla and papilla) and occasional interstitial (papilla) deposition of PrP(Sc )in kidneys of scrapie-affected sheep. Interestingly, glomerula lacked detectable signals indicative of PrP(Sc). PrP(Sc) was also detected in kidneys of subclinical sheep, but to significantly lower degree. Depending on the stage of the disease the incidence of PrP(Sc) in kidney varied from approximately 27% (subclinical) to 73.6% (clinical) in naturally scrapie-affected sheep. Kidneys from flocks without scrapie outbreak were devoid of PrP(Sc). Here we demonstrate unexpectedly frequent deposition of high levels of PrP(Sc) in ovine kidneys of various flocks. Renal deposition of PrP(Sc) is likely to be a pre-requisite enabling prionuria, a possible co-factor of horizontal prion-transmission in sheep.