Prenatal transmission of scrapie in sheep and goats: A case study for veterinary public health

Detection of prions in oocytes and ovaries of ewes naturally infected with classical scrapie

Classical scrapie is a prion disease that affects goats and sheep and is transmitted mainly horizontally. However, infection can also occur vertically, from mother to offspring, but the exact mechanism is unclear. The possibilities include transmission during pregnancy, birth, or after birth. Some studies have reported that prions are present in various reproductive tissues and fluids, suggesting that vertical transmission could occur through the germ line. However, the presence of prions in female reproductive tissues and oocytes has not been extensively studied, so their role in vertical transmission is unknown. Oocytes and ovarian tissues from 25 naturally infected ewes (ARQ/ARQ and VRQ/VRQ genotypes) and healthy controls were analysed. The samples were subjected to PMCA for prion detection. Histopathological and immunohistochemical evaluations of ovarian tissues were also performed. We demonstrated that PrPSc can accumulate in the oocytes and ovaries of scrapie-infected ewes, indicating a potential germline route of transmission. Prion accumulation appears to be influenced by the host genotype and prion strain, emphasizing the need for ultrasensitive detection techniques. Further research under controlled conditions is necessary to elucidate the mechanisms and implications for disease control and breeding programs.

Immunohistochemical study of scrapie in naturally affected sheep in the east of Libya

Background

The most common natural prion disease that primarily affects sheep and goats is scrapie. It belongs to a group of disorders known as transmissible spongiform encephalopathies, which impact both humans and animals.

Aim

The research is aimed to examine and confirm the presence of scrapie in Libya using immunohistochemistry (IHC) techniques.

Methods

Brain samples were collected from thirty-three sheep older than two years of age showing clinical signs resembling to scrapie during the period between 2018 and 2023, regardless of race or gender. Three animals, six months old, healthy, and without any symptoms, were used as negative controls. Different parts of the brain, including the obex and cerebellum, were taken from each case. The IHC technique used in this study involved staining with monoclonal antibody L42 and DAB (3,3'-diaminobenzidine) as a chromogenic substrate.

Results

The IHC examination showed the expression of prion proteins in brain tissue in twenty-three samples. The staining intensity was markedly observed in the neuronal cell bodies and around blood vessels.

Conclusion

The findings of this study provide evidence that scrapie exists in Libya.

Detection of CWD prions in naturally infected white-tailed deer fetuses and gestational tissues by PMCA

Chronic wasting disease (CWD) is a prevalent prion disease affecting cervids. CWD is thought to be transmitted through direct animal contact or by indirect exposure to contaminated environmental fomites. Other mechanisms of propagation such as vertical and maternal transmissions have also been suggested using naturally and experimentally infected animals. Here, we describe the detection of CWD prions in naturally-infected, farmed white-tailed deer (WTD) fetal tissues using the Protein Misfolding Cyclic Amplification (PMCA) technique. Prion seeding activity was identified in a variety of gestational and fetal tissues. Future studies should demonstrate if prions present in fetuses are at sufficient quantities to cause CWD after birth. This data confirms previous findings in other animal species and furthers vertical transmission as a relevant mechanism of CWD dissemination.

Emerging diseases in international trade in embryos

A significant change in cattle production and germplasm exchange has occurred over the past 50 years. The growth of artificial reproductive technologies and their broad implementation has become commonplace. The production and subsequent import and export of semen and embryos throughout the world has increased significantly. The embryo transfer industry has reached a new record of growth, with approximately 1.5 million transferrable bovine embryos collected and/or produced in 2018. Over 1 million of these embryos were produced invitro . The increased production of invitro -produced embryos leads to greater opportunities involving international trade. However, further research concerning emerging pathogens is imperative to ensure the efficacy and safety of the embryo transfer industry. Appropriate biosecurity protocols, including reliable testing methodology and effective embryo processing procedures, are key in preventing disease due to emerging and re-emerging pathogens that can be transmitted via embryo transfer.

Spatio-temporal and risk factor analysis of alleles related to Scrapie resistance in sheep in Great Britain before, during and after a national breeding program

Certain genotypes of sheep have been identified to increase their susceptibility (the VRQ allele) or resistance (the ARR allele) to classical scrapie. This study's aim was to assess the spatio-temporal pattern of the ARR and VRQ alleles in Great Britain (GB) and to explore the risk factors associated to their presence. Data was collected from the GB scrapie active surveillance program, the sheep and goat inventory survey (GB census survey) and the agricultural survey for the period 2002-2015. Spatio-temporal trends of genotypes were assessed through the use of choropleth maps, spatial cluster and linear regression analyses. Multivariable mixed effect logistic regression analyses were performed to investigate the association between the resistant or susceptible genotypes, and breeds, farm purpose, animal purpose, surveillance stream, country location and herd size. The results show a significant upward trend in the frequency of most resistant ARR alleles (1.15% per year, 95%CI: 0.76-1.53) and significant downward trend of most susceptible VRQ alleles (-0.40% per year; 95%CI: -0.69 to -0.10]. The trend continues after the termination of the national scrapie plan in 2009. Breeds such as Herdwick (OR = 0,26; 95%CI: 0.14-0.46), Shetland (OR = 0.22; 95%CI: 0.13-0.39), Swaledale (OR = 0.58; 95%CI: 0.47-0.73), Scottish blackface (OR = 0.54; 95%CI: 0.41-0.71) and Welsh Montain (OR: 0.59; 95%CI: 0.44-0.79) were identified with lower odds ratios of having the resistant ARR allele, while Beulah speckled face (OR = 1.58; 95%CI: 1.04-2.41), Jacob (OR = 2.91; 95%CI: 1.33-6.40), Lleyn (OR = 2.94; 95%CI: 1.28-6.74) and Suffolk (OR = 2.19; 95%CI: 1.69-2.84) had higher odds ratios of having the ARR allele. Other risk factors associated to presence of ARR allele were finishing farms (OR = 1.15; 95%CI: 1.06-1.24) and farms in Scotland (OR = 0,78; 95%CI: 0.73-0.83) and in Lowland grazing areas (OR = 1.53; 95%CI: 1.39-1.67). Factors associated with presence the VRQ genotype were farms in Scotland (OR = 0,85; 95%CI: 0.77-0.93) and breeds such as Herdwick (OR = 2.2; 95%CI: 1.08-4.97), Shetland (OR = 4.12; 95%CI: 2.20-7.73) and Sweledale (OR = 1.51; 95%CI: 1.10-2.09). For the most resistant genotype, two significant spatial clusters were identified: a high-risk cluster in the south-west of GB (RR = 1.51, p < 0.001) and a low-risk cluster in northern GB (RR = 0.65, p < 0.001). For the most susceptible genotypes, one significant high-risk cluster was identified in Wales (RR = 2.89 and p = 0.013). Surveillance for classical scrapie could be improved with a risk-based approach by focussing on those areas and farm types identified to have higher frequency of VRQ alleles and less frequency of ARR alleles. Scrapie control strategies could focus on developing breeding programs on farms with Shetland, Herdwick and Swaledale breeds.