Prion diseases, a fatal neurodegenerative disorder, have been identified in various mammals, including sheep (scrapie), cervids (chronic wasting disease), and humans (Creutzfeldt-Jakob disease). The key event in these diseases is the conversion of the normal cellular prion protein (PrPC) into an abnormal disease-associated isoform (PrPSc).
In 1985, a new prion disease called classical bovine spongiform encephalopathy (c-BSE) was discovered in cattle in the UK. The disease spread rapidly due to the recycling of infected carcasses into the feed chain as meat and bone meal (MBM). Over two decades, c-BSE spread to over 28 countries, including Europe, the US, Canada, and Japan, through infected live animals, contaminated MBM, and livestock feed.
Experimental exposure to c-BSE showed it could be transmitted to sheep, raising concerns about its potential spread in the sheep population, especially with the emergence of variant CJD in humans due to dietary exposure. Susceptibility to prion diseases in sheep is determined by polymorphisms in the PRNP gene, with specific genotypes highly susceptible to c-BSE infection.
Intracerebral inoculation of ARR/ARR sheep with c-BSE resulted in inefficient disease transmission, while oral inoculation failed to transmit the disease or cause detectable prion infectivity or abnormal PrP in tissues. This led to the belief that the ARR/ARR PrP genotype provides strong resistance to c-BSE infection in sheep.
In this study, ARQ/ARQ and ARR/ARR newborn lambs were orally exposed to c-BSE passaged in ARQ/ARQ sheep to determine disease transmission efficiency. The study found that ARR/ARR sheep were not completely resistant to c-BSE infection, and the ARR allele selection may have a limited effect on reducing the risk of c-BSE propagation in sheep populations.
The study highlights the importance of ongoing TSE surveillance and SRM measures in small ruminants to protect against the risk of exposure to this zoonotic agent. While c-BSE infection in ARR/ARR sheep can pose a public health risk, the probability of successful cross-species transmission may be lower than with ARQ/ARQ sheep cases.
But here's where it gets controversial: the study's findings contrast with previous research, suggesting that the ARR/ARR genotype does not provide substantial resistance against the ovine c-BSE agent. This raises questions about the effectiveness of breeding for resistance policies and the potential impact on the sheep industry. What do you think? Is the ARR/ARR genotype truly resistant to c-BSE, or is there more to uncover?
