Brussels, 28 Jul 2006
The EU's current sheep breeding programme is resistant to Transmissible Spongiform Encephalopathies (TSEs) and should continue in the interest of public safety, according to a published opinion from the European Food Safety Authority (EFSA). The programme has been contested by Member States and in scientific publications due to recent infections in sheep of an atypical TSE strain.
TSEs are a family of diseases occurring in man and animals that are characterised by a degeneration of brain tissue, giving a sponge-like appearance. The family includes diseases such as Creutzfeldt Jakob Disease (CJD) in humans, Bovine Spongiform Encephalopathy (BSE) in cattle and scrapie in sheep and goats.
Scrapie is thought to be transmitted horizontally, from one animal to another or via environmental routes, or vertically, from ewe to lamb. Classical strains of the disease denote those that have been around for centuries, while atypical refer to previously undetected strains of the disease. The disease has never been known to have infected humans. To date, BSE in sheep has been viewed as possible, but has never been detected (although there have been suggestions that BSE can be masked by scrapie). Nevertheless, EU measures against BSE have been applied to all farmed ruminants to ensure the highest possible level of public health protection.
Research has shown that sheep with certain genotypes (ARR alleles) are more resistant to scrapie. In 2005, the EU introduced a breeding programme aimed at increasing the level of the ARR allele within the sheep population, while decreasing the level of those genes contributing to susceptibility to the disease. However, since then, cases of the atypical strains of scrapie have been reported in sheep thought to be 'resistant', and experimental studies have transmitted BSE to sheep. This led some Member States to call into question the safety of the breeding programme.
In its opinion, EFSA's panel of biological hazards (BIOHAZ) says that no evidence was found that the programme had any adverse effects. On the contrary, it found that the programme 'increases the robustness of sheep populations against the currently known TSEs and therefore contributes to both improved animal health and consumer protection'. For atypical scrapie, 'the current breeding programme is likely to reduce the animal health problem and human exposure; however, the timescale for the reduction of risk may be longer than for other TSEs.' Nonetheless, the panel recommended more research on atypical scrapie in order to assess any potential human or animal health risks, while noting that this disease is not presently considered as transmissible to humans.
On BSE, the panel considered it unlikely that sheep bred for TSE resistance could infect other sheep with BSE through the placenta and body fluids. In order to keep track of the issue, however, the panel recommended that a Quantitative Risk Assessment of BSE risk in the EU sheep population be carried out on a regular basis, and noted that the BIOHAZ panel would provide such an assessment over the coming months.
Finally, the panel noted that not all sheep would have to be bred carry the resistant genes in order for the programme to be effective. It also advised preserving samples of semen and embryos from sheep carrying the gene types which have been out-bred in order to protect sheep should any unknown adverse effects or new diseases be detected in the future.