BSE: Science & research - Transmission of BSE to other species
Concerns that the BSE epidemic could spread to humans and other species of animals resulted in significant research into the transmission of BSE. Early research explored susceptibility to BSE in numerous species and therefore which might have been at risk from BSE infection from, for example, contaminated feed.
TSE diseases can be transmitted between some species under experimental and limited natural conditions. Experimentally, doses of BSE are usually administered either orally or intracerebrally to test if the animal can be infected. Intracerebral inoculations result in the fastest disease progression, but do not represent a likely infection route. Experts agree that it is usually more difficult to transmit a TSE between two species than it is within a species. This is known as the ‘species barrier’ effect. Confirming that BSE could be transmitted to mice was specifically important as this provided laboratory bioassay experiments to discriminate between BSE and other TSEs.
Research has been conducted in the following species:
- Human models: Transgenic mice with human genes
- Sheep and goats
- Pigs
- Chickens
- Deer
- Exotic ruminants
- Mink and cats
In addition, research has also been undertaken to investigate the hypothesis that BSE could be transferred between animals via mites.
Human models: Transgenic mice with human genes
In the 1990s, work conducted in wild type mice and primates indicated that BSE, feline SE and vCJD were indistinguishable and were significantly different to scrapie and sporadic CJD.
Defra, along with other governmental bodies such as the Food Standards Agency, is continuing to fund work investigating the transmission of TSEs to humans. In a recent project, transgenic mice which express the human prion protein were inoculated with BSE and scrapie. Results indicated that there was no evidence of clinical disease resulting from BSE or scrapie in any animals (project SE1439). These humanised transgenic mice develop clinical and pathological signs when inoculated with vCJD (work funded by the Department of Health and the Medical Research Council), suggesting that there is a significant species barrier preventing the transmission of BSE to humans.
Sheep and goats
There is currently no evidence of BSE in the UK sheep population. Research has shown that if sheep are fed BSE-infected cattle brain, they develop a clinical disease which is very similar to scrapie. (More information is available on the experimental BSE in sheep page.)
There has been one case of BSE in a French goat born in 2000. This animal was detected in France in 2002 through the EU wide TSE active surveillance programme. In addition, following re-examination of historic samples, BSE is also suspected in a Scottish goat born in 1987, which was initially diagnosed with scrapie in 1990.
Pigs
Pigs were historically exposed to MBM and therefore the possible transmission of BSE to pigs was studied. It was found that pigs are susceptible to BSE infection if injected intracerebrally with BSE brain homogenate but not when given orally. There is no evidence that pigs can contract BSE through feeding. This research was transferred to the Food Standards Agency in 2000.
Chickens
Chickens were historically exposed to MBM and therefore the possible transmission of BSE to chickens was studied. No evidence was found that chickens can become infected with BSE through feeding. This research was transferred to the Food Standards Agency in 2000.
Deer
Concerns have been raised about the possibility of deer species being exposed to BSE through contaminated feed, particularly as it is known that deer are susceptible to a TSE called Chronic Wasting Disease (CWD). In 2007, the UK implemented an EU surveillance programme for TSEs in red deer. The Food Standards Agency is funding research into the susceptibility of red deer to oral infection with BSE.
Exotic ruminants
Kudu, a type of African antelope and other exotic ruminant species such as Oryx, are known to be susceptible to TSEs as there have been cases of these animals developing BSE following feeding with MBM in UK zoos. Research was conducted by Defra to investigate the pathogenesis and diagnostic patterns from experimental inoculation with BSE (e.g. project SE1835). Kudu were found to be particularly sensitive to BSE. TSE cases from captive animals are recorded on the Defra TSE statistics web page.
Mink and cats
Mink can be affected by a TSE known as Transmissible Mink Encephalopathy (TME). Research was conducted by Defra to see if BSE could be transmitted to mink either orally or intracerebrally. No evidence was found of BSE infection and no incidence of BSE in mink has ever been reported in the UK.
Cats have been diagnosed with Feline Spongiform Encephalopathy (FSE) which is thought to be similar to, if not identical with, BSE. Cases of FSE in domestic cats and large cats in zoos are recorded on the Defra TSE Statistics web page.
The hypothesis that BSE can be transmitted between animals via mites
To examine the hypothesis that BSE could be transferred between animals via mites, mites were fed with BSE- and scrapie-infected brain homogenate but no trace of infectivity could be found when the mites were bioassayed in mice. Another study found no correlation between the presence of mites on farms and the incidence of BSE in cattle and scrapie in sheep. In conclusion, results suggested that mites are unlikely to be vectors or reservoirs of disease (projects SE1828, SE1829).
Links to other information
Page published: 18 March, 2008