§ The Countess of Marasked Her Majesty's Government:
What condition is understood by the term "BSE negative" in respect of animals reported as suspected of suffering from BSE, under what conditions is the term applied and in the case of cattle which are subsequently found on post-mortem examination not to be so suffering what attempts are made to establish 85WA the nature and cause of the illnesses and what conditions are reported.
Lord LucasWhen an animal is reported as a suspect, a veterinary officer from the State Veterinary Service carries out an investigation. This will involve differential diagnosis on the basis of clinical signs to determine whether or not a number of other conditions which present similar symptoms are present. If the veterinary officer believes that the animal is a BSE suspect then it is slaughtered and the brain sent for histopathological examination. For technical reasons related to the treatment necessary of the brain samples for microscopical diagnosis, this takes several weeks. A negative diagnosis is given where the typical vacuolation expected at specific target sites in confirmed cases is absent. These criteria have been published by Wells, G A H and others inBovine Spongiform Encephalopathy: diagnostic significance of vacuolar changes in selected nuclei of the medulla oblongata; Vet Record (1989) 125, 521–524. It is not generally possible thereafter when a negative result is confirmed, to carry out further investigations into the nature of the disease. There are a number of conditions which show symptoms similar to BSE, including hypo magnesaemia, hypocalcaemia, ketosis, listeriosis and neoplasia of the central nervous system.
§ The Countess of Marasked Her Majesty's Government:
Whether they are satisfied that the so-called prion is the infective agent in BSE and if so, upon what scientific evidence do they rely for their view.
Lord LucasNo. The background to this issue is set out in the report of the Spongiform Encephalopathy Advisory Committee published in September 1994, which is available in the Library of the House.
There are three main hypotheses:
the prion theory, which suggests that the agent is a small proteinaceous infective particle that resists inactivation by procedures modifying nucleic acids and contains a defective form of the normal membrane PrP protein;
the virino hypothesis, that the agent is an informational hybrid—namely, an infectious pathogen containing a small specific core of non-translated nucleic acid associated with one or more cellular proteins provided by the host;
or a third hypothesis that the agent is an unconventional virus which consists of a nucleic acid that codes for a protective protein coat.
Scientific research continues worldwide, including the UK, to distinguish between these hypotheses. However, in relation to policies to eradicate the disease and protect public health, it is not necessary to take a final view on this question but to rely on empirical information about the characteristics of the agent, its distribution in the tissues of infected animals and its resistance to various inactivation procedures.
The SEAC report also looked at a number of other theories such as intestinal fluid dependent organisms, 86WA nucleation and crystallisation, molecular chaperones, single stranded DNA, green cluster nutrients, the use of high nitrogen fertilisers, bacteria, the neuronal cell membrane hypothesis and organophosphorus compounds, but decided that none to these could be considered viable and justifiable to test until they have been published in peer reviewed scientific journals and the work leading to their evolution verified independently.
§ The Countess of Marasked Her Majesty's Government:
Whether they consider that intracerebral challenge of BSE infective material is an adequate or useful indication of potential for transmissibility of this disease to other species.
Lord LucasIntracerebral challenge of BSE infected material is a useful indication of the potential for transmissibility of the disease to the species being challenged. However there are species, such as the pig, which are clearly susceptible to intracerebral challenge with the BSE agent but nevertheless appear so far in experiments to resist challenge through the oral route. It is well known that the oral route is considerably less efficient than the intracerebral route and that in mice approximately 100,000 times more infective material has to be used orally to establish the disease than by intracerebral injection.
§ The Countess of Marasked Her Majesty's Government:
Whether there is any strain of scrapie which occurs in sheep in the UK which shares similar signs with BSE.
Lord LucasNone of the strains of scrapie which have been tested in the special panel of different strains of mice have shown the same characteristic pattern of disease in those mice as the BSE agent.
As I said in answer to the noble Countess's question of 27th June (Official Report Column 75), the fact that scrapie is changed by passage through other species but BSE is invariant suggests that if BSE was derived from a scrapie strain (as we suspect to be the case) it might well react differently from that strain in the mouse panel.