§ Mr. PickthallTo ask the Minister of Agriculture, Fisheries and Food if he will make a statement on the progress of the attack rate experiment examining the dose of BSE-infected cattle brain necessary to transmit BSE orally between cattle; and what evidence the experiments have produced on the relationship between the incubation period and the size of the dose. [61558]
§ Mr. RookerIn the so called attack-rate experiment, to determine the minimum amount of BSE-infected cattle brain required to infect cattle by the oral route and the effect dose size may have on the incubation time, groups of 10 cattle were deliberately infected at four months of age by feeding them with either 300, 100, 10 or 1 gram280W of BSE infected brain tissue. The cattle were then observed for the development of disease and killed when judged to be positive by clinical signs. Diagnosis of BSE was confirmed by examination of the brain post-mortem.
The experiment has now been running for 7 years and transmission of BSE has been accomplished with all four different doses of brain. All 10 animals in each group dosed with 300 or 100 grams of brain have been positively diagnosed with incubation periods ranging from 32–42 months and 32–60 months respectively. Seven of the 10 animals in each group dosed with 10 or 1 gram have been positively diagnosed with incubation periods ranging from 44–71 months and 45–71 months respectively. One animal died early from other causes not related to BSE in the group that received 10 grams of brain. All the remaining animals from the groups that received 10 or 1 gram of brain are now showing early clinical signs consistent with BSE.
The results indicate that cattle can be infected by the oral route down to a level of 1 gram of BSE infected cattle brain and that incubation period appears to be prolonged at lower doses.
The experiment has since been extended and groups of cattle have now been challenged with either one, one tenth, one hundredth or one thousandth of a gram of the same infected cattle brain used previously. The experiment has been running for 11 months and all animals are still clinically normal. It is hoped that this phase of the experiment will define the minimum dose of brain required to infect cattle and provide further information relating to the effect on incubation period relative to the infecting dose.