Simmons MM; Harris P; Jeffrey M; Meek SC; Blamire IW; Wells GA Central Veterinary Laboratory, New Haw, Addlestone, Surrey. Vet Rec 138: 175-7 (1996)Two annual, random samples of clinically suspect cases of bovine spongiform encephalopathy (BSE) were taken in 1992-93 (year 1, 1500 cases) and 1993-94 (year 2, 1000 cases). From each sample, 100 positive cases were examined in detail to establish the severity of the vacuolation in 17 specific neuroanatomical locations. The resultant 'lesion profiles' were compared with the profile obtained from a similar sample of BSE-affected cattle from early in the epidemic (1987-89); the comparison showed that the distribution and severity of vacuolation in BSE has remained unchanged. The cases not confirmed as BSE on histological examination (172 in year 1 and 162 in year 2) were examined for evidence of any alternative neurohistological diagnosis.
As in previous studies, the majority of these cases showed no significant lesions (61.6 and 61.7 per cent). The remainder consisted of bilateral focal spongiosis of unknown significance (26.7 and 21.0 per cent), inflammatory conditions (8.1 and 11.1 per cent) and a small number of cases with tumours, cerebrocortical necrosis or idiopathic brainstem neuronal chromatolysis. No evidence was found of any cases of BSE with an atypical distribution of lesions. These findings support the theory that the BSE epidemic is sustained by a single, stable strain of the BSE agent, and confirm that the existing statutory diagnostic criteria continue to be appropriate.
'Remember how BSE started out all those years ago? Just a few cattle, no threat to human health, nothing to worry about, etc? Well, I had a distinct feeling of deja vu when I read the first of the two articles attached. This could be nothing at all, or it could be the first inkling of another impending disaster.'
The recent Veternary Record article compared the herds of origin and birth cohorts of the (approx) 58,000 pure breeding cattle exported from the UK in 1985-90, estimating that there should have been 1,670 cases of BSE as compared with the 40 or so declared.
This indicates an awfully large estimated disease rate (10-20%?) in some birth cohorts from these herds. Stuart Neilson did estimate figures in that range for the highest observed susceptibility in British herds.
In the UK we have about 50 animals a week slaughtered as BSE suspects which on post-mortem turn out to have other conditions: hypomagnesaemia, brain tumours, etc., which produce similar symptoms.
Thus since 1990 approximately 15,000 such cases have been reported in the UK, as opposed (for instance) to 151 in France. Has the non-confirmation rate increased in the UK? It used to be (on average) 15 %.
Non-confirmation in Denmark
A very similar number of suspect cases have been histopathologically examined for BSE in Denmark since 1990. All but one were diagnosed as BSE-negative (the single positive was a cow imported from the UK at age 1 year -- originating from the heavily affected 86/87 birth cohort)
Histopathological examination of suspected BSE in Denmark