What has surprised DEFRA and DEFRA's advising epidemiologists is the speed at which this outbreak has progressed. This has led to a revision of opinion as to the most probable source of the Allendale cases.

In twelve days, from the first case being confirmed on the 23rd of August to the 17th case yesterday, the virus has spread around this area with ferocious speed. This apparent very fast spread may, however, be misleading. It seems very probable that whatever the source, the virus responsible for this local cluster of cases had been present in the area for some time before it was noticed.

Coupled with this is the very fast development of the disease in cattle, which have been going from being free of symptoms to having full-blown disease in a matter of a few hours.

Originally, the Allendale cases were only in cattle and it was assumed that the virus, rather than having persisted in the area since cases here last spring, had crossed over the Pennines from the cases which continue to appear sporadically around Penrith (two yesterday, 2/9/01).

However, when infected appeared amongst these cases, another suggestion is being entertained - namely, that the virus has remained here, perhaps in sheep on Hexham Common, in a latent form. It has then 'mutated' into a very virulent new 'sub-strain' which has shown itself in this new outbreak. This remains a conjecture, but this virus does have the property that it mutates very fast indeed.

The suggestion that Hexham market, which had been used as a mustering point for uninfected animals in the area going for slaughter, was perhaps the source of this new outbreak is now thought unlikely.

Twice the original high security "Blue Box" zone has been extended - when the virus crossed the Tyne, and again yesterday when the seventeenth case appeared above the Derwent Reservoir on the Durham border. This case is inside the Blue Box, but right on its edge, prompting the second extension.

Yesterday the official announcement was made that the carcasses, now 47,000, will go to Tow Law near Durham.

These cases are a bitter blow to a close knit farming community, hit once already last April, in an area where hill farming is marginal. The close co-operation between farms in and around Allendale may have contributed to the speed of spread of the virus over the past two weeks.