After the
initial discovery and characterization of BSE, there was a rapid increase in
incidence over the next 5 years.
- The spread
of the disease was linked to the ruminant-to-ruminant MBM feeding practice
which was prohibited in 1989.
- After
the ban, there was a 3 year lag period before the incidence of the disease
began to decline.
- The 3
year lag between banning of the feeding of ruminant offal to ruminants and
the decline in the BSE incidence, is related to the incubation period of the
disease, i.e. several years separate the exposure to PrPSc and
the clinical manifestations of BSE.
- Most
of the BSE cases were in the United Kingdom, in particular in Great Britain.
click on the image to see incidence of BSE in other countries
The first case
of what is now known as vCJD was described in 1994. It was not till 1996 that
the link between vCJD and BSE was established. At this time, the incidence of
BSE exposure was already on the decline and eventually the incidence of vCJD
should drop as well. Diagnosed cases of vCJD have continued to rise through
2000 (red line in figure) and at this point the number of confirmed and unconfimed
cases (bars in figure) is similar to the total number of cases confirmed in
2000 and yet only half of the 20001 year has passed. Thus the vCJD epidemic
may still be on the rise.
- The lag between
the discovery of BSE and the first known case of vCJD is related to the incubation
period of the disease in cattle (time till enough cattle had been affected
and became clinically ill then eventually entered the food chain for humans)
and the incubation period of the disease in humans once BSE containing food
was consumed.
- Note the y-axis
scales for this plot and that for BSE above (0-40,000 for BSE and 0-25 for
vCJD).
- Almost 200,000
cattle have been diagnosed with BSE; thankfully less than 100 humans have
contracted vCJD.
- Note the incidence
of vCJD is still below that for sCJD, indicating that a person is more likely
to develop TSE without exposure to a known threat than to contract vCJD.
click on image to see the distribution of vCJD within the UK
click on image for similar map showing cases of sCJD