ITEM 6 – BARB CASE CLUSTERS
39. Professor John Wilesmith (Defra) updated the committee on the
BSE cases born after the 1996 reinforced mammalian meat and
bone meal ban in the UK (BARB cases). Around 116 BARB cases
had been identified in Great Britain up to 22 November 2005,
mostly through active surveillance. BARB cases had decreased in
successive birth cohorts, from 44 in the 1996/1997 cohort to none
to date in the 2000/2001 cohort. However, 3 BARB cases had
been identified in the 2001/2002 cohort. Backcalculation of the
prevalence of BARB cases indicated a drop from 130 infected
animals per million (95% confidence interval 90-190) in the
1996/1997 cohort to 30 infected animals per million (95%
confidence interval 10-60) in the 1999/2000 cohort. A shift in the
geographical distribution of BSE cases, from the concentration of
pre-1996 BSE cases in Eastern England to a more uniform
14
© SEAC 2005
distribution of BARB cases, had occurred. However, it appeared
that certain post-1996 cohorts had a higher exposure to BSE in
certain areas for limited periods. Several clusters of BARB cases
within herds had been identified (5 pairs, 2 triplets and 1
quadruplet).
40. A triplet of BARB cases in South West Wales had been
investigated in detail. The triplet comprised 2 cases born in
September and October 2001 and a third in May 2002. The
animals born in 2001 were reared outdoors from the spring of 2002
but the animal born in 2002 had been reared indoors. Further
investigation of feeding practices revealed that a new feed bin for
the adult dairy herd had been installed in September 1998. In July
2002 the feed bin was emptied, but not cleaned, and relocated. All
3 BARB cases received feed from the relocated bin. This finding
suggested the hypothesis that the feed bin installed in September
1998 was filled initially with contaminated feed, that remnants of
this feed fell to the bottom of the bin during its relocation, and thus
young animals in the 2001/2002 birth cohort were exposed to
feedstuffs produced in 1998. No adult cattle had been infected
because of the reduced susceptibility to BSE with increasing age.
41. Further investigation of multiple case herds had found no
association of BARB clusters with the closure of feed mills.
42. Professor Wilesmith concluded that there is evidence of a decline
in risk of infection for successive birth cohorts of cattle. The BARB
epidemic is unlikely to be sustained by animals born after 31 July
2000. Feed bins could represent a continued source of occasional
infection and advice to farmers is being formulated to reduce this
risk. There is no evidence for an indigenous source of infection for
the BARB cases.
43. Members considered it encouraging that no other factor, apart from
feed contamination, had been identified as a possible cause of
BARB cases to date. Members commented that this study
suggests that only a small amount of contaminated feed may be
required for infection and that BSE infectivity can survive in the
environment for several years. Professor Wilesmith agreed and
noted that infection caused by small doses of infectious material
was consistent with other studies, and it would appear there is little
dilution of infectivity, if present, in the rendering system.
Additionally it appeared that the infectious agent had survived for 4
years in the feed bin.
44. The Chair thanked Professor Wilesmith for his presentation.
snip...
http://www.seac.gov.uk/minutes/final90.pdf
TSS
39. Professor John Wilesmith (Defra) updated the committee on the
BSE cases born after the 1996 reinforced mammalian meat and
bone meal ban in the UK (BARB cases). Around 116 BARB cases
had been identified in Great Britain up to 22 November 2005,
mostly through active surveillance. BARB cases had decreased in
successive birth cohorts, from 44 in the 1996/1997 cohort to none
to date in the 2000/2001 cohort. However, 3 BARB cases had
been identified in the 2001/2002 cohort. Backcalculation of the
prevalence of BARB cases indicated a drop from 130 infected
animals per million (95% confidence interval 90-190) in the
1996/1997 cohort to 30 infected animals per million (95%
confidence interval 10-60) in the 1999/2000 cohort. A shift in the
geographical distribution of BSE cases, from the concentration of
pre-1996 BSE cases in Eastern England to a more uniform
14
© SEAC 2005
distribution of BARB cases, had occurred. However, it appeared
that certain post-1996 cohorts had a higher exposure to BSE in
certain areas for limited periods. Several clusters of BARB cases
within herds had been identified (5 pairs, 2 triplets and 1
quadruplet).
40. A triplet of BARB cases in South West Wales had been
investigated in detail. The triplet comprised 2 cases born in
September and October 2001 and a third in May 2002. The
animals born in 2001 were reared outdoors from the spring of 2002
but the animal born in 2002 had been reared indoors. Further
investigation of feeding practices revealed that a new feed bin for
the adult dairy herd had been installed in September 1998. In July
2002 the feed bin was emptied, but not cleaned, and relocated. All
3 BARB cases received feed from the relocated bin. This finding
suggested the hypothesis that the feed bin installed in September
1998 was filled initially with contaminated feed, that remnants of
this feed fell to the bottom of the bin during its relocation, and thus
young animals in the 2001/2002 birth cohort were exposed to
feedstuffs produced in 1998. No adult cattle had been infected
because of the reduced susceptibility to BSE with increasing age.
41. Further investigation of multiple case herds had found no
association of BARB clusters with the closure of feed mills.
42. Professor Wilesmith concluded that there is evidence of a decline
in risk of infection for successive birth cohorts of cattle. The BARB
epidemic is unlikely to be sustained by animals born after 31 July
2000. Feed bins could represent a continued source of occasional
infection and advice to farmers is being formulated to reduce this
risk. There is no evidence for an indigenous source of infection for
the BARB cases.
43. Members considered it encouraging that no other factor, apart from
feed contamination, had been identified as a possible cause of
BARB cases to date. Members commented that this study
suggests that only a small amount of contaminated feed may be
required for infection and that BSE infectivity can survive in the
environment for several years. Professor Wilesmith agreed and
noted that infection caused by small doses of infectious material
was consistent with other studies, and it would appear there is little
dilution of infectivity, if present, in the rendering system.
Additionally it appeared that the infectious agent had survived for 4
years in the feed bin.
44. The Chair thanked Professor Wilesmith for his presentation.
snip...
http://www.seac.gov.uk/minutes/final90.pdf
TSS
