UK dietary exposure to BSE in head meat: by birth cohort and gender.

Background: UK dietary exposure in 1980-1996 to the bovine spongiform encephalopathy (BSE) infectious agent through the consumption of beef mechanically recovered meat (MRM) contained in burgers, sausages and other meat products has already been quantified by birth cohort (born pre-1940, 1940-1969 or post-1969) and gender. In this paper, similar quantification is undertaken for the consumption of bovine head meat.

Methods: Synthesis of evidence on clinical BSE bovines, on bovines slaughtered in the last year of their BSE incubation period, brain contamination during head meat production, brain infectivity (option 1: 1-year preclinical bovine 54% as infectious as clinical BSE bovine; option 2: 1-year pre-clinical bovine as infectious as clinical BSE bovine) and 1980-1996 UK dietary consumption of head meat in burgers, sausages and other meat products.

Findings: Median infectivity consumed in head meat was 49 900 (67 800 for infectivity option 2), 96 200 (126 900) and 24950 (32 800) bovine oral (Bo) ID 50 units for the post-1969, 1940-1969 and pre-1940 birth cohorts in 1980-1989; and 143 950 (266 550 for infectivity option 2), 150 900 (279 500) and 38 350 (71 250) Bo ID50 units in 1990-1996. Males consumed almost 58% of infectivity in 1980-1996. For all three birth cohorts, exposure to BSE in head meat was higher in 1990-96 for both infectivity options. Median infectivity consumed in head meat and beef MRM was 83 150 (109 000 for infectivity option 2), 161 900 (207 450) and 39 300 (50 450) Bo ID50 units for the post-1969, 1940-1969 and pre-1940 birth cohorts in 1980-1989; and 188 200 (348 700), 190 600 (353 050) and 47 200 (87 550) Bo ID50 units in 1990-1996.

Interpretation: Males consumed almost 58% of BSE infectivity in head meat and beef MRM, which is consistent with 60 males of 113 variant Creutzfeldt-Jakeb disease (vCJD) onsets to 30 November 2001. If vCJD onsets to that date had all been infected in 1980-1989, 65 of 113 vCJD onsets in the post-1969 cohort are not consistent with its BSE exposure in 1980-1989 unless the vCJD incubation period or susceptibility depends on age, or another exposure is involved. Experimental data are needed to identify which brain material contaminates head meat, and further pathogenesis data are needed to determine the corresponding infectivity. Other salient sensitivity issues are highlighted.