Nature 461, 529–532 (2009)

In this Letter, there was an error in the calculation of infectious doses. The correct sentence should read: Assuming a constant infectious dose of 0 log ID50 units in 3 mg of faeces (equivalent to 2.5 log ID50 units per gram of wet faeces), the cumulative total dose of prions shed during a 10-month period based on 780 g wet weight of faeces produced per day1 is 7.9 log ID50 units, which is similar to 7.8–9.3 log ID50 units found in brains of terminally sick mule deer, assuming an average brain weight of 200 g. Because the estimated values in faeces and deer brain are both ∼1,000-fold lower than originally published, this error does not affect the overall conclusions of the paper.

It is noteworthy that mule deer brain samples were bioassayed in Tg(ElkPrP) mice by inoculation of 30 µl of a 1% (w/v) homogenate, and faecal samples by inoculation of 30 µl of a 14% (w/v) homogenate. The resulting ID50 units in brain and faecal homogenates were normalized to reflect the ID50 units in 30 µl of 10% brain and 10% faecal homogenates to facilitate comparisons (see Supplementary Information associated with original manuscript).