Table 3

Comparison of infectivity reduction evaluated by bioassay and PMCA assay

SampleAttack rate (%) (no. of clinical animals/no. animals infected)Incubation time (days) (SD)Infectivity reduction (log10)
BioassayPMCA (11)
Scrapie 263K IBH, dilution
    10−1100 (8/8)63 (4)
    10−2100 (9/9)77 (6)
    10−3100 (10/10)85 (6)
    10−4100 (10/10)86 (5)
    10−5100 (10/10)96 (2)
    10−6100 (10/10)103 (2)
    10−7100 (9/9)118 (11)
    10−822 (2/9)219 (243, 194a)
    10−90 (0/10)>300
Bioassay negative control (10% NBH)0/2b>300
Bioassay positive control (10% IBH)5/568 (0)
Positive control 0.01% IBH (ozone quenched with sodium thiosulfate)6/689 (4)
Ozone (13.7 mg/liter) treated for 5 s at pH 4.4 and 4°C0/4b>300>4.12.8
Ozone (13.7 mg/liter) treated for 5 min at pH 4.4 and 4°C0/2b>300>4.1>4
Ozone (12.5 mg/liter) treated for 5 s at pH 6.0 and 4°C5/5124 (30)3.11.9
Ozone (12.5 mg/liter) treated for 5 min at pH 6.0 and 4°C5/6145 (24)3.53.6
Ozone (14.1 mg/liter) treated for 5 s at pH 8.0 and 4°C6/697 (4)1.01.1
Ozone (14.1 mg/liter) treated for 5 min at pH 8.0 and 4°C6/6123 (5)3.12.9
  • a Incubation times for two animals.

  • b Groups each contained animals that were euthanized prior to 300 days (range, 202 to 238 days) due to illness unrelated to scrapie or that tested negative for scrapie and were not included in the calculations. The remaining hamsters had no indication of scrapie at >300 days and were PrPSc negative, as verified by immunohistochemistry after euthanasia.